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Backgrounds Low-pass whole-genome sequencing (LP-WGS)-based circulating tumor DNA (ctDNA) analysis is a versatile tool for somatic copy number aberration (CNA) detection, and this study aims to explore its clinical implication in breast cancer. Methods We analyzed LP-WGS ctDNA data from 207 metastatic breast cancer (MBC) patients to explore prognostic value of ctDNA CNA burden, and validated it in 465 stage II-III triple-negative breast cancer (TNBC) patients who received neoadjuvant chemotherapy in phase III PEARLY trial (NCT02441933). The clinical implication of locus-level LP-WGS ctDNA profiling was further evaluated. Results We found that a high baseline ctDNA CNA burden predicts poor overall survival and progression-free survival of MBC patients. The post-hoc analysis of PEARLY trial showed that a high baseline ctDNA CNA burden predicted poor disease-free survival independent from pathologic complete response (pCR), validating its robust prognostic significance. The 24-month disease-free survival rate was 96.9% and 55.9% in pCR (+)/Low I-score and non-pCR/High I-score patients, respectively. The locus-level ctDNA CNA profile classified MBC patients into five molecular clusters and revealed targetable oncogenic CNAs. LP-WGS ctDNA and in vitro analysis identified the BCL6 amplification as a resistance factor for CDK4/6 inhibitors. We estimated ctDNA-based homologous recombination deficiency (HRD) status of patients by shallowHRD algorithm, which was highest in the TNBC and correlated with platinum-based chemotherapy response. Conclusions These results demonstrate LP-WGS ctDNA CNA analysis as an essential tool for prognosis prediction and molecular profiling. Particularly, ctDNA CNA burden can serve as a useful determinant for escalating or de-escalating (neo)adjuvant strategy in TNBC patients.

Ras protein has been considered a fascinating target for anticancer therapy because its malfunction is closely related to cancer. However, Ras has been considered undruggable because of the failure to regulate its malfunction by controlling the Ras activation mechanism. Recently, Lumakras targeting the G12C mutation was approved, and therapeutic interest in Ras for anticancer therapy has been rejuvenated. Here, we present a series of compounds that inhibit Ras via a unique mechanism of action that exploits the relationship between the Wnt/β-catenin pathway and Ras. KYA1797K (1) binds to axin to stabilize the β-catenin destruction complex that causes the phosphorylation and subsequent degradation of Ras, similar to canonical β-catenin regulation. Based on the chemical structure of 1, we performed a structural optimization and identified 3-(2-hydroxyethyl)-5-((6-(4-nitrophenyl)pyridin-2-yl)methylene)thiazolidine-2,4-dione (13d) as the most potent compound. 13d displayed antitumor effects in a colorectal cancer model with enhanced inhibition activity on Ras. The results of this study suggest that the further development of 13d could contribute to the development of Ras inhibitors with novel mechanisms of action.

Pancreatic cancer is a major malignant tumor without an effective treatment. KRAS mutations occur in 90% of the pancreatic cancer patients and are a major obstacle for treatment of pancreatic cancer. Pancreatic cancer patients have been treated with limited chemotherapeutic agents such as gemcitabine. However, patients often develop resistance to gemcitabine that is attributed to KRAS mutations. Gemcitabine treatment activates both the Wnt/β-catenin and RAS/ERK pathways. These signaling pathways are also activated in the gemcitabine-resistant pancreatic cancer cell lines, suggesting that they play an important role in gemcitabine resistance in pancreatic cancer. The gemcitabine-resistant cell lines show enhanced migratory and invasive capabilities than their parental lines. Therefore, we investigated the effects of a small molecule, KYA1797K that degrades both β-catenin and RAS, on pancreatic cancer. KYA1797K decreased the expression level of both β-catenin and KRAS in pancreatic cancer cell lines expressing either wild-type or mutant KRAS. It also suppressed migration and invasion of gemcitabine-resistant and parental pancreatic cancer cells. Overall, we demonstrated that inhibiting the Wnt/β-catenin and RAS/ERK pathways by destabilizing β-catenin and RAS could be a therapeutic approach to overcome gemcitabine resistance in pancreatic cancer.

A patient-derived organoid (PDO) is an in vitro three-dimensional model which shows similar features in phenotypic and genetic aspects with primary tissue from patients. PDOs are useful for preclinical studies including drug sensitivity tests of tumors from individual patients as well as development of novel targeted agents. Collectively, PDOs are recently introduced as an emerging platform for personalized medicine. We obtained a total of 100 surgical specimens from 100 patients with breast cancer at the Yonsei Cancer Center, Severance Hospital, Seoul, Korea. One of the tissue specimens was acquired from a breast cancer patient-derived xenograft model. We dissociated the tissues and isolated breast cancer primary tumor cells from the samples, and then the cells were cultured in basement membrane-like matrix in 3D manner with growth medium with supplements. We defined successful establishment of PDOs as continuous growth after 3 passaging. Among all 100 cases, 32 cases failed to culture or passage, however, 41 cases were successfully cultured over 3 passages. In addition, the remaining 27 cases are still in progress of establishment. Success rate of PDO was 68% (68/100). Subtypes of primary tumors of the PDO were 33.8% (23/68) of luminal A, 26.5% (18/68) of luminal B, 26.5% (18/68) of triple-negative, 5.9% (4/68) of triple-positive and 7.4% (5/68) of HER2-enriched. Success rates of each subtype were 69.7% (23/33) of luminal A, 72.0% (18/25) of luminal B, 66.7% (18/27) of triple-negative, 66.7% (4/6) of triple-positive and 55.6% (5/9) of HER2-enriched. Pathologic evaluation using immunohistochemistry revealed that PDOs showed similar morphologic and immunohistochemical features with primary tumors. The selective sensitivity of PARP inhibitor, olaparib, was confirmed in PDOs harboring mutant BRCA1/2 compared with BRCA1/2 wild-type PDOs. Overall, PDOs can be used as a real-time platform for drug sensitivity and screening analyses, and a robust tool for preclinical studies in breast cancer. Citation Format: Won-Ji Ryu, Shinyoung Park, Jeong Dong Lee, Yumi Hwang, Seongyeon Jo, Kweon Tae Yong, Ja Seung Koo, Min Hwan Kim, Joo Hyuk Sohn, Hyung Seok Park. Establishment of patient-derived organoid of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 178.

BRCA1 L1780P BRCT domain mutation has been recognized as a pathogenic mutation in patients with breast cancer. However, the molecular significance of this mutation has not yet been studied in triple-negative breast cancer (TNBC) cells in vitro. We established MDA-MB 231, HCC1937, and HCC1395 TNBC cell lines expressing BRCA1 L1780P mutant. BRCA1 L1780P mutant TNBC cells showed increased migration and invasion capacity, as well as increased sensitivity to olaparib and carboplatin compared to BRCA1 wild-type cells. BRCA1 L1780P mutant TNBC cells showed decreased RAD51 expression and reduced nuclear RAD51 foci formation following carboplatin and olaparib treatment. The molecular interaction between p-ATM and BRCA1 was abrogated following introduction of BRCA1 L1780P mutant plasmid in TNBC cells, suggesting that the BRCA1 L1780P mutation disrupts the p-ATM-BRCA1 protein-protein interaction. We established an olaparib-resistant BRCA1 L1780P mutant TNBC cell line by chronic drug treatment. Olaparib-resistant cell lines showed upregulation of RAD51 expression upon olaparib treatment, and reduction in RAD51 expression in olaparib-resistant cells restored olaparib sensitivity. Collectively, these results suggest that the BRCA1 L1780P mutation impairs RAD51 recruitment by disrupting p-ATM-BRCA1 interaction, which is a crucial molecular factor in homologous recombination and olaparib sensitivity. Further therapeutic targeting of RAD51 in BRCA1 L1780P mutant breast cancer is warranted.

Triple-negative breast cancer (TNBC) is one of the most heterogeneous diseases in solid tumors and has limited therapeutic options. Due to the lack of appropriate targetable markers, the mainstay therapeutic strategy for patients with TNBC has been chemotherapy for the last several decades. Indeed, TNBC tumors have no expression of estrogen receptor, progesterone receptor, or human epidermal growth factor receptor 2 (HER2); therefore, they do not respond to hormone therapy and HER2-targeted therapy. In this review paper, the molecular heterogeneities, possible therapeutic targets, and recently approved and upcoming drugs for TNBC will be summarized.

Background Previous studies proposed low-pass whole genome sequencing (LP-WGS)-based circulating tumor DNA (ctDNA) analysis as a versatile tool for genomic profiling and therapeutic monitoring of cancer patients. Here we demonstrate LP-WGS ctDNA genomic profiles and its clinical significance in metastatic breast cancer patients. Patients and methods This prospective exploratory study enrolled 207 treatment-naïve metastatic breast cancer patients from Feb 2017 to September 2020 in Yonsei Cancer Center. The median follow-up duration of patients was 35 months. The baseline (n=207) and post-progression (n=48) plasma samples were prospectively collected on first-line systemic therapy, and LP-WGS was employed for ctDNA somatic copy number alteration (CNA) analysis. The CNA burden of ctDNA was scored by “I-score” method, which was developed to measure genome-wide chromosomal instabilities, to be matched with therapy response. The unsupervised molecular clustering and homologous recombination deficiency (HRD) estimation by shallowHRD algorithm were performed using locus-level CNA profiles with 1 mega base pair resolution. Results The baseline I-score ctDNA CNA burden was highest in triple-negative breast cancer (TNBC) patients among subtypes, and the patients were dichotomized by median I-score level 5.54 (range 2.55 to 12.98). The high baseline ctDNA I-score was independently associated with poor overall survival (hazard ratio [HR] = 3.98, p < 0.001) with adjustment of tumor subtype, visceral metastasis, and disease status (de novo stage IV versus recurrent). The progression-free survival (PFS) on endocrine plus CDK4/6 inhibitors (HR = 2.75, p = 0.005), anti-HER2 therapy (HR = 2.52, p = 0.032), and cytotoxic chemotherapy (HR = 2.33, p = 0.012) was also shorter in high baseline I-score patients than in low I-score patients. The locus-level CNA profile was analyzed in high I-score patients (n=103), and the patients were classified into five molecular clusters with distinct overall survival by unsupervised k-means clustering of CNA profile: basal-like, EGFR-high basal-like, CCND1-high, luminal, and HER2-enriched clusters. Patients with BCL6 (p = 0.009) and PIK3CA amplification (p < 0.001) on baseline ctDNA showed significantly shorter PFS on CDK4/6 inhibitor treatment. The matched baseline and post-progression ctDNA analysis found emergence of FGFR1 amplification and MYC amplification after CDK4/6 inhibitor treatment (n=1, each). The ctDNA shallowHRD score was highest in TNBC patients among subtypes, and TNBC patients with high shallowHRD score (≥10) showed high response rate on (58.3% versus 28.6%) on platinum-based chemotherapy. Conclusion LP WGS-based ctDNA analysis provides a robust tool for non-invasive genomic clustering, therapy response prediction, and HRD estimation in metastatic breast cancer patients. All patients (n=207)Low I-score (n=104)High I-score (n=103)N (%)N (%)N (%)Age, Median (Interquartile range)54 (46-62)53 (47-60)54(44-62)GenderFemale205 (99)102 (98.1)103Male2 (1)2 (1.9)0SubtypeHR+ HER2-106 (51.2)61 (58.7)45 (43.7)HR- HER2+33 (15.9)14 (13.5)19 (18.4)HR+ HER2+22 (10.6)11 (10.6)11 (10.7)HR- HER2- (TNBC)46 (22.2)18 (17.3)28 (27.2)Disease statusDe novo stage IV74 (35.7)31 (29.8)43 (41.7)Recurrent133 (64.3)73 (70.2)60 (58.3)Primary therapyEndocrine + CDK 4/6 inhibitor97 (46.9)55 (52.9)42 (40.8)Anti-HER2 based therapy54 (26.1)24 (23.1)30 (29.1)Chemotherapy45 (21.7)16 (15.4)29 (28.2)Others11 (5.3)9 (8.7)2 (1.9)Visceral metastasisYes142 (68.6)60 (57.7)82 (79.6)No65 (31.4)44 (42.3)21 (20.4)Metastasis SitesLung89 (43)43 (41.3)46 (44.7)Brain19 (9.2)4 (3.8)15 (14.6)Liver59 (28.5)13 (12.5)46 (44.7)Bone120 (58)47 (45.2)73 (70.9)Lymph node90 (43.7)32 (30.8)58 (56.9)Pleura33 (15.9)17 (16.3)16 (15.5) Citation Format: Joohyuk Sohn, Min Hwan Kim, Jin Mo Ahn, Won-Ji Ryu, Seul-Gi Kim, Jee Hung Kim, Tae Yeong Kim, Hyun Ju Han, Jee Ye Kim, Hyung Seok Park, Seho Park, Byeong Woo Park, Seung Il Kim, Eun Hae Cho, Gun Min Kim. Whole genome sequencing-based circulating tumor DNA profiling of metastatic breast cancer patients for molecular characterization and therapy response prediction [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD6-07.

Background The molecular selective pressure on anti-tumor therapy drives lineage plasticity in several cancer types to develop drug resistance. The subtype conversion from luminal to triple-negative breast cancer (TNBC) subtype fuels endocrine resistance and disease aggressiveness. In this study, we analyzed mechanisms of luminal to basal subtype conversion by clinical sample sequencing and molecular study. Method We performed whole-exome sequencing (WES) of primary and metastatic tumor tissues from breast cancer patients with luminal to basal [from HR(+)/HER2(-) to TNBC] subtype conversion (experimental, n=14) and patients with subtype maintenance (luminal to luminal subtype, control, n= 36) after adjuvant endocrine therapy. For RNA-sequencing, the subset of patients (experimental, n=14; control n=7) was further analyzed. The differences in genetic alterations and gene expression were compared between two patient groups to identify genetic predictors of subtype conversion. We also manipulated genetic factors related to subtype conversion in MCF7 cells to identify molecular signaling to drive lineage change. Results In WES analysis, TP53 mutation was more frequently observed in luminal breast cancer patients with subtype conversion to TNBC [60% (12 out of 20 tissues in experimental group) versus 20% (8/40 tissues in control group)]. Whereas, GATA3 mutations were only observed in patients of subtype maintenance (0% versus 20%), and the mRNA level of GATA3 was downregulated after luminal-to-basal conversion. The TP53 and GATA3 mutations were both observed in the matched primary and metastatic tissues, suggesting that these mutations predisposed subtype conversion but were not acquired during the adjuvant endocrine therapy. In expression signature analysis, the patients with subtype conversion showed the upregulation of KRAS signaling and the suppression of GATA3 signature in metastatic TNBC tumors compared to primary luminal tumors. In primary tumors, RELA and MYC signatures were only upregulated in tumors that underwent subtype conversion later. We found ESR1 expression was decreased by knockdown of TP53 and GATA3 in MCF7 cells. The knockdown of TP53 and GATA3 also induced basal marker expressions, cytokeratin 5 and 14, in MCF7 cells. ESR1 expression and luminal markers were also decreased by GATA3 suppression in T47D harboring TP53 mutation. Conclusion In luminal-type breast cancer, the subtype conversion is the one of the major obstacles for their treatment and preventing recurrence. We found the genetic alterations of TP53 mutation was the key predisposing factor of luminal to basal subtype conversion, whereas GATA3 mutation is a protecting factor for subtype conversion in luminal breast cancers. Thus, targeting TP53-GATA3 axis would be a potential therapeutic strategy to overcome endocrine resistance and block the subtype conversion in luminal type breast cancer. Citation Format: Won-Ji Ryu, Hyun-Yi Kim, Tae Yeong Kim, Yeona Choi, Hyun Ju Hahn, Seul-Gi Kim, Gun Min Kim, Ja Seung Koo, Seung Il Kim, Joohyuk Sohn, Min Hwan Kim. TP53-GATA3 mutation status predisposes luminal-to-basal subtype conversion in advanced breast cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6082.

BRCA1 L1780P BRCT domain mutation has been recognized as a pathogenic mutation in patients with breast cancer. However, the molecular significance of this mutation has not yet been studied in triple-negative breast cancer (TNBC) cells in vitro. We established MDA-MB 231, HCC1937, and HCC1395 TNBC cell lines expressing BRCA1 L1780P mutant. BRCA1 L1780P mutant TNBC cells showed increased migration and invasion capacity, as well as increased sensitivity to olaparib and carboplatin compared to BRCA1 wild-type cells. BRCA1 L1780P mutant TNBC cells showed decreased RAD51 expression and reduced nuclear RAD51 foci formation following carboplatin and olaparib treatment. The molecular interaction between p-ATM and BRCA1 was abrogated following introduction of BRCA1 L1780P mutant plasmid in TNBC cells, suggesting that the BRCA1 L1780P mutation disrupts the p-ATM-BRCA1 protein–protein interaction. We established an olaparib-resistant BRCA1 L1780P mutant TNBC cell line by chronic drug treatment. Olaparib-resistant cell lines showed upregulation of RAD51 expression upon olaparib treatment, and reduction in RAD51 expression in olaparib-resistant cells restored olaparib sensitivity. Collectively, these results suggest that the BRCA1 L1780P mutation impairs RAD51 recruitment by disrupting p-ATM-BRCA1 interaction, which is a crucial molecular factor in homologous recombination and olaparib sensitivity. Further therapeutic targeting of RAD51 in BRCA1 L1780P mutant breast cancer is warranted.

Triple-negative breast cancer (TNBC) is a severe and heterogeneous disease that lacks an approved targeted therapy and has a poor clinical outcome to chemotherapy. Although the RAS-ERK signaling axis is rarely mutated in TNBC, ~50% of TNBCs show an increased copy number and overexpression of epidermal growth factor receptor (EGFR). However, EGFR-targeted therapies have offered no improvement in patient survival, underscoring the need to explore downstream targets, including RAS. We found that both β-catenin and RAS, as well as epidermal growth factor receptor (EGFR), are overexpressed and correlated with one another in tumor tissues of TNBC patients. KYA1797K, an Axin-binding small molecule reducing β-catenin and RAS expression via degradation and suppressing EGFR expression via transcriptional repression, inhibited the proliferation and the metastatic capability of stable cell lines as well as patient-derived cells (PDCs) established from TNBC patient tissues. KYA1797K also suppressed the stemness of 3D-cultured PDCs and xenografted tumors established by using residual tumors from TNBC patients and those established by the TNBC cell line. Targeting both the Wnt/β-catenin and RAS-ERK pathways via small molecules simultaneously reducing the levels of β-catenin, RAS, and EGFR could be a potential therapeutic approach for TNBC., Breast cancer: Dual pathway blockade shrinks aggressive tumors The triple-negative breast cancer (TNBC), a highly aggressive form of breast cancer may be susceptible to drug therapy that targets two critical signaling pathways, one that governs cell fate and the other that controls the cell cycle. Researchers from Yonsei University in Seoul, South Korea, had previously synthesized a small-molecule called KYA1797K and found that could lower levels of the proteins, β-catenin (a master regulator of cell fate decisions) and RAS (which controls cell division), in colorectal cancer cells. Now, Kang-Yell Choi, Soonmyung Paik, and colleagues have shown that KYA1797K has the same effects on β-catenin and RAS levels in cells taken from patients with TNBC. In cell lines and mouse models, KY1797K suppressed the proliferation and metastatic capability of TNBC, highlighting the therapeutic potential of this strategy degrading both β-catenin and RAS.

Purpose Recent studies re-classified the c.5339T->C; p.Leu1780Pro (L1780P) BRCA1 missense mutation as “likely pathogenic” in ACMG classification, which shows high prevalence in Korean population. This study aims to reveal the molecular mechanisms and therapeutic relevance of BRCA1 L1780P mutation in DNA damaging response of triple-negative breast cancer (TNBC) cells. Method We established MDA-MB 231 and HCC1937 TNBC cell lines expressing BRCA1 wild-type and BRCA1 L1780P by stable transfection of plasmid DNAs. We performed cell proliferation assays of the TNBC cell lines with treatment of olaparib and carboplatin. We compared the protein and mRNA expression level of RAD51 in BRCA1 wild-type and L1780 transfected TNBC cell lines by western blot and RT-PCR, and BRCA1-mediated DNA damaging responses were evaluated by immunofluorescence staining of RAD51 upon olaparib and carboplatin treatment. The growth inhibitory potential of RAD51 inhibitor, RI-1 was tested in BRCA1 L1780P transfected TNBC cell lines. Results BRCA1 L1780P transfected TNBC cells showed higher migration and invasion capacity, as well as increased sensitivity to olaparib and carboplatin compared to BRCA1 wild-type transfected cells. The induction of RAD51 expression on carboplatin treatment was significantly decreased in BRCA1 L1780P TNBC cells compared with BRCA1 wild-type cells. BRCA1 L1780P transfected TNBC cells showed also showed reduced nuclear RAD51 foci formation on carboplatin and olaparib treatment. The molecular interaction between p-BRCA1 and ATM was decreased by BRCA1 L1780P introduction in TNBC cells, suggesting BRCA1 L1780P mutation disrupts binding of p-BRCA1-ATM. In a cell proliferation assay, BRCA1 L1780P transfected TNBC cells were highly sensitive to RAD51 inhibitor (IC50 = 4.15μM). Conclusion This study shows BRCA1 L1780P mutation causes defects in DNA damage responses of TNBC cells by disrupting molecular interaction between p-BRCA1 and ATM, resulting in RAD51 downregulation. The combinatory inhibition of RAD51 and PARP is a candidate strategy for TNBCs with BRCA1 L1780P mutation. Keywords: Triple-negative Breast Cancer; BRCA1 L1780 Mutation; Homologous Recombination Deficiency; RAD51 Citation Format: Jeong Dong Lee, Min Hwan Kim, Yeon A Choi, Won-Ji Ryu, Hyun Ju Han, Ae Ran Choi, Tae Yeong Kim, Joo Hyuk Sohn. Molecular characterization of BRCA1c.5339T>C missense mutation in DNA damage response of triple-negative breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2053.

1066 Background: Relevant predictive biomarkers for cyclin dependent kinase 4 and 6 (CDK4/6) inhibitors have not been identified in hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC). We investigated whether dynamic changes in the peripheral immune cells can predict therapeutic response to CDK4/6 inhibitors in ABC with translational relevance. Methods: Postmenopausal women who received palbociclib and letrozole for HR-positive, HER2-negative ABC from tertiary referral centers were analyzed (n = 221; exploratory cohort). Pre- and on-treatment leucocyte, neutrophil, lymphocytes counts, neutrophil-to-lymphocyte ratio (NLR), and derived NLR (dNLR; neutrophil/[leucocyte-neutrophil]) were correlated with survival outcomes. Patients from the PALOMA-2 study (NCT01740427) treated with letrozole with or without palbociclib (n = 410 and 209, respectively) were analyzed for validation (validation cohort). Prospectively enrolled patients were subjected to immunophenotyping with flow cytometry to explore the immune cell dynamics after CDK4/6 inhibitor treatment. Results: In the exploratory cohort, palbociclib administration significantly reduced leucocyte, neutrophil, and lymphocyte counts on cycle 2 day 1. Not baseline, but on-treatment neutrophil and lymphocyte counts were associated with superior and inferior outcomes, providing predictive significance to on-treatment NLR and dNLR for progression-free survival (PFS; HR = 1.64 and 2.52; all P< 0.001). In the validation cohort, higher on-treatment dNLR was associated with inferior PFS in patients treated with palbociclib and letrozole (HR = 1.50 and P= 0.009 with 1.04 cut-off), whereas not correlated with outcome in placebo and letrozole-administered patients. Exploratory analysis revealed that CDK4/6 inhibitor prevented T cell exhaustion and diminished relative frequencies of myeloid-derived suppressor cells, both of which trigger antitumor immunity. Conclusions: On-treatment dNLR significantly predicted treatment outcome in HR-positive, HER2-negative ABC treated with palbociclib and letrozole, allowing early prediction of treatment response with mechanistic insights. Clinical trial information: NCT01740427 .

Treatment of advanced gastric cancer patients with current standard chemotherapeutic agents frequently results in resistance, leading to poor overall survival. However, there has been no success in developing strategies to overcome it. We showed the expression levels of both &beta, catenin and RAS were significantly increased and correlated in tissues of 756 gastric cancer (GC) patients and tissues of primary- and acquired-resistance patient-derived xenograft tumors treated with 5-fluorouracil and oxaliplatin modulated with leucovorin (FOLFOX). On the basis of our previous studies, where small molecules to suppress colorectal cancer (CRC) via degrading both &beta, catenin and RAS were developed, we tested the effectiveness of KYA1797K, a representative compound functioning by binding axin, in the growth of GC cells. The efficacy test of the drugs using gastric tumor organoids of Apc1638N mice showed that the CD44 and ALDH1A3 cancer stem cell markers were induced by FOLFOX, but not by KYA1797K. KYA1797K also efficiently suppressed tumors generated by re-engrafting the FOLFOX-resistant patient-derived xenograft (PDX) tumors, which also showed resistance to paclitaxel. Overall, the small-molecule approach degrading both &beta, catenin and RAS has potential as a therapeutic strategy for treating GC patients resistant to current standard chemotherapies.