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184 Background: SETD2, a key methyltransferase modulating histone 3 gene transcription, has been shown to act as a tumor suppressor gene by reducing oxidative stress, colonic inflammation and tumorigenesis in animal models. SETD2 gene expression has been reported to be significantly downregulated in CRC and linked with poorer patient survival. Additionally, SETD2 plays an important role in DNA repair and loss of function mutations have been associated with increased tumor mutational burden (TMB), mismatch repair (MMR) deficiency, and benefit from immunotherapy. Hence, we aimed to characterize the molecular features associated with SETD2 gene expression in CRC. Methods: 15,425 CRC tumors tested at Caris Life Sciences (Phoenix, AZ) with NextGen Sequencing on DNA (592 genes or whole exome sequencing), RNA (whole transcriptome sequencing), and IHC were analyzed. SETD2-high and -low expression were defined as ≥ top and < bottom quartile of SETD2 transcripts per million (TPM), respectively. Cell infiltration in the tumor microenvironment (TME) was estimated by QuantiSEQ. Mann-Whitney U and X2/Fisher-Exact tests were applied where appropriate, with P-values adjusted for multiple comparisons ( q < .05). Gene expression profiles were analyzed for transcriptional signatures predictive of response to immunotherapy (T cell-inflamed) and MAPK pathway activation (MPAS). Real-world overall survival information was obtained from insurance claims data and Kaplan-Meier estimates were calculated for molecularly defined patients. Results: SETD2 expression was significantly increased in left-sided/rectal compared to right-sided tumors (median TPM [mTPM] 55.8 vs 51.1, q < .001). SETD2 mutations were associated with reduced SETD2 expression in pMMR/MSS CRC (mTPM 37.9 vs 54.3 in WT, q < .001), although not statistically significant in dMMR/MSI-H CRC (mTPM 43.6 vs 51.7 in WT, P = .17). Compared to SETD2-high tumors, SETD2-low was associated with increased rates of TMB-high (10.4% vs 8.2%, P = .009), dMMR/MSI-H (7.3% vs 5.6%, P = .02), and PD-L1 IHC levels (4.4% vs 2.5%, q < .002). Only minor differences in gene mutation and copy number rates were observed between SETD2-high and -low tumors , whereas SETD2-high TME was associated with increased immune cell infiltration, including neutrophils, B cells, NK cells, M2 macrophages, and dendritic cells ( q < .05). SETD2-high was also associated with increased T cell-inflamed and MPAS signatures (152% and 159% median increase, respectively, q < .001), regardless of tumor MMR status. Among dMMR/MSI-H CRC, SETD2-high tumors receiving immune checkpoint inhibitors had longer time-on-treatment (HR: 0.39, 95% CI: 0.2-0.76, P = .005) and a trend towards longer OS (HR: 0.29, 95% CI: 0.07-1.2, P = .069). Conclusions: Our data show distinct immune biomarkers and TME cell infiltration associated with SETD2 gene expression in CRC. These findings support a key role for SETD2 in modulating anti-tumor immunity and TME.

185 Background: Down syndrome (DS), a genetic disorder caused by trisomy of chr 21, is associated with a considerably lower risk for solid tumors and other angiogenesis related diseases. DSCR1 belongs to a family of evolutionary conserved protein-coding genes located on chr 21 and is highly upregulated in DS patients. Its product, calcipressin-1, has been shown to reduce cancer risk by suppressing angiogenesis. We previously reported that a germline polymorphism in DSCR1 was associated with time to recurrence in resected CRC and anti-VEGF treatment outcomes in metastatic CRC. Here, we analyzed the molecular landscape of CRC according to DSCR1 expression levels. Methods: 20,237 samples from CRC tested at Caris Life Sciences (Phoenix, AZ) with WTS (Illumina NovaSeq) and NextGen DNA sequencing (NextSeq, 592 Genes and NovaSEQ, WES) were analyzed. Top quartile transcripts per million (TPM) for DSCR1 expression were considered high (Q4) while bottom quartile low (Q1). Cell infiltration (CI) in the tumor microenvironment (TME) was estimated by RNA deconvolution analysis using QuantiSEQ. Interferon-gamma and T-cell inflamed signatures were also calculated from RNA data. X2 and Fisher-Exact tests were used and statistical significance was determined as P-value adjusted for multiple comparisons ( q < 0.05). Results: DSCR1 expression was higher in primary tumors than metastases (10.5 vs 8.1 median TPM, q < 0.05). No significant difference was observed in right- versus left-sided tumors, however rectal tumors showed the highest DSCR1 expression ( P < 0.05). Overall, high DSCR1 TPM were associated with TMB-high (11.3% vs 9.3%), dMMR/MSI-H (7.9% vs 5.9%), and PD-L1 (4.7% vs 3.1%) ( q < 0.01); the association with TMB-H was not significant in pMMR/MSS. DSCR1 high was associated with lower mutation rates of APC, KRAS, TP53 and amplification of FLT1/ FLT3, while higher mutation rates of KMT2C/D, BRAF, PTEN, RNF43, and RSPO3 fusions ( q < 0.0001). Gene set enrichment analysis showed that high DSCR1 expressing tumors were enriched in alterations of several pathways including hypoxia, apoptosis, DNA repair, KRAS signaling, inflammatory response, and oxidative stress-related pathways (all P < 0.05, FDR < 0.25). B cells, macrophages, neutrophils, NK cells, Tregs, cancer associated fibroblasts and endothelial cells were more abundant in the TME of tumors with high DSCR1 while myeloid dendritic cells were lower, regardless of MMR status (all q < 0.001). DSCR1 expression was associated with a higher T-cell inflamed signature and IFN score ( q < 0.05). Conclusions: This is the first and most extensive profiling study to investigate DSCR1 expression in CRC. Our data show a strong association between tumor DSCR1 gene expression and distinct molecular features and TME cell infiltration. These findings suggest that DSCR1 holds potential as a novel therapeutic target for CRC and may be an important player in TME modulation.

4048 Background: Claudins are transmembrane proteins which maintain the tight junction between cells. The stomach specific isoform, CLDN18 isoform 2 (CLDN18.2), is emerging as a promising treatment target because of high expression in GC cells, including targeting via adoptive T-cell strategies. We characterized the molecular features associated with CLDN18 isoform 1 and 2 ( CLDN18.1/ 18.2) gene expression in GC. Methods: Tumor profiling was performed from 1967 samples by NextGen Sequencing on DNA (592 genes or WES) and RNA (WTS) at Caris Life Sciences (Phoenix, AZ). EBER (Epstein Barr Virus) was tested by CISH. Top quartile transcripts per million for CLDN18.1/18.2 were considered high while bottom quartile low expression. X2, Fisher-exact, and Mann Whitney tests were used and significance adjusted for multiple testing by Benjamini-Hochberg (q .05) and EBER (2.15% vs 6.31%, p .05). There were more prevalent ARHGAP26 fusions in the CLDN18.1/18.2 high group (18.1: 9.5% vs 3.86%, p =.001; 18.2: 10.1% vs 0.9%, q .05) and TMB-H (19.6% vs 12.2%, p .05). Similarly, CLDN18.1/18.2 displayed an inverse relationship with M1 Macrophages, NK cells, CD4+ T cells, myeloid dendritic cells in the TME ( q

3129 Background: Disruption of the circadian clock has been linked to cancer risk, development and progression. Core clock proteins are emerging as novel therapeutic targets in cancer. We previously showed that polymorphisms in clock genes were associated with anti-VEGF treatment outcome in metastatic CRC. Here we further evaluated the molecular landscape of clock pathway alterations in CRC. Methods: 7591 CRC tested at Caris Life Sciences (Phoenix, AZ) with WTS (Illumina NovaSeq) and NextGen DNA sequencing (NextSeq, 592 Genes and NovaSEQ, WES) were analyzed. Clock gene Score (CS) was determined using expression of core clock genes Z scores (positives of CLOCK, ARNTL, RORA/B/C and negatives of repressors CRY1/2, PER1/2/3, REVERBA/B) stratified by quartiles. xCell was used to quantify cell infiltration in the tumor microenvironment (TME). Consensus molecular subtypes (CMS) were assessed by RNAseq. Significance was determined as P-values adjusted for multiple testing ( q) of

3538 Background: PTPRT is a protein coding gene involved in signal transduction and cellular adhesion. It acts as a tumor suppressor gene and mutated PTPRT has been implicated in the early metastasis of CRC. PTPRT mutations have been reported as independent potential biomarkers for bevacizumab resistance in metastatic CRC and linked to improved response and survival of patients treated with checkpoint inhibitors in several tumors. Here we characterized the molecular features and clinical outcomes associated with PTPRT gene expression in CRC. Methods: 15025 CRC tested with NextGen Sequencing on DNA (592 genes or WES) and RNA (WTS) by Caris Life Sciences (Phoenix, AZ) were analyzed. Top quartile transcripts per million for PTPRT expression were considered high (H) and bottom quartile low (L). Cell infiltration in the tumor microenvironment (TME) was estimated by QuantiSEQ. X2, Fisher-Exact, Mann-Whitney tests were used and significance determined as P-value adjusted for multiple comparisons ( Q

3128 Background: Macrophage Erythroblast Attacher (MAEA) plays an important role in actin cytoskeleton rearrangement in macrophages and erythroid cells. We previously reported that MAEA suppresses migration, invasion and enhances chemosensitivity in CRC cell lines. Here we aimed to characterize the molecular features associated with MAEA gene expression in CRC. Methods: 14416 CRC were tested at Caris Life Sciences (Phoenix, AZ) with NextGen Sequencing on DNA (592 genes or WES) and RNA (WTS). Top quartile transcripts per million (TPM) for MAEA expression were considered high (Q4) while bottom quartile low (Q1). Consensus molecular subtypes (CMS) were assessed using RNAseq. Cell infiltration (CI) in the tumor microenvironment (TME) was estimated by QuantiSEQ. X2 and Fisher-Exact tests were used and significance was determined as P-value adjusted for multiple comparisons ( Q < 0.05). Results: MAEA expression was highest in rectal tumors (13.6 median TPM) followed by transverse and right-sided tumors (13.0 and 12.8, respectively) and lowest in left-sided tumors (12.5). Overall, MAEA TPM were associated with higher tumor mutational burden (≥ 10 Mut/Mb) (11.8% vs. 8.2%) and dMMR/MSI-H (8.7% vs. 5.1%) ( Q < 0.0001); however, the association with TMB was not observed in MSS tumors. In the MSS cohort, MAEA expression was the highest in CMS4 (14.9 median TPM) followed by CMS1 (12.5), CMS2 (11.9), and the lowest in CMS3 (10.3, all intergroup Q < 0.05). MAEA high was associated with lower mutation rates of APC and amplification of FLT1/ FLT3 while higher mutation rates of ASXL1, KMT2A/C/D, SMARCA4, FBXW7, PTEN, RNF43, BRCA2, HNF1A in the overall cohort ( Q < 0.05). In the MSS cohort, FBXW7 mutation significance with MAEA high expression held true ( Q < 0.05) while MAEA high expression trended to associate with higher mutation rates of KMT2D, SMARCA4, PTEN, BRCA2 mutations, and a lower frequency of FLT1/ FLT3 CNA ( P < 0.05 but Q > 0.05). High MAEA was associated with higher immune CI in the TME, including B cells, macrophages (M1 and M2), neutrophils, NK cells, Tregs, CD4+ T cells and myeloid dendritic cells both in the overall cohort and in MSS tumors (fold change: 1.11-1.33, all Q < 0.001). Conclusions: Our data show a strong association between MAEA gene expression and distinct molecular features (including CMS and immune biomarkers) and TME cell infiltration in CRC. These findings suggest that targeting MAEA may have relevant clinical applications in selected CRC subgroups and MAEA may be an important player in determining the composition of the TME.

3580 Background: Monoamine oxidases (MAOs), including MAOA and MAOB, are mitochondrial enzymes responsible for catalyzing monoamine oxidation. Increased expression of MAOs were found in several cancer types and high MAOB was associated with worse disease stage and poorer survival in CRC. Positive and negative correlations of MAOB expression with mesenchymal type and epithelial type gene expressions, respectively, have been reported. Hence, we investigated whether MAOB expression is predictive for targeted therapies in mCRC. Methods: 430 mCRC pts treated with either bevacizumab (BEV, n = 224) or cetuximab (CET, n = 206) in combination with first-line chemotherapy within the CALGB/SWOG 80405 trial were included in the analysis. MAOB RNA was isolated from FFPE tumor samples and sequenced on the HiSeq 2500 (Illumina). Overall survival (OS) and progression-free survival (PFS) were compared between groups of pts categorized by tertiles of MAOB expression into high (H), medium (M) and low (L). Hazard ratios (HR) and 95% confidence intervals (CI) were computed from multivariable Cox proportional hazards model, adjusting for age, sex, location, number of metastases, KRAS, MSI status, and treatment with FOLFOX or FOLFIRI. Sensitivity analyses were conducted after stratifying by sex. Logrank P-values describe differences without adjustment for patient characteristics. Results: In CET-treated pts, MAOB-L showed significantly longer OS (median 39.2 vs 30.9 vs 15.9 months, logrank P = 4.7E-05, L vs H (as reference) adjusted HR 0.42, 95% CI [0.27, 0.65]) and PFS (median 13.2 vs 11.8 vs 7.6 months, logrank P = 0.006, L vs H adjusted HR 0.59 [0.40, 0.88]) compared to MAOB-M and MAOB-H, respectively. Similar results were observed when evaluating MAOB expression as a continuous variable. In BEV-treated pts, no significant differences were observed when comparing MAOB expression tertiles; however, pts with lower MAOB expression had significantly better OS, but not PFS, when evaluating MAOB as a continuous variable (Cox LRT P = 0.015, covariate adjusted). In CET-treated pts, the effect of MAOB expression was observed in male but not female pts (OS: median 40.3 vs 30.9 vs 16.1 months by MAOB-L, M, H, respectively, logrank P = 6.8E-05, L vs H adjusted HR 0.33 [0.19, 0.59]; PFS: median 13.8 vs 12.6 vs 7.9 months, logrank P = 0.001, L vs H adjusted HR 0.46 [0.28, 0.79]). A significant interaction was observed between MAOB expression and treatment for OS ( P = 0.010) in males and females combined, but only in males ( P = 0.018) when stratified by sex. Conclusions: Our results suggest that pts with MAOB-L tumors may have greater benefit from CET-based treatment and that targeting MAOB may be a promising strategy to improve patient outcomes. Further validation studies are warranted to develop a novel personalized approach based on MAOB expression in mCRC pts. Clinical trial information: NCT00265850.

3547 Background: TIM-3 is an inhibitory checkpoint glycoprotein found on innate and adaptive immune cells and is highly expressed on tumor infiltrating lymphocytes. TIM-3 and its ligands, Galectin 9 (Gal9), HMGB1 and CEACAM1 play a critical role in immune regulation and preclinical data suggest a role in the pathogenesis of colorectal cancer (CRC). We aimed to characterize the molecular features and prognostic value of TIM3 and its ligands in CRC. Methods: Tumor molecular profiling was performed from 15,026 FFPE samples by NextGen Sequencing on DNA (592 genes or WES) and RNA (WTS) and immunohistochemistry (IHC) at Caris Life Sciences (Phoenix, AZ). Top quartile transcripts per million (TPMs) for TIM-3, Gal9, HMGB1 and CEACAM1 were considered high (Q4) while bottom quartile low (Q1) expression (exp). X2/Fisher-exact tests were used for comparison and significance was determined as P-value adjusted for multiple comparison and this was found for the results reported here ( Q < 0.05). Cell infiltration in the tumor microenvironment (TME) was estimated by quanTIseq. Real-world overall survival (OS) information was obtained from insurance claims data and Kaplan-Meier estimates were calculated for molecularly defined pts. Results: Gal 9/TIM3-high tumors had higher prevalence (prev) of high tumor mutational burden (TMB ≥ 10 Mut/Mb) (12% vs. 8%; 14% vs. 6%), deficiency in mismatch repair (dMMR) (9% vs. 5%; 10% vs. 4%), PD-L1 exp (5% vs. 3%; 7% vs. 2%), and was highest in transverse (Fold Change; FC: 1.05, 1.12) and right sided tumors (1.04, 1.10) compared to left sided tumors, and CMS4. In contrast, HMGB1 and CEACAM1-high tumors had lower prev of dMMR (5% vs. 8%, 3% vs. 12%), PD-L1 exp (3% vs. 5%, 3% vs. 6%) and TMB-H (8% vs. 11%, 6% vs. 16%), and was highest in CMS2. In MSS tumors, Gal9/TIM3-high tumors were associated (assoc) with lower frequency of TP53, amplifications (amp) of FLT1/3, CDX2, FOXO1, and CDK8 while CEACAM1 and HMGB1-high were assoc with higher mutation (mut) rates of TP53, APC, NRAS, amp of FLT1/3, CDX2, CDX8, and lower mut in GNAS, FBXW7 and RNF43. High Gal9 and TIM3 exp was assoc with higher infiltration of B cells, M1 and M2 macrophages, NK cells, CD4+ and C8+ T cells, and Tregs, while high HMGB1 and CEACAM1 exp was negatively assoc with Tregs, M1 macrophages, monocytes and CD8+ T cells. High exp of Gal9, TIM3, HMGB1, and CEACAM1 was assoc with worse OS in the entire cohort (HR 0.90, 95%CI, 0.84-0.97, P = 0.005, HR 0.81, 95% CI, 0.75-0.87, P< 0.00001; HR 0.88, 95% CI, 0.82-0.95, P < 0.001; HR 0.80; 95%CI, 0.74-0.86, P < 0.00003, respectively). Conclusions: Strong assoc were identified between Gal9/TIM3, HMGB1 and CEACAM1 gene exp and IO biomarkers, distinct molecular features, CMS, TME cell infiltration, and patient outcomes in CRC. Significantly different mut frequencies may signify unique subsets of CRC. These findings provide rationale for further evaluation of TIM3 and its ligands in CRC as prognostic biomarkers and potential therapeutic targets modifying the TME.

4046 Background: Tumor specific antigens, such as NY-ESO-1 , are emerging as key tumor immune modulating factors with great potential to be used as therapeutic targets to enhance immunotherapy efficacy and expand treatment options for GC. We sought to compare GC tumors expressing high vs low levels of NY-ESO-1 in terms of immune cell abundance in the tumor microenvironment (TME) as well as distinct molecular features and immune biomarkers. Methods: 1967 tumor samples tested with NextGen Sequencing on DNA (592 genes or WES) and RNA (WTS) by Caris Life Sciences (Phoenix, AZ) were retrospectively reviewed. The top quartile of transcripts per million was considered high while the bottom quartile was considered low NY-ISO-1 expression. Tumor mutational burden (TMB) was calculated based on somatic nonsynonymous mutations. Mismatch repair deficiency/microsatellite instability (dMMR/MSI) status was evaluated by a combination of IHC, fragment analysis and NGS of known MSI loci. Gene fusions were detected based on WTS. X2, Fisher-exact, and Mann Whitney tests were used for comparison and significance adjusted for multiple testing by Benjamini-Hochberg correction ( q < 0.05). Cell infiltration in the TME was estimated by quanTIseq. Gene expression profiles were analyzed for a transcriptional signature predictive of response to immunotherapy (T cell-inflamed signature: TIS). Results: The analysis was focused on primary tumors (N = 1323) in this initial study. Expression of NY-ESO-1 was lower in primary/local than metastases (Fold Change FC met vs primary: 1.60, q < 0.05). NY-ESO-1 expression did not appear to be strongly associated with distinct gene mutation profiles in GC. There were no significant differences between low and high expression of NY-ESO-1 with regards to well established immuno-oncology markers (dMMR/MSI, TMB, PD-L1). However, high NY-ESO-1 expression was positively associated with immune related gene expression including CD274, CD80, CD86, CTLA4, HAVCR2, IDO1, IFNG, LAG3, PDCD1, and PDCD1LG2 (FC low vs high: 0.56 to 0.79, q < 0.0001). High NY-ESO-1 expression was also positively associated with cell abundance in the TME including NK cells (FC = 0.87, q < 0.0001), monocytes (FC = 0.29, q < 0.05), myeloid dendritic cells (FC = 0.66, q < 0.0001), CD4+ non-reg T cells (FC = 0.54, q < 0.0001), and CD8+ T cells (FC = 0.73, q < 0.05). Similarly, tumors with high NY-ESO-1 expression were associated with higher TIS scores ( q < 0.0001). Conclusions: In our large cohort of GC, tumors expressing high NY-ESO-1 displayed a distinct landscape of immune cells in the TME and were associated with high expression of immune related genes, as well as high TIS score, which has been reported to predict benefit from anti-PD-1 treatment. The results of our analysis support an association between a more immunologically active tumor microenvironment and NY-ESO-1 gene expression which may have relevant implications on immunotherapy treatment for GC.

3523 Background: Defensins are antimicrobial peptides that play important roles in innate immune response. Deregulation of beta-defensin-1 ( DEFB1) gene expression has been implicated in several cancers and we previously showed that single nucleotide polymorphisms in DEFB1 are associated with clinical outcomes in patients with metastatic CRC. Hence, we aimed to further characterize the molecular features associated with DEFB1 gene expression in CRC. Methods: 14416 CRC tumors tested at Caris Life Sciences (Phoenix, AZ) with NextGen Sequencing on DNA (592 genes or WES), RNA (WTS) and IHC were analyzed. Top quartile transcripts per million (TPM) for DEFB1 expression were considered high (Q4) while bottom quartile low (Q1). Consensus molecular subtypes (CMS) were assessed using RNAseq. Cell infiltration in the tumor microenvironment (TME) was estimated by QuantiSEQ. X2/Fisher-Exact were used and significance was determined as P-value adjusted for multiple comparison ( Q

177 Background: LRP1B is a member of the low-density lipoprotein receptor family and a tumor suppressor found to be downregulated in colon cancer (CRC). GRM3 is a receptor of glutamate, an amino acid and neurotransmitter. Inhibition of GRM3 reduces CRC cell growth. Recent data from CALGB/SWOG 80405 suggests that mutations (MT) of either LRP1B or GRM3 are associated with better and worse overall survival (OS) in patients treated with bevacizumab (Bev), respectively. We investigate the association of LRP1B or GRM3 mRNA levels with outcomes. Methods: A total of 13,780 CRC tumors (male 7,497, female 6,283) underwent comprehensive molecular profiling (Caris Life Sciences). Analyses included next-generation sequencing of DNA (592 genes, NextSeq, WES, NovaSEQ) and RNA (NovaSeq). Significance with multiple correction was indicated with q, otherwise p value. Gene Set Enrichment Analyses (GSEA) were performed (significance p

246 Background: Neoantigens are short peptides derived from tumor-specific somatic mutations that can bind to HLA molecules and be presented on the cell surface to activate the immune system. Recognition of neoantigens by autologous T cells promotes sensitivity to immune checkpoint blockade of mismatch repair deficient (MMRd)/microsatellite instability high (MSI-H) tumors. Neoantigen-targeted reactivity by autologous T cells has also been reported in microsatellite stable (MSS) tumors. We aimed to comprehensively assess the spectrum of neoantigens in upper GI cancers and identify recurrent immunogenic candidate neoantigens. Methods: 600 tumor specimens including 268 esophageal (EC), 211 gastric (GC), and 121 gastroesophageal junction (GEJ) cancers tested at Caris Life Sciences (Phoenix, AZ) with NextGen Sequencing (NGS) on DNA (whole exome) and RNA (whole transcriptome) were analyzed. MSI status was determined by immunohistochemistry of MMR protein and/or NGS. Immune epitope prediction was performed on translated peptide sequences harboring detected mutations using the NetMHCpan v4.0 method in the Immune Epitope Database, with HLA genotyping performed using arcasHLA. Immune/stromal cell abundance was quantified using the Microenvironment Cell Populations Counter method. Gene expression profiles were analyzed for a transcriptional signature predictive of response to immunotherapy (T cell-inflamed signature, TIS). Results: Overall, the median patient age was 66 years (range 22-90), 72.8% were male, and 33.7% of samples were metastatic site biopsies. MMRd/MSI-H rate was 2.2% in EC, 12.4% in GC, and 2.5% in GEJ. A total of 1172 unique recurrent neoantigens with predicted binding-level affinity for patient specific HLA alleles were identified (317 in EC, 786 in GC, 157 in GEJ), with 442 and 552 neoantigens exclusively associated with MSS and MSI-H tumors, respectively. Across each cancer type, a higher positive TIS score correlated with both immune and stromal cell population abundance in the tumor microenvironment, most notably cytotoxic lymphocyte and monocytic cell types (r > 0.80, P < 0.0001). Recurrent peptides associated with highest average TIS scores resulted from mutation of TP53 (R248W, 2 peptides: 2.8%/3.2% of samples, respectively) and CUX1 (L162F, 1.6%) in MSS EC; REL (D318A, 2.3%) and ERBB2 (V842I, 1.2%) in MSS GC; MSH3 (K383fs, 36%) and ASXL1 (G645fs, 24%) in MMRd/MSI-H GC; and HOXD12 (A70-A71dup , 2.8%) and TP53 (R248Q, 3.7%) in MSS GEJ. Conclusions: This is one of the largest studies to investigate the landscape of recurrent neoantigens in upper GI cancers. We were able to identify candidate recurrent peptides with high HLA binding affinity and an association with a positive TIS signature in both MSI and MSS tumors, supporting the role of recurrent neoantigens as potential cancer immunotherapy targets.

435 Background: Anti-PD-1/PD-L1 combining with antiangiogenic agents has showed encouraging anti-tumor efficacy for treating advanced hepatocellular carcinoma (HCC). Toripalimab, a humanized monoclonal antibody against PD-1, has already been approved for melanoma, nasopharyngeal carcinoma and urothelial carcinoma in China. Therefore, we aimed to assess the safety and efficacy of toripalimab plus bevacizumab as a first-line treatment for unresectable HCC. Methods: This is a multicenter, single-arm, open-label, phase II study. Patients with unresectable locally advanced or metastatic HCC, BCLC stage C or B, Child-Pugh stage A, ECOG PS ≤ 1, at least one measurable lesion, no prior systemic therapy, were enrolled and treated with toripalimab (240mg, IV, D1) plus bevacizumab (15 mg/kg, IV, D1) every 3 weeks as first-line treatment until disease progression, unacceptable toxicity, or consent withdrawal. The primary endpoints were tolerability and objective response rate (ORR, per RECIST 1.1 by investigators). The secondary endpoints included the ORR (per mRECIST by independent review committee), the disease control rate (DCR) and progressive free survival (PFS), DoR, time-to-progression (TTP), time-to-response (TTR) and OS. Tumor response was assessed every 6 weeks. Results: As the data cut-off dateofJune 23, 2021,54 pts were enrolled (males 48; median age 54 years [range 26-68]; ECOG PS 0-1; 87.0% with HBV infection; 74.1% in BCLC stage C; 74.1% had received previous local treatment). All pts received at least one cycle of toripalimab plus bevacizumab treatment with median cycles 10 [range 1-18]. Among 52 evaluable patients, per RECIST v1.1, ORR was 32.7% (17/52) with 1 CR and 16 PR, and DCR was 78.8% (41/52); per mRECIST, ORR was 46.2% (95% CI: 32.2-60.5%) and DCR was 94.2% (95% CI: 84.1-98.8%). The median PFS was 9.9 months (95%CI: 5.5-11.0) and median OS has not reached. Most treatment related adverse events (TRAEs) were grade 1-2. Grade ≥3 TRAEs occurred in 25.9% pts, SAEs occurred in 27.8% pts, and grade ≥3 irAEs occurred in 11.1% pts. No treatment-emergent adverse event (TEAE) leading to death occurred in the study. Conclusions: Toripalimab in combination with bevacizumab as first-line treatment showed promising antitumor activity in patients with advanced HCC, and a manageable safety profile. A randomized phase 3 trial of toripalimab plus bevacizumab versus sorafenib (NCT04723004) are ongoing to further validate the efficacy of combination as first-line treatment in advanced HCC patients. Clinical trial information: NCT04605796.

15 Background: Immune check point inhibitors (ICI) are ineffective in MSSCRC. Combination of ICI with targeted agents has the potential to alter the tumor microenvironment and render these tumors vulnerable to ICI. We report the results of the multicenter study of rego and pembro in a diverse patient population with advanced MSSCRC. Methods: This was an investigator-initiated study and enrolled patients (pts) who had failed/were intolerant of chemotherapy at 3 sites. A 3+3 design was used for phase I to evaluate escalating doses of rego (80,120,160, days 1-14/21) in combination with pembro (200m/q3weeks). The primary endpoint was dose limiting toxicities during the first cycle. For phase II, pts received rego at the recommended phase II dose (RP2D) with pembro. The primary endpoint was progression free survival (PFS). Secondary endpoints were overall survival (OS) and objective response rate (ORR). The study was powered to show an improvement in PFS from 1.9 months (CORRECT data) to 2.85 months. Estimated sample size for phase II was 63 pts. Results: Study started in 7/2019 and accrual completed in 7/2021. Of 73 pts, 10 enrolled in phase I and 63 in phase II. RP2D of rego was 80 mg, days 1-14/21, and 70 pts treated at that dose. As of Sep 14, 11 pts remain on treatment. At baseline, median age was 54 years (23-81), 51% female, 53% white, 19% Asian, 12% black, and 11% Hispanic, median prior lines of therapy 2 (1-5), primary tumor location rectosigmoid/rectal 13%, KRAS mutated 68%, BRAF mutated 5%. Liver metastases was present in 78% of the pts. There was no grade 4 toxicity. The most common grade 3 toxicities were rash (20%), followed by hand-foot syndrome and HTN (7%). Dose modification was required in 14%. The most common reason for discontinuation was disease progression (85%), followed by withdrawal of consent (12%). With a median follow up of 5.3 (range:0.6-24.4) months, median PFS was 2.0 (1.8 -3.5) months, and median OS was 10.9 (5.3-NR) months. In 16 pts (23%), with non-liver metastatic disease PFS was 4.3 (1.9-8.4) months. No objective response was observed. Stable disease was observed in 49% of pts, median duration of stable disease was 2 (0.2-18.8) months. Conclusions: This is the largest trial of combination of ICI + rego in MSSCRC reported to date. The trial didn’t meet its primary endpoint, though the median OS is provocative. Analysis of biomarkers for identification of pts with longer duration of benefit is ongoing. Clinical trial information: NCT03657641.

156 Background: Emerging evidence suggests subsets of the Hippo pathway have multiple functions of tumor development and immune response regulation. Increased understanding of the molecular characteristics of its signaling pathways and the impact on immune cell trafficking will be critical to develop colorectal cancer (CRC) therapies. Methods: A total of 13,008 CRC tumors were analyzed at Caris Life Sciences (Phoenix, AZ) with whole transcriptome and whole exome sequencing (NovaSeq). MSI-H/dMMR was tested by NGS (next generation sequencing), immunohistochemistry (IHC), and fragment analysis. Tumor mutational burden (TMB)-High was determined with a 10-mt/MB cutoff. RNA-deconvolution using QuantiSEQ was used to assess immune cell infiltration in the tumor microenvironment. Consensus molecular subtypes (CMS) were developed using RNA expression data. Gene expression was reported as transcripts per million. Z-score totals of 6 core Hippo genes were calculated in groups: MST1+ STK3 (G1), LATS1+ LATS2 (G2), YAP1+ WWTR1 (G3), and all 6 genes together (G4). Tumors with bottom quartile (QL) z-scores were compared with the top quartile (QH) using χ2/Fisher-Exact test and adjusted with the Benjamini-Hochberg method: adjusted p + T cells were seen in QH than QL with a median fold change of 1.39. G1–4 z-scores all positively correlated with the expression of the analyzed immune-related genes. The highest Spearman rho averages were in HAVCR2 (0.54), CD86 (0.54), CD80 (0.53), PD-L2 (0.5), CD274 (0.46), and LAG3 (0.36). Significantly different mutation rates were seen in QH compared to QL in G1 ( TP53, KRAS, PIKCA, SMAD2, AMER1), G2 ( APC), G3 ( PIK3CA, APC), and G4 ( TP53, PIK3CA, KRAS). Conclusions: The Hippo pathway correlated with immune cell trafficking suggesting that YAP1/TAZ signaling may play a critical role in the immune responses. These findings may help develop novel therapeutic strategies targeting the Hippo pathway combined with immune therapies in CRC.

3537 Background: Aberrant NT signaling has been shown to activate uncontrolled proliferation and dissemination in several gastrointestinal cancer types. Neurotransmitters have been shown to affect endothelial cells and immune cells in the tumor microenvironment to promote tumor progression. We previously showed that single nucleotide polymorphisms in the dopamine and GABA pathways are associated with outcome in patients with metastatic CRC receiving first-line treatment. Here we further evaluated the distribution and molecular context of NT pathway alterations in CRC. Methods: A total of 7,595 CRC tumors tested at Caris Life Sciences (Phoenix, AZ) with NextGen Sequencing on DNA (Next Seq, 592 genes or NovaSeq, WES) and RNA (NovaSeq, WTS) were analyzed. ssGSEA (single-sample gene set enrichment analysis) was used to calculate pathway enrichment scores (ES) of 7 NT gene sets (GABA, nicotinic, muscarinic, dopamine (DA), reelin, glial cell line-derived neurotrophic factor and neurotrophins). X2/Fisher-Exact was used for comparison and significance was determined as p-value adjusted for multiple comparison of ( q) < 0.05. Results: ES based on sample sites showed a substantial heterogeneity in NT enrichment. Notably, when compared to primary tumors, all 7 gene sets were significantly enriched in brain metastases (mets; ES ratio 1.14-1.55), while abdomen, liver, and peritoneal mets displayed significant decreases in most NT gene sets. DA was enriched in ovarian and lung mets (ES ratio: 1.18 and 1.09, respectively), the latter also showing increased neurotrophins ES (1.06) (all q < 0.05). When investigating primary tumors grouped according to overall ES by unsupervised clustering, right-sided and CMS4 CRCs were more prevalent in the high ES cluster compared to the low ES cluster (32 vs 29%, P = 0.02 and 46 vs 30%, P < 0.001, respectively). In addition, tumors in the high ES cluster showed lower prevalence of TMB-H (≥ 10mt/MB) (7 vs 10%), MSI-H (6 vs 10%) and PD-L1 (2 vs 6%), while higher CNA rates were noted in 9 genes (all q < 0.05). High ES tumors showed significant positive associations with microenvironment infiltration of B cells, T cells (NK, CD4+ and CD8+ T cells, but not Treg), M2 Macrophages, Myeloid Dendritic Cell, Neutrophils, and an inverse association with M1 Macrophages, regardless of MSI status ( q < 0.05). Conclusions: This is the first and most extensive molecular profiling study to investigate NT signaling pathway alterations in CRC. Our data show a distinct distribution of pathway enrichment according to metastatic site, distinct molecular features in high vs low ES clusters in primary tumors (including CMS subtypes, TMB, MSI and PD-L1 rates), and differential immune cell infiltration. These findings support the role of NT signaling in the metastatic spread of CRC and modulation of tumor immune microenvironment.

3581 Background: Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase with functions that counter-balance kinase-mediated phosphorylation throughout cell signaling networks. PP2A was reported to upregulate the angiogenesis, while negatively regulate the pathways downstream of receptor tyrosine kinases at multiple nodes. Previous studies showed PP2A variants were associated with the increased risk of cancer. Therefore, we hypothesized that PP2A variants may predict first-line treatment outcome in mCRC pts treated with bevacizumab (bev)/cetuximab (cet)-based chemotherapy. Methods: Genomic DNA from blood samples of pts enrolled in two independent randomized trials, TRIBE (bev arm, n=215, as discovery cohort) and FIRE-3 (bev arm, n=107, as validation cohort; cet arm, n=129, as control cohort), was genotyped through the OncoArray, a customized array manufactured by Illumina including approximately 530K SNP markers. The impact on outcome of 17 selected SNPs in 3 main PP2A core subunits (PPP2CA, PPP2R1B, PPP2R1A), one phosphatase activator (PPP2R4) and 2 endogenous inhibitors (TIPRL, CIP2A) was analyzed. Results: In the discovery cohort, pts with PPP2R4 rs2541164 A/A (N=16) showed significantly shorter overall survival (15.3 vs 27.3 months) compared to carriers of any G allele (N=198) in both univariate (hazard ratio [HR]=1.8; 95% confidence interval [CI]: 1.1-3.1; p=0.02) and multivariate (HR=2.4; 95%CI: 1.4-4.4; p=0.006) analysis. These data were validated in the FIRE-3 bev cohort in both univariate (A/A vs. Any G: 17.3 vs 39.9 months, HR=2.8, 95%CI: 1.4-5.9, p=0.004) and multivariate (HR=4.3, 95%CI: 1.5-12.2, p=0.0095) analysis. Conversely, pts carrying CIP2A rs13069780 C/C (N=24) only showed significantly longer progression-free survival (17.7 vs 12.3 months) than carriers of any T allele (n=105) in the FIRE-3 cet cohort in both univariate (HR=0.6; 95%CI 0.4-0.99; p=0.04) and multivariate (HR=0.5; 95%CI 0.3-0.94; p=0.02) analysis, but no association were observed in the bev cohort of TRIBE and FIRE-3. Conclusions: Our study demonstrated for the first time that PPP2R4 polymorphisms could predict outcomes of bev-based treatment in mCRC patients; Meanwhile CIP2A polymorphism could predict outcomes of cet-based treatment in mCRC patients. These findings support a possible role of the PP2A variants in contributing to resistance to anti-VEGF/EGFR treatment.

3041 Background: CTCs are a promising diagnostic and prognostic biomarker in colorectal cancer. The analysis of CTCs at the single-cell level may allow to capture tumor heterogeneity and identify novel prognostic and predictive markers in mCRC. Our aim was to evaluate whether the transcriptome profile of CTCs was associated with progression-free survival (PFS) in pts receiving treatment for mCRC and whether we could identify significant differences based on pts’ ethnicity. Methods: Single CTCs were prospectively collected from 25 pts undergoing treatment for mCRC at the USC/Norris Comprehensive Cancer Center between April and October 2019. Pre-treatment peripheral blood was processed using CTC-FIND comprised filter separation and immunomagnetic depletion of CD45/50-expressing cells to collect ultra-pure CTCs samples. After isolation to single cell, CTCs were processed by single cell RNA-sequence (scRNAseq). Principal component analysis was used for clustering expression data. DESeq2 was used to identify differentially expressed genes between pts with short ( < 150 days) and long term ( > 150 days) PFS, as well as between Hispanic and non-Hispanic ethnicity with control for FDR ( Q < 0.1). Ingenuity pathway analyses (IPA) of enriched pathway networks were performed. Results: Main pts characteristics were as follow: median age = 52 years; M/F = 18/7; Hispanics/non-Hispanics = 7/18; treatment line (n pts) = 1st (5), 2nd (11), ≥ 3rd (9). We identified 59 single CTC and CTC cluster from 22/25 pts (range 1-9, median = 2/pt). scRNAseq analysis identified two separate clusters of pts based on PFS (short term vs long term). Hispanic pts were mainly distributed within the short term PFS cluster. The IPA of the network of top 40 enriched pathways showed several pathways related with metabolism, such as Sirtuin signaling, mitochondrial dysfunction and oxidative phosphorylation, and IL6/JAK/STAT signaling pathways in pts with short term PFS ( Q < 0.05). When comparing Hispanic vs non-Hispanic pts, we detected enrichment of neuroinflammation signaling pathway in Hispanics, including CXCL8 (fold change, FC: 11.04), GAD2 (FC: 4.77), IRAK3 (FC: 17.06), PLCG2 (FC: 4.65) and TYROBP (FC: 8.43) (all Q < 0.05). Conclusions: In our study CTCs transcriptome profiles showed an association with PFS in pts receiving treatment for mCRC, with an enrichment in mitochondria-related pathways and IL6/JAK/STAT signaling in the CTCs of pts with shorter PFS. Additionally, CTCs scRNAseq identified differentially expressed genes in Hispanic pts, displaying enrichment in neuroinflammation signaling. These results highlight the potential of CTCs molecular profiling as a tool to identify novel prognostic and predictive biomarkers in mCRC and actionable molecular pathways which may impact tumor spread and treatment response

3535 Background: The intracellular DNA sensor stimulator of interferon genes (STING) plays a vital role in anti-tumor immune responses by recognition of self-DNA from tumors and by-products of genomic instability. Activation of STING was reported to enhance cetuximab mediated natural killer cell activation and dendritic cell maturation. Previous reports suggested that polymorphisms of cGAS-STING can affect innate immune response. Therefore, we hypothesized that genetic variants in the cGAS-STING pathway may predict first-line treatment outcome in mCRC pts treated with bevacizumab/cetuximab-based chemotherapy. Methods: Genomic DNA from blood samples of pts enrolled in two independent randomized trials, FIRE-3 (cetuximab arm, n = 129; bevacizumab arm, n = 107) and TRIBE (bevacizumab arm, n = 215), was genotyped through the OncoArray, a customized array manufactured by Illumina including approximately 530K SNP markers. The impact on outcome of 7 selected SNPs in 3 genes involved in the STING pathway (cGAS, STING, IFNB1) was analyzed. Results: In the Cetuximab cohort, pts with STING rs1131769 any T allele (N = 29) showed significantly shorter overall survival (36.3 vs 56.07 months) compared to carriers of C/C (N = 95) in both univariate (hazard ratio [HR] = 2.08; 95% confidence interval [CI]: 1.06-4.07; p = 0.003) and multivariate (HR = 2.98; 95%CI 1.35-6.6; p = 0.00848) analysis; Pts carrying IFNB1 rs1051922 any A allele (N = 68) showed significant shorter progression-free survival (10.23 vs 14.1 months) than carriers of G/G (n = 59) in both univariate (HR = 1.87; 95%CI 1.26-2.78; p = 0.00163) and multivariate (HR = 2.03; 95%CI 1.25-3.3; p = 0.004) analysis. No association were observed in the bevacizumab cohort of TRIBE and FIRE-3. Conclusions: Our study demonstrates for the first time that STING and IFNB1 polymorphisms could predict outcomes of Cetuximab-based treatment in mCRC patients; These finding may provide insight for the combination of STING agonist and anti-EGFR treatment in mCRC patients.

3092 Background: ADP-ribosylation factor 6 ( ARF6) is a small GTPase in the RAS superfamily, which regulates membrane trafficking, remodeling and tumor progression. Preclinical study shows that TP53 and KRAS cooperatively activate the ARF6-AMAP1 pathway which serves as a link by which pancreatic driver mutations promote tumor invasion, PD-L1 dynamics and immune evasion properties in pancreatic ductal adenocarcinoma (PDAC). The clinical impact of ARF6 on cancer progression and prognosis remains unclear. Methods: A total of 2,948 PDAC samples were analyzed using next-generation sequencing of RNA (whole transcriptome, NovaSeq) and DNA (NextSeq, 592 genes or NovaSeq, whole exome sequencing) and immunohistochemistry (IHC) (Caris Life Sciences, Phoenix, AZ). QuantiSeq (Finotello 2019, Genome Medicine) was used to quantify immune cell infiltration. Overall survival (OS) was obtained from insurance claims, and Kaplan-Meier estimates were calculated for molecularly defined cohorts. Significance was determined as p values adjusted for multiple correction ( q) of

3527 Background: Globo H is a carbohydrate antigen that is highly expressed on the cell surface of epithelial cancers but not in normal tissue, and has been reported to correlate with poor prognosis. An attractive therapeutic target, Globo H-targeted agents are being tested in early clinical trials (e.g., OBI-833, a Globo H antigen conjugated to a mutated diphtheria toxin with potential antineoplastic activities, and OBI-999, an antibody-drug conjugate (ADC) consisting of a Globo H monoclonal antibody with a synthetic antineoplastic agent). We aim to describe the molecular features associated with Globo H expression in CRC. Methods: A total of 7,604 CRC tumors were tested by Caris Life Sciences (Phoenix, AZ) by NextGen DNA and RNA sequencing. The expression of β3GalT5, FUT-1 and FUT-2 were evaluated as surrogates for Globo H expression as they are the key enzymes in its biosynthesis. An average z-score of the 3 genes (GloboH) and of β3GalT5 (B3) alone were calculated; tumors with top quartile z-scores were considered expression-high (Q4) and bottom quartile, expression-low (Q1). QuantiSEQ was used to assess immune cell infiltration in the tumor microenvironment (TME). Statistical significance was determined using chi-square/Fisher-Exact and adjusted for multiple comparisons (q=10) (11.4% vs. 8.3%), PD-L1 positive (5.7% vs. 3.4%) and MSI-H/dMMR (8.3% vs. 5.5%). Strong positive associations were seen with mutations in BRAF, KRAS, RSPO3 fusion, and cMYC amplification with B3 alone and GloboH (all q

433 Background: The SLUG gene plays an important role in EMT by repressing E-cadherin and promotes metastasis. Previous data suggest that overexpressed SLUG gene in pancreatic cancer (PC) showing a high frequency of metastasis and poor prognosis. As SLUG contribution to characteristics or metastatic features remains elusive, we clarified its functional roles in PC progression. Methods: A total of 2958 pancreatic tumors were analyzed using Whole Transcriptome sequencing, NextGen Sequencing (NGS) (NextSeq, 592 gene panel) or Whole Exome Sequencing (WES) (NovaSeq) (Caris Life Sciences, Phoenix, AZ). Microsatellite instability (MSI) status was tested by fragment analysis, immunohistochemistry (IHC) and NGS. PD-L1 expression was tested by IHC. Tumor mutational burden (TMB) was measured by counting all mutations found per tumor (a universal cutoff point of ≧10 mutations per MB). Immune cell fraction was calculated by quanTIseq (Finotello 2019, Genome Medicine). Results: A total of 1274 primary and 1684 metastatic pancreatic tumors were included for this study. They were divided equally into four classes in each group, according to their SLUG expression levels. Tumors in the highest quartile of SLUG expression (QH) showed significantly higher frequency in peritoneal-retroperitoneal-omentum metastasis (15.0%) compared to the lowest quartile (QL) (4.8%) (p = .0001). Similar trends were seen in the abdomen (6% vs 1%, p = .001) and bone (2.8% vs 0.0%, p = .005). However, liver (55.0% in QH vs 63.1% in QL) and lung (2.8% vs 14.1%) metastasis occurred most frequently in QL and the least frequently in QH (p = .0197 and p = .001, respectively). This data indicated that tumors with high SLUG gene expression levels tend to lead to disseminated metastasis, and with low expression levels, they tend to spread intravascularly. We detected significant differences among genetic mutations in ATM (5.7% in QL vs 1.8% in QH, p < 0.001) and APC (2.9% vs 0.5%, p < 0.001), and Wnt signaling expressions were higher in QL (4.6%) than QH (0.7%) (p < 0.001). Binary TMB-H and MSI-H tumors had higher frequencies in QL (2.7% and 2.1%) compared to QH (0.3% and 0.1%) (p < 0.001 in both). Contrastingly, PD-L1 expression levels were higher in QH (23.4%) compared to QL (11.0%) (p < 0.001) and had a linear relationship with the expression levels. The median values of the population of B cells, M1 and M2 macrophages were significantly higher in QH compared to QL, but those of myeloid dendritic and CD8+T cells conversely decrease as the SLUG expression increases. Conclusions: Our data indicated the SLUG expression level could determine the tumor characteristics in progression, especially the pattern of metastasis in PC, and it could possibly predict the prognosis and/or therapeutic effects. We also showed immune oncologic markers which have some relationships with SLUG expressions. Further investigation is warranted to better understand SLUG gene functions.

116 Background: Cachexia affects many cancer patients. Growth differentiation factor-15 (GDF15) is a protein that regulates weight and the stress response of cells. The GDF15 gene encodes a ligand of TGF-beta that triggers cachexia and modulates the progression from tumorigenesis to metastasis. Inhibition of GDF15 with an antibody restored muscle mass and fat in animal models. Serum levels rise in proportion to the progression of colon cancer, predict outcome, and have been correlated with CEA. Methods: We retrospectively reviewed 7607 CRC tumors profiled by Caris Life Sciences (Phoenix, AZ) from 2019 to 2020. Profiling included whole transcriptome sequencing (RNA-Seq by NovoSeq). Tumor mutational burden, mismatch repair status, and pathway genomic alterations were evaluated. QuantiSEQ was used to assess immune cell infiltration in the tumor microenvironment. Results: GDF15 expression ranged from 0 to 593 transcripts per million (TPM) with median of 30 (IQR = 15.02). There was no association with age, sex, or primary tumor sidedness. MSI-H/dMMR tumors had higher GDF15 expression (median 37 vs 30, p = 0.0004); TMB > = 17 tumors was seen in 5.9% of bottom quartile (Q1) GDF15 expressors and 8.3% of top quartile (Q4). PDL1 IHC positivity was inversely correlated with GDF15 expression (7.1% in Q1 vs. 2.6% in Q4, p < 0.0001). Genomic alterations associated with higher GDF15 expression (Q4 vs Q1) included genes on TGF-B (SMAD2/4), PI3K (PIK3CA, MTOR), chromatin remodeling (ARID1A, KMT2C), DDR (ATM) and Wnt pathway (APC); those inversely associated included MYC CNA and TP53. Q1 tumors had higher CNA of ERBB2 and FGFR1. Relative neutrophils and NK cells in the TME increased from Q1 to Q4 (p < 0.001). There was a decrease in CD8+ T-cells and Treg cells from Q1 to Q4. Conclusions: GDF15 expression correlates with increased dMMR/MSI-H and TMB, but not with PDL1 expression. Mutations and activated pathways associated with GDF15 expression may explain increased cachexia with more aggressive disease. The association with chromatin remodeling may warrant therapies targeting histone modification and epigenetics. The increase in NK cells but decrease in CD8+ T cells in the TME with increasing GDF15 suggests approaches to treatment. Higher CD8+ lymphocyte counts correlate with PFS with immunotherapy. Anti-PD-L1 therapy reinvigorates the killing function of CD8+ T cells. The decrease in CD8+ T cells and PDL1 positivity with rising GDF15 suggests worse outcome and a lack of response to anti-PDL1 therapy. NK cell checkpoint inhibitors, CARs, and an anti-GFRAL antibody are now in clinical trials and might be utilized in high GDF15 cancers. GDF15 is emerging as a target in the treatment of obesity and cachexia and as a prognostic marker in oncology. Understanding its expression in metastatic colon cancer may reveal which patients could benefit from developing anti-GDF15 targeted therapies against cancer progression.

4598 Background: Isocitrate dehydrogenases (IDH) mutations (mut) identify a distinct subtype of BC that has yet to be fully characterized. We recently showed that IDH1/2 mutant (mIDH) BC harbor specific gene alterations involving chromatin remodeling and DNA repair, and a differential immune markers profile compared to other mIDH GI tumors. Here we aim to further dissect the molecular profile of mIDH BC through a comprehensive gene expression profiling analysis. Methods: 524 BC samples (303 intrahepatic cholangiocarcinoma, IHCC, 67 extrahepatic cholangiocarcinoma, EHCC, 141 gallbladder, 13 unspecified) collected between February to December of 2019 were included. Samples were analyzed using NextGen DNA sequencing (NextSeq, 592 gene panel), whole transcriptome RNA sequencing (NovaSeq) and immunohistochemistry (Caris Life Sciences, Phoenix, AZ). EBseq was used to identify differentially expressed genes in mIDH vs wild type (WT) tumors with control for FDR ( Q < 0.2). Pathway and functional enrichment analysis was performed using g:Profiler and Enrichr. Results: mIDH frequency in our cohort was 11.4% (60/524), with higher prevalence of IDH1 mut (8.8%). IHCC showed the highest mut prevalence: IDH1 13.5%, IDH2 4.6%. mIDH was more common in females ( P = 0.0036). A total of 774 genes were significantly differentially expressed between mIDH and WT: 582 underexpressed (Fold change, FC: 0.025~0.699); 192 overexpressed (FC: 1.43~3.3). Pathway enrichment showed a significant decrease of gene expression in cytokine-cytokine receptor interaction ( Q = 0.002) and inflammatory response genes ( Q = 0.005) in mIDH. Interferon-γ- and PD1 signaling-related genes expression was significantly lower in mIDH vs WT ( Q = 0.02) including IFNG (FC 0.32), NKG7 (FC 0.36), CD8B (FC 0.37), BATF (FC 0.40), PD1 (FC 0.53), SLAMF6 (FC 0.55) and PD-L2 (FC 0.60). Wnt and cadherin signaling were also enriched for altered expression in several genes in mIDH BC ( Q = 3.86e-7 and < 0.00001, respectively). Conclusions: To our knowledge, this is the largest and most extensive gene expression profiling study focused on mIDH BC. Our data show for the first time a distinct gene expression profile characterizing mIDH tumors which display significant downregulation of inflammatory response pathways and immune-related genes. These findings contribute to further the understanding of mIDH BC and may inform the future development of rational combination therapies.

4066 Background: NF1 encodes neurofibromin, which is a key GTPase-activating protein that downregulates RAS activation. Inactivating mutations in NF1 result in sustained activation of RAS signaling, a key driver for development of colorectal cancer (CRC), and have been suggested to be a potential mechanism of resistance to EGFR inhibition in RAS-wild type (WT) CRC. Little is known about molecular characteristics of NF1-mutated (MT) CRC. Methods: Tumor profiles from 8150 CRC patients (pts) with available NF1 mutation status were retrospectively reviewed. NextGen sequencing by a customized 592-gene panel was performed. Microsatellite instability (MSI) / mismatch repair (MMR) status, tumor mutational burden (TMB) and PD-L1 expression were tested. Molecular profiles between NF1-MT and NF1-WT pts were compared. Results: Out of 8150 pts, 176 (2.2%) had somatic NF1 mutations with pathogenic or presumed pathogenic function. A higher NF1-MT frequency was observed in MSI-H/dMMR vs MSS/pMMR (13.5% vs 1.4%, p < 0.0001), in right-sided vs left sided (2.9% vs 1.8%, p < 0.01), and in RAS-WT vs RAS-MT (3.0% vs 1.4%, p < 0.0001). In MSS/pMMR tumors, no association with sidedness was observed (right: 1.3% vs left: 1.2%, NS). The most prevalent co-mutations with NF-1 were APC (63.2%), ARID1A (57.5%), TP53 (51.5%), KMT2D (32.9%) and KRAS (32.4%) in all cases, and APC (76.2%), TP53 (69.5%), KRAS (38.8%), ARID1A (34.4%) and FBXW7 (21.5%) in MSS/pMMR cases. POLE mutation was observed in 18.4% of NF1-MT/MSS/pMMR pts. Compared to NF1-WT pts, NF1-MT pts had more frequent mutations in ARID1A (All: 57.5% vs 23.3%, p < 0.0001; MSS/pMMR: 34.4% vs 15.2%, p < 0.05), and less frequent mutations in KRAS (All: 32.4% vs 49.0%, p < 0.0001; MSS/pMMR: 38.8% vs 50.3%, p < 0.05). Also, NF1-MT pts had more frequent alterations in homologous recombination pathway compared to NF1-WT pts (All: 39.8% vs 7.5%, p < 0.0001; MSS/pMMR: 17.5% vs 4.4%, p < 0.0001). Mean TMB was significantly greater in NF1-MT than NF1-WT (All: 48.9/Mb vs 10.0/Mb, p < 0.0001; MSS/pMMR: 48.3/Mb vs 8.2/Mb, p < 0.0001). Also, PD-L1 positivity was higher in NF1-MT compared to NF1-WT (All: 12.9% vs 3.6%, p < 0.0001; MSS/pMMR: 7.1% vs 2.6%, p < 0.05). Conclusions: While more frequent than in RAS-MT pts, NF1-MT CRC was a small subset in RAS-WT pts. NF1-MT was associated with alterations in chromatin remodeling and DNA damage response pathways, as well as elevated TMB and PD-L1 expression, which may provide alternative therapeutic strategies beyond EGFR inhibition.

4558 Background: The increased PD-L1 expression evaluated by combined positive score (CPS) is associated with improved efficacy of immunotherapy in GE cancers. The impact of tumor molecular alterations on PD-L1 expression is still not well-studied. We aimed to characterize specific molecular features of tumors with different CPS levels in GE cancers. Methods: 2,707 GE tumors [1,662 gastric/GE junction adenocarcinoma (GA), 856 esophageal adenocarcinoma (EA), 75 esophageal squamous (ES) and 114 GE unspecified] collected between 2000.8 and 2019.7 were analyzed using NextGen DNA sequencing (NGS), immunohistochemistry (IHC) and fragment analysis (FA) (Caris Life Sciences, Phoenix, AZ). Tumor mutation burden (TMB) was calculated based on somatic nonsynonymous missense mutations. dMMR/MSI status was evaluated by a combination of IHC, FA and NGS. PD-L1 expression measured by IHC (22c3) was evaluated by CPS scores. Molecular alterations were compared in three groups (CPS ≥ 10, H; CPS = 1~9, M; CPS = 0, L) using Fisher-Exact or Chi-square and adjusted for multiple comparison by Benjamini-Hochberg. Significance was determined by adjusted (adj) p < .05. Results: Overall, CPS-H, M, and L were seen in 18% (n = 494), 28% (n = 765) and 53% (n = 1,448) of GE tumors respectively. CPS-H was the most prevalent in ES (43%) followed by GA (19%) and lowest in EA (14%). Overall, TMB was similar between CPS-L and M, but was significantly increased in H (average TMB = 8.4 vs. 8.6 vs. 11 mt/MB, adj p < .0001); the effect was seen in EA and GA, but not in ES. An overall significant association between MSI/dMMR status and PD-L1 expression levels was seen (2%, 3.2% and 12% in CPS-L, M and H, adj p < .05) in GE tumors; the significance was seen in GA, but not in EA or ES. Amplifications of PD-L1 (H: 1.5%, M: 0.1% and L: 0) and PD-L2 (H: 1.1%, M: 0.1%, L: 0) were the highest in CPS-H, while ASPSCR1 (H: 0, M: 0, L: 1%) and TNFRSF14 (H: 0, M: 0.4, L: 2%) were the lowest (adj p < .01). Genes involved in epigenetic modification (top 5: ARID1A, ASXL1, BCL9, BCOR, CREBBP), MAPK ( KRAS, MAP2K1) and mismatch repair ( MLH1, MSH6) had the highest mutation rates in CPS-H, compared to M and L ( p < .0001). In contrast, CDH1 had higher mutation rates in CPS-L (12%), compared to M and H (5% and 5%) ( p < .0001). Conclusions: This is the largest study to investigate the distinct molecular landscape of pts with different PD-L1 expression levels in GE cancers. Our data may provide novel insights for pt selection (e.g. pts with gene mutations involved in epigenetic modification) and the development of rational combination immunotherapy (e.g. drugs targeting MAPK pathway).

4064 Background: Abnormal DDR is a hallmark of cancer, relating to genome instability, anti-tumor immunity, and sensitivity to chemotherapeutic agents and radiation. We conducted a large-scale investigation to clarify the alteration of DDR pathway in CRC. Methods: Tumor samples from 9321 CRC patients were retrospectively reviewed. Next-Generation Sequencing (NGS) on a custom-designed panel enriching 592 gene targets was performed. Samples with mutations detected in any of 29 DDR-related genes were deemed DDR-mutant (DDR-MT); the rest DDR-wild type (DDR-WT). Microsatellite instability (MSI) status was tested with a combination of immunohistochemistry (IHC), fragment analysis and NGS. Tumor mutational burden (TMB) was calculated based on somatic nonsynonymous missense mutations. PD-L1 was tested by IHC (SP142). Consensus molecular subtype (CMS) was developed using RNA sequencing data. Results: Of 9321 cases, 1290 (13.8%) were DDR-MT. DDR-MT frequency was higher in right vs. left sided (20.9% vs 10.8%, p < 0.001) and MSI-H vs. MSS (76.4% vs 9.5%, p < 0.001) cases. In the MSS cases, right-sided had marginally higher frequency of DDR-MT than left-sided (10.6% vs 9.1%, p = 0.055), with much higher frequency of Fanconi anemia pathway alteration in right-sided (1.5% vs 0.7%, p < 0.01). CMS1 subtype had the highest frequency of DDR-MT (34.8%); CMS2 had the lowest (7.1%). DDR-MT cases (vs. DDR-WT) had higher mutation rate of ARID1A (55.0% vs 19.1%, p < 0.0001), PIK3CA (22.6% vs 15.8%, p < 0.0001) and BRAF (20.4% vs 7.3%, p < 0.0001), and lower mutation rate of TP53 (48.2% vs 76.1%, p < 0.0001), APC (60.5% vs 74.5%, p < 0.0001) and KRAS (44.0% vs 49.8%, p < 0.001). Mean TMB was much greater in DDR-MT than DDR-WT (All: 20.9/Mb vs 7.7/Mb, p < 0.0001; MSS: 13.7/Mb vs 7.6/Mb, p < 0.05). PD-L1 positivity was also higher in DDR-MT compared to DDR-WT (All: 10.1% vs 2.7%, p < 0.0001; MSS: 4.8% vs 2.4%, p < 0.0001). Conclusions: Alteration of the DDR pathway was strongly associated with MSI status in CRC. The primary tumor sidedness might also be related, as DDR-MT was more prevalent in right-sided tumors. Elevated TMB and PD-L1 expression in DDR-MT CRC indicate more activated anti-tumor immune profiles compared to DDR-WT, regardless of MSI status, suggesting possible therapeutic benefit from immune checkpoint inhibitors in DDR-MT CRC.

231 Background: Goblet cell carcinoid (GCC) is a distinct subtype of appendiceal neoplasm that exhibits unique clinical and pathologic features. There are a few reports focusing on the molecular differences between GCC and other appendiceal tumors such as adenocarcinoma and neuroendocrine tumor (NET). Methods: A total of 495 appendiceal tumor samples (53 GCCs, 428 adenocarcinomas and 14 NETs) were tested with Next-Generation Sequencing (NGS) on a 592-gene panel and immunohistochemistry (IHC). Microsatellite instability (MSI) / mismatch repair (MMR) status was tested with a combination of NGS, IHC and fragment analysis. Tumor mutational burden (TMB) was evaluated by NGS, and PD-L1 were tested by IHC (SP142). Molecular characteristics of GCCs are compared with those of adenocarcinomas and NETs, using Chi-square test. Results: The top five genes with most frequent mutation rate in GCCs were TP53 (24.0%), ARID1A (15.4%), SMAD4 (9.4%), KRAS (7.5%) and CHEK2 (4.0%). Compared to adenocarcinomas, GCCs showed significantly lower mutation rates in KRAS (7.5% vs 60.4%), GNAS (3.8% vs 34.4%), APC (1.9% vs 11.7%), while significantly higher mutation rates in CDH1 (3.8% vs 0.7%), CHEK2 (4.0% vs 0.3%), CDC73 (2.0% vs 0.0%), ERCC2 (2.0% vs 0.0%) and FGFR2 (1.9% vs 0.0%). Compared to NETs, GCCs showed significantly lower mutation rate in KRAS (7.5% vs 28.6%), APC (1.9% vs 28.6%), BRCA2 (0.0% vs 7.1%) and FANCA (0.0% vs 7.1%), with all p < 0.05. In GCCs, MSI-H/dMMR, TML-high (> 17mut/Mb) and PD-L1 expression were seen in 0.0%, 0.0% and 2.0%, respectively. No significant difference was observed in these immune-related markers’ frequency, compared to adenocarcinomas and NETs. Conclusions: GCCs had considerably distinct mutational profile compared to appendiceal adenocarcinomas and NETs. Understanding these molecular characteristics may be critical for a development of effective treatment strategy in GCC.

227 Background: In cancer patients, an activated coagulation cascade might promote tumor cell dissemination. There are preliminary data suggesting that fibrinogen in combination with platelets can build a meshwork that entraps cancer cells enabling them to escape from immunosurveillance. We therefore hypothesize that variations in genes encoding for regulatory proteins within the coagulation pathway may predict outcome in patients with stage II and III colon cancer. Methods: The impact of three functional single nucleotide polymorphisms (SNPs) within the FGB, SERPINC1 and ITGA2B genes on time to recurrence and overall survival was evaluated in 209 patients with stage II and III colon cancer. Genomic DNA was isolated from formalin-fixed paraffin embedded tissue and the SNPs were analyzed by PCR-based direct sequencing. Results: Baseline characteristics were as follows: median age = 70y (19-91); female/male ratio = 42.8% / 57.2%; 111 patients had stage II, and 98 stage III colon cancer. The FGB rs4220 SNP showed significant association with recurrence rate in the overall population. Patients harboring any A allele had a higher 3-years recurrence rate compared to those with a G/G genotype (28% vs 17%) in both univariate (HR 1.83, 95% confidence interval (CI) 0.99-3.36, p = 0.048) and multivariate analyses (HR 1.94, 95% CI 1.05-3.57, p = 0.034). This trend was most evident among pts with stage II and especially the subgroup of high-risk stage II colon cancer. Again, A allele carriers had a higher 3-years recurrence rate compared to those having a G/G genotype (24% vs 10% and 44% vs 15% respectively) in both univariate (HR 3.32, 95% CI 1.26-8.74, p = 0.010 and HR 5.34, 95% CI 1.38-20.68, p = 0.006) and multivariate analyses (HR 3.34, 95% CI 1.27-8.78, p = 0.015 and HR 5.44, 95% CI 1.40-21.15, p = 0.015). Conclusions: Here, we demonstrate that the FGB polymorphism rs4220 might serve as a prognostic biomarker in stage II colon cancer. Assessment of FGB rs4220 might help us to identify those stage II colon cancer patients who will derive the most benefit from adjuvant chemotherapy.

232 Background: BRD4 plays an important role in transcription, DNA repair and drug resistance. High expression and polymorphisms of BRD4 regulating pathways were reported to be related to worse prognosis in colorectal cancer. Therefore, we hypothesized that genetic variants in BRD4 regulating pathway may predict first-line treatment outcome in mCRC pts. Methods: The impact on outcome of 22 SNPs in 7 genes involved in BRD4 regulating pathway (BRD4, SIPA1, MYC, 53BP1, H2AX, BATF, CD47) was analyzed through the OncoArray, a customized array manufactured by Illumina, on genomic DNA from blood samples of pts enrolled in 2 randomized trials. MAVERICC FOLFIRI/bevacizumab (bev) arm served as discovery cohort (N = 107), FIRE3 FOLFIRI/bev arm as validation (N = 107) and FOLFIRI/cetuximab (cet) arm as control (N = 129). Results: In the discovery cohort, right(R)-sided pts with BRD4 rs4808272 any G allele (N = 46) showed significantly shorter PFS (9.5 vs 18 m) compared to carriers of A/A (N = 21) in both uni- and multi-variable analysis ( p < .01); R-sided pts carrying any T allele of BATF rs7161377 (N = 50) showed longer PFS (12.3 vs 6.8 m) compared to carriers of C/C (N = 14) in univariate analysis ( p < .05) and had a strong trend in multivariable analysis ( p = .06). These findings were all validated in R-sided pts in FIRE3 bev arm (BRD4 rs4808272, PFS 9.8 vs 18.7 m; BATF rs7161377, PFS 15.1 vs 4.2 m) in uni- (both p < .01) and multi-variable ( p = .08 and p < .05 respectively) analysis. No significant association was observed in the control arm. Interestingly, pts carrying CD47 rs3206652 any C allele (N = 13) only showed significant longer PFS (9.0 vs 3.0 m, univariable p < .01 and multivariable p = .07) in the R-sided pts of FIRE3 cet cohort, but no association was observed in the bev-based treatment. Conclusions: Our study demonstrates for the first time that BRD4 and BATF polymorphisms may predict outcomes of bev-based treatment in R-sided mCRC pts; Meanwhile CD47 polymorphism could predict outcomes of cet-based treatment in R-sided mCRC pts. This finding supports a possible role of BRD4 regulating pathway in contributing to resistance to anti-VEGF/EGFR treatment.

418 Background: Alteration of histone modifications participating in transcription and genomic instability, has been recognized as an important role in tumorigenesis. Aberrant expression of histone-lysine N-methyltransferase 2 ( KMT2) family, which methylate histone H3 on lysine 4, is significantly correlated with poor survival in GC. Understanding how gene mutations of KMT2 family interact to affect cancer progression could lead to new treatment strategies. Methods: A total of 1,245 GC were analyzed using next-generation sequencing (NGS) and immunohistochemistry (IHC; Caris Life Sciences, Phoenix, AZ). Tumor mutational burden (TMB) was calculated based on somatic nonsynonymous mutations, and MSI status was evaluated by a combination of IHC, fragment analysis and NGS. PD-L1 status was analyzed by IHC (SP142). Gene fusions were detected by Archer (N = 59) or whole-transcriptome sequencing (N = 129). Results: The overall mutation rate of genes in KMT2 family was 10.6% ( KMT2A: 1.7 %, KMT2C: 4.7%, KMT2D: 7.1%). Overall, the mutation rates were significantly higher in KMT2-mutated (MT) GC than KMT2-wild type (WT) GC, except for TP53 (43% vs 63%, p < .0001). Interestingly, among the genes with significant higher mutation rates in KMT2-MT GC, 28% (21/76) of them were related to DNA damage repair (including BRCA1/ 2, RAD50) and 33% (25/76) of them were related to chromatin remodeling (including ARID1A/ 2, SMARCA4). Overexpression of HER2, amplifications of KRAS, CDK6 and HER2 were significant lower, while PCM1 and BCL3 amplifications were significant higher in KMT2-MT, compared to KMT2-WT GC ( p < .05). Significantly higher prevalence of TMB-high ( > 17mut/MB) (49% vs 3%), MSI-H (53% vs 2%), and PD-L1 overexpression (20% vs 7%) were present in KMT2-MT GC, compared to KMT2-WT GC ( p < .001). The rates of fusions involving ARHGAP26 (19% vs 3%, p < .01)and RELA (29% vs 0%, p < .0001) were significantly higher in KMT2-MT than those in KMT2-WT GC. Conclusions: This is the largest study to investigate the distinct genomic landscape between KMT2-MT and WT GC. Our data indicates that KMT2-MT GC patients could potentially benefit from agents targeting DNA damage repair and immunotherapy, which warrants further in-vitro and in-vivo investigation.

245 Background: HLA-E is an MHC Class I antigen which inhibits NK cell activity by binding to CD94 receptor. Overexpression of HLA-E on crc cells is associated with poor prognostic outcomes and has recently been associated with microsatellite instability. As cet enhances NK cell activity which is dependent on HLAE, this study aims to assess whether differences in HLAE gene expression and polymorphisms lead to different outcomes. Methods: Genomic DNA from blood samples of pts treated with first-line FOLFIRI-cetuximab (cet, n = 129) and FOLFIRI-bevacizumab (bev, n = 107) was genotyped through the OncoArray, a custom array manufactured by Illumina. Gene expression levels were measured from 102 tumor samples of pts in the cet arm by HTG EdgeSeq Oncology Biomarker Panel. PFS and OS outcomes were investigated for an HLAE genetic polymorphism, rs1264457, where G > A leads to glycine > arginine, where glycine has stronger affinity for NK cell receptor. Results: FOLFIRI/cet and FOLFIRI/bev cohort characteristics: median FU (29.1/26.7mo); PFS (12.8/11.5mo); OS (49.8/31.4mo); RAS WT (64%/62%) and RAS mut (15%/16%). Overexpression of HLAE was associated with poor OS (log2 > 13, 30 vs 34 mo) in cet arm (P < .05). No significant association was observed with PFS. Multivariable analysis showed that HLAErs1264457 carriers with any A allele (n = 65) had better PFS than pts with G/G genotype (n = 18) in RAS WT pts treated with FOLFIRI/cet (12.9 vs 12.3 mo; HR = 2.36; 95%CI = 1.14-4.88; p = 0.021). A non-significant trend of improved OS was seen among carriers of A allele than G/G genotype (56.2 vs 40 mo). These effects were not observed in Ras mut pts. No significance was observed in FOLFIRI/bev overall or FOLFIRI/bev RAS WT pts. Conclusions: Overexpression of HLAE leads to poor OS among pts treated with FOLFIRI/cet. Poor PFS was seen among pts treated with cet who are RAS wt carrying polymorphisms allowing for increased binding to NK cell receptor, which in turn enhances HLAE inhibitory function of NK cell lysis. Addition of mAb against HLAE, which have been shown to restore NK cell mediated cell lysis, needs investigation in this pt population.

199 Background: We previously reported that genetic variant in the CCL5/CCR5 pathway predict efficacy of regorafenib in metastatic colorectal cancer patients (mCRC). CCL5 rs2280789 G allele and CCL5 rs3817655 T allele were associated with longer overall survival (OS) and severe skin toxicity due to low VEGF-A production via endothelial progenitor cell (EPC). CCL4 rs1634517 G allele and CCL3 rs1130371 C allele correlated with longer Progression-free survival (PFS) and OS. We investigated the biological role of CCL4 and CCL3 gene polymorphisms. Methods: We analyzed genomic DNA extracted from 79 samples of a Japanese cohort receiving regorafenib. Single nucleotide polymorphisms (SNPs) of genes in CCL5/CCR5 pathway were analyzed by PCR-based direct sequencing. Blood samples were obtained from 57 patients at baseline (BL), day 21 and progressive disease (PD), and serum CCR5, CCR5 ligands (CCL3, CCL4, CCL5) and VEGF-A levels were measured using ELISA. PFS and OS were analyzed using Kaplan-Meier curves and log-rank test. Results: Increased CCL3 levels at PD were associated with longer OS than decreased (12.6 vs 4.8 mos, P = 0.003). Patients with decreased CCL4 levels at day 21 had a trend toward longer PFS and tumor shrinkage. Positive correlation was observed between CCL3 and CCR5 throughout the treatment independent of other ligands (change at day 21: r = 0.426, P = 0.009). There was no significant correlation of CCL3 and CCL4 levels with VEGF-A levels. Patients with the G/G variant in CCL3 rs1130371 had increased CCL3, CCR5 and CCL5 levels at day 21 than any A allele. Similarly, patients with the C/C variant had increased CCL3, CCR5 and CCL5 levels at day 21 compared with those with any A allele. In contrast, both CCL5 rs2280789 G allele and CCL5 rs3817655 T allele were associated with increased CCL3 levels and decreased CCL4 levels at day 21 (P = 0.006, P = 0.043; P = 0.006, P = 0.043). Conclusions: Positive correlation of CCL3, CCR5 and CCL5 impact similarly on CCL3 and CCL4 SNPs, while different manner between CCL3 and CCL4 was found in CCL5 SNPs. This suggests an alternative mechanism of action in the network of CCR5 and the ligands except CCL5-VEGF-A signaling via EPC in mCRC patients receiving regorafenib.

170 Background: Germline polymorphisms in CCR5 have been associated with treatment outcome in pts with mCRC receiving regorafenib and cetuximab-based treatment. CCR5 Δ32, a loss of function deletion, plays a key role in infectious diseases but data in CRC are scarce. We tested whether CCR Δ32 and CCR5 gene expression may be associated with outcome in mCRC pts receiving first-line treatment. Methods: The impact of CCR5 Δ32 was evaluated in 614 pts enrolled in the randomized FIRE-3 trial (FOLFIRI/cetuximab, cet, n = 313; FOLFIRI/bevacizumab, bev, n = 301). Gene expression was evaluated in 102 pts in the FOLFIRI/cet arm from FIRE-3 and 155 pts treated in the MAVERICC trial (FOLFIRI/bev, n = 76; FOLFOX6/bev, n = 79) from tumor tissue by HTG EdgeSeq Oncology Biomarker Panel and NanoString expression panel, respectively. The association between CCR5 Δ32 and clinical outcomes was evaluated using Cox regression and log-rank tests. Gene expression was dichotomized using an optimal cutoff and P-values computed using a permutation-based approach. Results: In FIRE-3, CCR5 Δ32 was significantly associated with worse PFS in patients with right-sided tumors (RT) receiving FOLFIRI/cet (n = 32; median PFS 3.41 vs 7.84 mo; HR 4.39, 95%CI 1.12-17.24; P= .022;). These associations were not observed in left-sided tumors or pts treated with bev. Lower levels of CCR5 expression trended to be associated with shorter PFS and OS in the same subgroup of RT treated in the cet arm ( P= .096 and P= .063 for PFS and OS, respectively). Lower CCR5 expression was associated with longer PFS in pts treated with FOLFIRI/bev in the MAVERICC trial, regardless of tumor side (mPFS 17.91 vs 11.04 mo; P= .03). A significant interaction between the impact of CCR5 expression levels on PFS and chemotherapy backbone was observed ( P= .019). Low CCR5 expression was associated with worse PFS in pts with RT treated with oxaliplatin (11.10 vs 13.80 mo; P= 0.023). Conclusions: Our results provide the first evidence that CCR5 Δ32 and CCR5 gene expression levels may predict outcomes in mCRC pts receiving first-line treatment with a differential effect depending on tumor location, biologic agent and chemotherapy backbone.

187 Background: ICD is an immune response against dead-cell antigens from cancer cells treated with cytotoxic and/or targeted therapies. Oxaliplatin (OHP) and cetuximab (Cet) are distinct drugs to elicit ICD, while most other anticancer agents kill cancer cells in a nonimmunogenic manner. We hypothesized that genetic variants in ICD-related genes could predictive efficacy of OHP and/or Cet in mCRC. Methods: We analyzed data of mCRC patients enrolled in three 1st-line randomized trials [FIRE-3: FOLFIRI+Cet vs FOLFIRI+bevacizumab (Bev), TRIBE: FOLFOXIRI+Bev vs FOLFIRI+Bev and MAVERICC: FOLFOX+Bev vs FOLFIRI+Bev]. Genomic DNA from blood samples was genotyped through the OncoArray, a custom array manufactured by Illumina. Candidate 14 SNPs in five ICD-related genes ( CALR, HMGB1, ANXA1, LRP1 and P2RX7) were tested for association with progression-free survival (PFS) and overall survival (OS), using Cox proportional hazards model. We tested treatment-by-SNP interactions in the following cohorts: combined TRIBE and MAVERICC (OHP-containing treatment vs non-OHP-containing treatment), and FIRE-3 (FOLFIRI+Cet vs FOLFIRI+Bev). An interaction p-value (i p) < 0.05 was considered significant. Results: Totally, 890 patients’ SNPs were available (FIRE-3: n = 236, TRIBE: n = 324, and MAVERICC: n = 330). In the combined TRIBE and MAVERICC cohorts [the reference of hazard ratio (HR) is non-OHP-containing treatment], a significant interaction was observed in ANXA1 rs1050305 (A/A: HR 0.96, Any G: HR 2.62, i p < 0.01), LRP1 rs1466535 (G/G: HR 1.39, Any A: HR 0.91, i p = 0.02), P2RX7 rs2230911 (C/C: HR 0.98, Any G: HR 1.76, i p = 0.03) and P2RX7 rs208294 (C/C: HR 1.82, Any T: HR 0.93, i p < 0.01) on OS. For PFS, that was observed in CALR rs110222 (G/G: HR 1.30, Any A: HR 0.87, i p = 0.02), HMGB1 rs1045411 (C/C: HR 0.85, Any T: HR 1.30, i p = 0.04) and HMGB1 rs1360485 (T/T: HR 0.81, Any C: HR 1.40, i p < 0.01). However, in the FIRE-3 cohort, no significant interactions were observed in any SNPs. Conclusions: Our results showed for the first time that SNPs in ICD-related genes may predict efficacy of OHP-containing treatment in mCRC. But the predictive values for Cet efficacy was not evident.

190 Background: Wnt signaling deregulation is a primary driver of colorectal carcinogenesis. RNF43 is a key suppressor of Wnt activation while R-Spodin inhibits RNF43 activity. RNF43 mutations are associated with the serrated neoplasia pathway, BRAF mutation and MSI. We hypothesized that genetic variants in the R-Spodin/RNF43 complex and corresponding genes expression levels may predict cetuximab efficacy in mCRC pts. Methods: Genomic DNA from blood samples of pts enrolled in the randomized FIRE-3 trial was genotyped through the OncoArray, a custom array manufactured by Illumina. The impact on outcome of 17 functional SNPs within RNF43/ ZNRF3, LGR4/5 and RSPO1/2/3 was analyzed in 129 pts treated with first-line FOLFIRI/cet and 107 pts treated with FOLFIRI/bevacizumab (bev). Gene expression levels were measured from tumor tissue samples from 102 pts in the cet arm by HTG EdgeSeq Oncology Biomarker Panel. False discovery rate (FDR) for gene expression analysis was computed using the Benjamini-Hochberg approach (significant Q < 0.1). Results: In the cet cohort, pts with the C/C genotype of ZNRF3 rs132531 had significantly shorter overall survival compared to any T allele carriers (mOS: 20.3 vs 52 mo) in both univariable (HR 3.61, 95% CI 1.65-7.88, P < .001) and multivariable analysis (adjusted P = .01). Conversely, RSPO1 rs4652964 any G allele carriers showed increased tumor response (TR) rates compared to the A/A genotype (83 vs 66 %, P = .04). These associations were not observed in bev arm. Lower gene expression levels of RNF43 were associated with shorter PFS in pts with right-sided tumors receiving FOLFIRI/cet ( P = .006, Q < 0.1). RSPO1 expression levels were also associated with TR in the same subgroup (70 vs 10% in high vs low; P = .001, Q < .05). RNF43 expression was associated with TR in pts with left-sided tumors (82% in high vs 58% in low, P = .014, Q = 0.1). Conclusions: Our results provide the first evidence that germline polymorphisms and tumor gene expression levels of RNF43/ ZNRF3 and RSPO1 may have a predictive value in mCRC pts receiving first-line cetuximab-based treatment and contribute to modulate anti-EGFRs activity.

479 Background: Isocitrate dehydrogenases (IDH) play a key role in energetic metabolism and IDH mutations (mut) promote oncogenesis via epigenetic and genetic changes. Data addressing the molecular contexture of IDH1/2 mut in BC are lacking. We aimed to characterize the molecular profile of IDH1/2 mutant (mIDH) GI cancers with a focus on BC. Methods: 27954 GI cancer samples collected between August 2000 and July 2019 were included: 2057 BC (1159 ICC, 277 extrahepatic CC, 573 gallbladder, 48 unspecified CC), 13807 colorectal, 4183 gastric/esophageal, 3060 other. Samples were analyzed using NextGen DNA sequencing, in situ hybridization, RNA sequencing and immunohistochemistry (Caris Life Sciences, Phoenix, AZ). Tumor mutational burden (TMB) was calculated based on somatic nonsynonymous missense mut. MMR/MSI status was evaluated by a combination of IHC, Fragment Analysis and NGS. Results: mIDH frequency in BC was 10.3% (211/2057), with higher prevalence of IDH1 mut (8.2%). ICC showed the highest mut prevalence: IDH1 13.5%, IDH2 4%. Mut rates in other GI cancers types were < 1%, except for HCC (1.9%, 11/582) and small bowel (1.1%, 8/736). When compared to IDH wild type (WT), mIDH BC showed lower mut rates in TP53 (13 vs 43%), KRAS (8 vs 19%), CDKN2A (1 vs 9%), and SMAD4 (0 vs 9%), whereas PBRM1 mut were higher (14 vs 5%) ( P < .001 for all comparisons). There was a trend towards higher frequency of ARID1A and BAP1 in mIDH BC. HER2 expression and amplification rates were lower in mIDH vs WT BC (0.5 vs 3%, P = .048 and 0 vs 6%, P = .002). FGFR2 fusion was detected in 7% of WT vs 2% of mIDH BC. mIDH BC showed a lower TMB (0.7 vs 3.7%, P = .048) and a trend for lower MSI rates (0.6 vs 3%, P = .06) vs WT BC. Conversely, IDH mut were associated with higher TMB and MSI ( P < .001) and higher PD-L1 expression in other GI cancers. Conclusions: This is the largest and most extensive profiling study to investigate the molecular makeup of mIDH BC and GI tumors. Our data show distinct gene alteration patterns characterizing mIDH BC, involving genes related to chromatin remodeling and DNA repair, and a differential expression of immune related markers compared to other mIDH GI tumors. These findings can contribute to the development of rational combination therapies and to improved patient selection in the future.

3545 Background: RNA binding proteins (RBPs) post-transcriptionally regulate gene expression by stabilizing or destabilizing target messenger RNA. Although alteration of RBPs affects many steps of cancer development, its clinical implication in mCRC remains unclear. Methods: We analyzed data from mCRC patients (pts) enrolled in three first-line randomized trials (FIRE-3, TRIBE, and MAVERICC). Genomic DNA from blood samples of pts was genotyped through the OncoArray, a custom array manufactured by Illumina. Candidate 30 SNPs in 10 RBP genes (MSI1, MSI2, ELAVL1, RBM3, LIN28A, LIN28B, IGF2BP1, IGF2BP2, IGF2BP3, ZFP36) were tested on association with progression-free survival (PFS) and overall survival (OS). To evaluate prognostic effects and heterogeneities across treatment arms, meta-analysis approach using the METASOFT software was conducted. We also tested interaction between each SNP and treatment within each trial, i.e. FIRE-3 cohort (FOLFIRI+cetuximab (Cet) vs FOLFIRI+bevacizumab (Bev)) and MAVERICC cohort (FOLFIRI+Bev vs FOLFOX6+Bev). For multiple testing, p values were adjusted by the false discovery rate (FDR) method. Results: A total of 884 pts’ SNPs data were available (FIRE-3: n = 236, TRIBE: n = 324, and MAVERICC: n = 324). Meta-analysis combining three trials showed RBM3 rs926152 (adjusted p = 0.045) and RBM3 rs2249585 (adjusted p = 0.016) were significantly prognostic for PFS. Whereas, in terms of OS, only LIN28B rs314277 (adjusted p = 0.045) was significant, and RBM3 rs926152 (adjusted p = 0.057) and RBM3 rs2249585 (adjusted p = 0.059) had a trend. Interaction test showed several SNPs were potentially predictive (raw p < 0.05), although without any significance after FDR adjustment: in FIRE-3 cohort, MSI2 rs1822381, RBM3 rs926152, LIN28B rs221635, IGF2BP1 rs2969 for OS; in MAVERICC cohort, MSI1 rs1179442 and MSI2 rs3826301 for OS, ELAVL1 rs4804244 for PFS. Conclusions: Our results indicate prognostic potential of SNPs in RBP genes, such as RBM3 and LIN28B, in mCRC. However, we find no distinct evidence that these SNPs can predict differential effect between Cet and Bev, or between oxaliplatin- and irinotecan-based chemotherapy.

3145 Background: BRCA muts in CRC are associated with a higher tumor mutation burden irrespective of microsatellite instability, which highlights the possibility of using PARP-inhibitors(i) in CRC in the future. Early phase studies have shown that combination of PARP-i with oxaliplatin or irinotecan enhances tumor lysis in CRC. In this study, we investigated the influence of mutations in the Homologous Repair Pathway genes on survival outcomes among mCRC pts treated with oxaliplatin or irinotecan-based regimens. Methods: The impact of selected SNPs within 4 genes (BRCA1, BRCA2, RAD51, BARD1) on OS/PFS was analyzed through the OncoArray, a custom array manufactured by Illumina, on genomic DNA from blood samples of 431 pts enrolled in 2 randomized trials. TRIBE FOLFIRI/bev arm (n = 215, mPFS/OS: 9.7/26.2 mo) served as discovery cohort, FIRE-3 FOLFIRI/bev arm (n = 107, mPFS/OS: 11.5/31.4 mo) as validation and TRIBE FOLFOX/bev arm (n = 109, mPFS/OS: 10.8/26 mo) as control. Results: Significant associations were found among carriers of BRCA1 rs8176318 SNP, where C > A base change is known to reduce BRCA1 expression among CRC cells. In the discovery cohort, pts with A/A had shorter OS (22.4 vs 27.3 mo, P = .009) and PFS (7.5 vs 10.5 mo, P = .0006) compared to carriers of any C allele in both univariate and multivariate analysis. Same results were observed in pts with left-sided CRCs (PFS-7.5 vs 11 mo, P = .005; OS- 25.6 vs 32.3, P = .034) and among males (PFS- 7.5 vs 10.3 mo, P = .008; OS- 25.7 vs 31.3 mo, P = .008) in both uni and multivariate analysis. These results were also seen in the validation cohort: A/A carriers in left-sided CRCs had poor OS (26.1 vs 36.0 mo, P = .027) and PFS (9.5 vs 11.7 mo, P = .002. Males with A/A genotype also had poor OS (24.7 vs 32.5 mo, P = .028) and PFS 96.9 vs 12.2 mo; P = .0002). In the control cohort, A/A genotype carriers had poor tumor response in overall (P = .011) and left-sided disease (P = .034). These outcomes were independent of KRAS mutation status. No significant relationship was observed among females with mCRC. Conclusions: This is the first study to report that BRCA1 mut influence survival outcomes among mCRC pts, particularly among males and those with left-sided disease. Prospective trials are warranted to assess the utility of routine BRCA mut testing and the role of PARP-i in improving survival outcomes in this pt population.

3595 Background: PD is one of the most common age-related neurodegenerative disorders. Large epidemiological studies have consistently reported a reduced risk of CRC in PD patients (pts), but the biology behind this evidence is unclear. The methylation status of SNCA, one of the causal PD genes, has been identified as a tool for CRC screening and early diagnosis when detected in stool samples, and alterations in core PD genes are prevalent across human malignancies including CRC. Methods: The impact on outcome of 13 SNPs within 6 core PD genes ( SNCA, PRKN, UCHL1, PINK1, DJ-1, LRRK2) was analyzed in pts enrolled in the randomized FIRE-3 trial. Genomic DNA from blood samples of pts treated with first-line FOLFIRI-cetuximab (cet, n = 129) and FOLFIRI-bevacizumab (bev, n = 107) was genotyped through the OncoArray, a custom array manufactured by Illumina. Gene expression levels were measured from 102 tumor samples of pts in the cet arm by HTG EdgeSeq Oncology Biomarker Panel. Results: In the cet cohort, pts carrying the G/G variants of SNCA rs356165 and rs2736990 had significantly shorter mOS (30 vs 41.1 mo) compared to any A genotype in both uni- and multivariable analysis (adjusted P[ Padj] = .047 and .042, respectively). LRKK2 rs3761863 T/T allele carriers showed shorter mPFS (9.5 vs 13.3 mo, Padj = .01), while rs11564148 any A carriers had longer mPFS (14.2 vs 10.2 mo, Padj = .01) compared to reference genotypes. LRKK2 rs11564148 any A carriers also showed longer mOS in multivariable analysis (43.7 vs 33.2 mo, Padj = .044). Any C allele carriers of PINK1 rs1043424 showed longer mPFS in uni- and multivariable analysis ( Padj < .001). No significant interaction was found with gender, tumor location and RAS status. These associations were not observed in bev arm. High SNCA expression was associated with worse mPFS (log2 > 7.89, 5.9 vs 11.2 mo) and mOS (log2 > 7.68, 17.9 vs 31.1 mo) in FIRE-3 cet arm ( P < .05). Conclusions: We provide the first evidence that gene expression and genetic variants in PD genes may have a predictive value in mCRC pts receiving first-line cetuximab-based treatment. Our findings open new perspectives on the role of PD genes in CRC biology warranting further investigation.

2633 Background: T-cell activation plays a key role in maintaining an effective host immunity and antitumor control. Targeting costimulatory immune checkpoint proteins can lead to increased antitumor immunity. We hypothesize, that variations in genes encoding for T-cell activation molecules may predict outcome in stage II and III colon cancer patients. Methods: The impact of 4 functional single nucleotide polymorphisms (SNPs) within the LIGHT, ICOS, CD80 and GITR genes on time to recurrence and overall survival was evaluated in 209 patients with stage II and III colon cancer. Genomic DNA was extracted from formalin-fixed paraffin embedded tissue and the SNPs were analyzed by PCR-based direct sequencing. Results: Baseline characteristics were as follows: median age = 70y (19-91); female/male ratio = 41.6% / 58.4%; 111 patients had stage II, and 98 stage III colon cancer. The LIGHT rs3760746 SNP showed significant association with recurrence rate in the overall population. Patients harboring any G allele had a lower 3-years recurrence rate compared to those with a A/A genotype (16% vs 30%) in both univariate (HR 0.53, 95% Confidence intervall (CI) 0.29-0.96, p = 0.033) and multivariate analyses (HR 0.52, 95% CI 0.29-0.95, p = 0.034). This trend was most evident among patients with stage III colon cancer. Here again, G allele carriers had both a lower 3-years recurrence and a longer 5-years overall survival rate compared to those having a A/A genotype (21% vs 40% and 77% vs 43%) in both univariate (HR 0.42, 95% CI 0.19-0.90, p = 0.021 and HR 0.51, 95% CI 0.25-1.03, p = 0.046) and multivariate analyses (HR 0.43, 95% CI 0.20-0.93, p = 0.033 and HR 0.30, 95% CI 0.14-0.65, p = 0.002). Conclusions: Our results provide the first evidence that polymorphisms within the T-cell costimulatory LIGHT gene might serve as prognostic markers in patients with stage II and III colon cancer. Targeting LIGHT might be a promising approach to further optimize treatment options and to improve outcome of colon cancer patients in the adjuvant setting.

3048 Background: Strong evidence supports the critical role of the gut-brain axis in modulating gastrointestinal function and homeostasis. Available data suggest an involvement of the dopaminergic pathway in CRC dynamics. DA could inhibit proliferation and migration of tumor endothelial cells and enhanced 5-fluorouracil efficacy in CRC preclinical models. Hence, we hypothesized that genetic variants in DA signaling may predict treatment outcomes in mCRC pts. Methods: The impact on outcome of 22 selected single nucleotide polymorphisms (SNPs) in 9 genes of the DA signaling pathway ( DRD1, DRD2, DRD3, DRD4, DRD5, TAAR1, SLC6A3, SLC18A2, PPP1R1B) was analyzed on a total of 884 pts enrolled in three independent randomized first-line trials: TRIBE (n = 324), MAVERICC (n = 324), and FIRE-3 (n = 236). Genomic DNA from blood samples of pts was genotyped through the OncoArray, a custom array manufactured by Illumina. A meta-analysis approach using the METASOFT software was used to quantify SNPs prognostic effects and heterogeneities across treatment arms. P values were adjusted for multiple testing using the false discovery rate (FDR) method. Results: Overall, DRD3 rs3732790, rs9817063 and rs2134655 showed a significant nominal p value ( P) in association with tumor response (TR) across trials ( P= 0.032, P= 0.021, P= 0.027, respectively). TAAR1 rs8192620 showed an association with both progression free survival (PFS) ( P= 0.01) and overall survival (OS) ( P= 0.033), similar to DA transporter SLC6A3 rs6347 ( P= 0.016 and P= 0.002, respectively). SLC6A3 rs6347 association with OS remained significant after FDR ( PFDR= 0.045). Subgroup analyses showed a significant association with PFS for DRD1 rs267410 and SLC6A3 rs2652510 in females ( PFDR= 0.056), and between SLC6A3 rs6347 and OS ( PFDR= 0.041) and SLC6A3 rs6876890 and TR ( PFDR= 0.05) in KRAS wild type. Conclusions: Our results suggest that SNPs in DA signaling may have a prognostic value in mCRC pts receiving first-line treatment. Upon validation, these findings may provide novel insight on the role of DA signaling in CRC and possibly contribute to open novel therapeutic perspectives.