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Introduction: Cholangiocarcinomas (CCA) are rare, aggressive tumors often diagnosed in advanced stages with limited evidence guiding therapy on progression. Case Report: We report a case of advanced CCA with rapid and aberrant progression, refractory to multiple lines of therapy, that resulted in severe hepatic dysfunction secondary to tumor burden with a BRAF V600E mutation and high tumor proportion score (TPS) of 99%. To our knowledge, this is the first reported use of BRAF/MEK inhibition to target BRAF V600E in a patient with severe hepatic dysfunction leading to rapid normalization of the patient’s liver dysfunction within days. No adverse events were recorded during either initial titration or maintenance periods. Programmed death-1 (PD-1) inhibitor was added to BRAF/MEK inhibition, and the patient continues to have clinical therapeutic response. Conclusion: This case highlights the use of BRAF/MEK inhibition in CCA with BRAF V600E mutations in hepatic dysfunction due to tumor burden and the role of combining immune checkpoint inhibitors.

Introduction A high tumor mutational burden (TMB) (≥10 mut/Mb) has been associated with improved clinical benefit in non-small cell lung cancer (NSCLC) treated with immune checkpoint inhibitors (ICI) and is a tumor agnostic indication for pembrolizumab across tumor types. We explored whether combining TMB with programmed cell death ligand 1 (PD-L1) and pretreatment neutrophil-lymphocyte ratio (NLR) was associated with improved outcomes in ICI-treated NSCLC. Methods We retrospectively analyzed patients treated with ICI with Foundation One genomic testing, including TMB. Optimal cutoff for prediction of response by TMB was determined by receiver operating characteristic analysis, and area under the curve (AUC) was calculated for all 3 biomarkers and combinations. Cox model was used to assess prognostic factors of overall survival (OS) and time to progression (TTP). Survival cutoffs calculated with Kaplan-Meier survival curves were TMB ≥10 mut/Mb, PD-L1 ≥50%, NLR Results Data from 88 patients treated were analyzed. The optimal TMB cutoff was 9.24 mut/Mb (AUC, 0.62), improving to 0.74 combining all 3 biomarkers. Adjusted Cox model showed that TMB ≥10 mut/Mb was an independent factor of OS (hazard ratio [HR], 0.31; 95% confidence interval; 0.14-0.69; P = .004) and TTP (HR, 0.46; 95% CI, 0.27-0.77; P = .003). The combination of high TMB with positive PD-L1 and low NLR was significantly associated with OS (P = .038) but not TTP. Conclusions TMB has modest predictive and prognostic power for clinical outcomes after ICI treatment. The combination of TMB, PD-L1, and NLR status improves this power.

BACKGROUND: Bone metastases (BM) in renal cell carcinoma (RCC) patients are associated with poor outcomes. There are limited published data on outcomes in these patients with immunotherapy agents. We present a multi-institutional, retrospective analysis of metastatic RCC patients with BM treated with ipilimumab and nivolumab (I + N). OBJECTIVE: Patient, tumor, and treatment-related variables were retrospectively collected from electronic medical records of patients with a histologically confirmed diagnosis of RCC and at least one radiographically confirmed BM prior to initiation of I + N. Best objective response was assessed by clinical chart review, imaging reports, and treating physician evaluation; progression-free survival (PFS) and overall survival (OS) were recorded as of 31 December 2020. Descriptive statistics were used to summarize patient characteristics and BM-related variables. Kaplan-Meier method and Mantel-Haenszel log-rank test were used to compare survival among groups. Cox regression univariable and multivariable models were used to correlate patient- and treatment-related variables to outcomes. RESULTS: Eighty patients with RCC and BM treated with I + N were identified. Patients were predominantly male and Caucasian presenting primarily with IMDC intermediate or poor-risk clear-cell RCC. Best response to I + N was progressive disease (46%), stable disease (28%), partial response (21%), and not evaluable (5%). Median PFS was 6.1 months (95% CI 3.8–8.9 months) with the majority of patients (65%) discontinuing I + N due to disease progression. Median OS was 25.6 months (95% CI 14.9–NA) with median follow-up of 25.2 months. A multivariable regression model for PFS showed several variables to be significantly associated with worse PFS including female gender [p = 0.02; hazard ratio (HR) 2.16; 95% CI 1.14–4.12], metastases to other sites (p = 0.006; HR 2.12; 95% CI 1.24–3.62) and presence of BM to ribs (p = 0.0007; HR 2.61; 95% CI 1.50–4.52). A multivariable Cox model of OS showed no prior radiation therapy to BM (p = 0.02; HR 2.17; 95% CI 1.13–4.17) and presence of liver metastases (p = 0.0006; HR 3.19; 95% CI 1.65–6.19) to be significantly associated with worse OS. CONCLUSION: RCC patients with ≥ 1 BM who received I + N therapy had a relatively low response rate, PFS, and OS. Strategies to improve outcomes in this subset of patients are needed.

BackgroundImmunotherapy combinations including ipilimumab and nivolumab are now the standard of care for untreated metastatic renal cell carcinoma (mRCC). Biomarkers of response are lacking to predict patients who will have a favorable or unfavorable response to immunotherapy. This study aimed to use the OmniSeq transcriptome-based platform to develop biomarkers of response to immunotherapy.MethodsTwo cohorts of patients were retrospectively collected. These included an investigational cohort of patients with mRCC treated with immune checkpoint inhibitor therapy from five institutions, and a subsequent validation cohort of patients with mRCC treated with combination ipilimumab and nivolumab from two institutions (Duke Cancer Institute and Cleveland Clinic Taussig Cancer Center). Tissue-based RNA sequencing was performed using the OmniSeq Immune Report Card on banked specimens to identify gene signatures and immune checkpoints associated with differential clinical outcomes. A 5-gene expression panel was developed based on the investigational cohort and was subsequently evaluated in the validation cohort. Clinical outcomes including progression-free survival (PFS) and overall survival (OS) were extracted by retrospective chart review. Objective response rate (ORR) was assessed by Response Evaluation Criteria in Solid Tumors (RECIST) V.1.1.ResultsThe initial investigation cohort identified 86 patients with mRCC who received nivolumab (80%, 69/86), ipilimumab/nivolumab (14%, 12/86), or pembrolizumab (6%, 5/86). A gene expression score was created using the top five genes found in responders versus non-responders (FOXP3, CCR4, KLRK1, ITK, TIGIT). The ORR in patients with high gene expression (GEhigh) on the 5-gene panel was 29% (14/48), compared with low gene expression (GElow) 3% (1/38, χ2p=0.001). The validation cohort was comprised of 62 patients who received ipilimumab/nivolumab. There was no difference between GEhighand GElowin terms of ORR (44% vs 38.5%), PFS (HR 1.5, 95% CI 0.58 to 3.89), or OS (HR 0.96, 95% CI 0.51 to 1.83). Similarly, no differences in ORR, PFS or OS were observed when patients were stratified by tumor mutational burden (high=top 20%), PD-L1 (programmed death-ligand 1) expression by immunohistochemistry or RNA expression, or CTLA-4 (cytotoxic T-lymphocytes-associated protein 4) RNA expression. The International Metastatic RCC Database Consortium (IMDC) risk score was prognostic for OS but not PFS.ConclusionA 5-gene panel that was associated with improved ORR in a predominantly nivolumab monotherapy population of patients with mRCC was not predictive for radiographic response, PFS, or OS among patients with mRCC treated with ipilimumab and nivolumab.

Background The identification of biomarkers to select patients with metastatic renal cell carcinoma (mRCC) most likely to respond to combination immunotherapy (IO) is needed. We sought to investigate an association of the baseline neutrophil-to-eosinophil ratio (NER) with outcomes to nivolumab plus ipilimumab for patients with mRCC. Methods We performed a retrospective review of patients with clear cell mRCC treated with nivolumab plus ipilimumab from Vanderbilt-Ingram Cancer Center and Duke Cancer Institute. Patients with prior receipt of immunotherapy and those without available baseline complete blood count with differential were excluded. Patients were divided into groups by the median baseline NER and analyzed for overall survival (OS), progression free survival (PFS), and objective response rate (ORR). Patients were also divided by median baseline neutrophil-to-lymphocyte ratio (NLR) and analyzed for clinical outcome. Further analyses of patients above/below the median NER and NLR were performed in subgroups of IMDC intermediate/poor risk, IMDC favorable risk, and treatment naïve patients. Results A total of 110 patients were included: median age was 61 years and 75% were treatment naïve. The median NER (mNER) at baseline was 26.4. The ORR was 40% for patients with mNER (OR 2.39, p = 0.04). The median PFS for patients with mNER (HR 0.50, p mNER (HR 0.31, p p = 0.02), PFS and ORR did not differ compared with patients in the >mNLR group. Conclusions A lower baseline NER was associated with improved clinical outcomes (PFS, OS, and ORR) in patients with mRCC treated with nivolumab plus ipilimumab, and prospective validation of the baseline NER as a predictive biomarker for response to immunotherapy-based combinations in mRCC is warranted.

The combination of ipilimumab plus nivolumab (I+N) has greatly improved outcomes in patients with intermediate or poor-risk untreated metastatic renal cell carcinoma (mRCC). However, little is known about the outcomes of patients with brain metastasis (BrM) treated with I+N. A search was performed to retrospectively identify all patients with mRCC treated with I+N in the Duke Cancer Institute and the Cleveland Clinic Taussig Cancer Center, followed by a chart review. Patients were included if they had BrM at the time of I+N initiation. Cohort characteristics are summarized with descriptive statistics. Kaplan-Meier method was used to estimate overall survival (OS) and global, intracranial, and extracranial progression-free survival (PFS) for the cohort and log rank test was used to compare OS and PFS between patient groups. Radiographic response was categorized by RECIST. Fisher’s exact test was used to correlate patient factors with radiographic response. From October 2017 to December 2020, 19 patients with BrM received I+N for mRCC with a median follow-up time of 27.1 months (range 15.0–35.6). By International Metastatic RCC Database Consortium (IMDC) risk criteria, 16% had favorable, 58% had intermediate, and 26% had poor-risk disease. 68% were systemic therapy naïve, and 77% of patients had clear cell histology. 95% had received local CNS directed therapy with surgery, radiotherapy, or both. The objective response rate was 44% (0% complete response) with three of six patients treated in the second line or greater setting experiencing a partial response. The median PFS was 7.6 months (95% CI 5.6 to 14.9). The median extracranial PFS was 8.5 months (95% CI 5.6 to 19.7), and median intracranial PFS was 14.7 months (95% CI 7.2 to not reached). No variables assessed were significantly associated with radiographic response (gender, IMDC risk, presence of bone metastasis, line of therapy, or presence of immune related adverse events). In our retrospective cohort of patients with mRCC with BrM, I+N, in combination with CNS-directed local therapy, appears to have clinical efficacy as previously described with responses seen beyond the first-line setting. Further investigation is warranted in this population given exclusion from prior clinical trials.

Highlights • COVID-19 patients are at increased risk of thromboembolic complications. • Escalated-dose thromboprophylaxis may help reduce the rate of thromboembolic events. • The bleeding risk is highest for patients treated with therapeutic anticoagulation.

BackgroundLow-density lipoprotein receptor-related protein 1b (encoded by LRP1B) is a putative tumor suppressor, and preliminary evidence suggests LRP1B-mutated cancers may have improved outcomes with immune checkpoint inhibitors (ICI).MethodsWe conducted a multicenter, retrospective pan-cancer analysis of patients with LRP1B alterations treated with ICI at Duke University, Johns Hopkins University (JHU) and University of Michigan (UM). The primary objective was to assess the association between overall response rate (ORR) to ICI and pathogenic or likely pathogenic (P/LP) LRP1B alterations compared with LRP1B variants of unknown significance (VUS). Secondary outcomes were the associations with progression-free survival (PFS) and overall survival (OS) by LRP1B status.ResultsWe identified 101 patients (44 Duke, 35 JHU, 22 UM) with LRP1B alterations who were treated with ICI. The most common tumor types by alteration (P/LP vs VUS%) were lung (36% vs 49%), prostate (9% vs 7%), sarcoma (5% vs 7%), melanoma (9% vs 0%) and breast cancer (3% vs 7%). The ORR for patients with LRP1B P/LP versus VUS alterations was 54% and 13%, respectively (OR 7.5, 95% CI 2.9 to 22.3, p=0.0009). P/LP LRP1B alterations were associated with longer PFS (HR 0.42, 95% CI 0.26 to 0.68, p=0.0003) and OS (HR 0.62, 95% CI 0.39 to 1.01, p=0.053). These results remained consistent when excluding patients harboring microsatellite instability (MSI) and controlling for tumor mutational burden (TMB).ConclusionsThis multicenter study shows significantly better outcomes with ICI therapy in patients harboring P/LP versus VUS LRP1B alterations, independently of TMB/MSI status. Further mechanistic and prospective validation studies are warranted.

Introduction Two separate antiangiogenic tyrosine kinase inhibitors (TKIs) and immunotherapy (IO) combinations are FDA‐approved as front‐line treatment for metastatic renal cell carcinoma (mRCC). Little is known about off‐protocol and post‐front‐line experience with combination TKI–IO approaches. Methods We conducted a retrospective analysis of mRCC patients who received combination TKI–IO post‐first‐line therapy between November 2015 and January 2019 at MD Anderson Cancer Center and Duke Cancer Institute. Chart review detailed patient characteristics, treatments, toxicity, and survival. Independent radiologists, blinded to clinical data, assessed best radiographic response using RECIST v1.1. Results We identified 48 mRCC patients for inclusion: median age 65 years, 75.0% clear cell histology, 68.8% IMDC intermediate risk, and median two prior systemic therapies. TKI–IO combinations included nivolumab–cabozantinib (N +C; 24 patients), nivolumab–pazopanib (N+P; 13), nivolumab–axitinib (6), nivolumab–lenvatinib (2), and nivolumab–ipilimumab–cabozantinib (3). The median progression‐free survival was 11.6 months and the median overall survival was not reached. Response data were available in 45 patients: complete response (CR; n = 3, 6.7%), partial response (PR; 20, 44.4%), stable disease (SD; 19, 42.2%), and progressive disease (3, 6.7%). Overall response rate was 51% and disease control rate (CR+PR+SD) was 93%. Only one patient had a grade ≥3 adverse event. Conclusion To our knowledge, this is the first case series reporting off‐label use of combination TKI–IO for mRCC. TKI–IO combinations, particularly N+P and N+C, are well tolerated and efficacious. Although further prospective research is essential, slow disease progression on IO or TKI monotherapy may be safely controlled with addition of either TKI or IO., Real world use of combination anti‐angiogenic tyrosine kinase inhibitor (TKI)—anti‐PD1 immunotherapy (IO) is feasible, well tolerated and efficacious for metastatic renal cell carcinoma in the second line setting and beyond. Although further prospective research is essential to define optimal use of salvage TKI‐IO, slow disease progression on IO or TKI monotherapy may be safely controlled with addition of either a TKI or IO.

We report a case using combination cabozantinib/nivolumab to salvage disease control in a patient with refractory metastatic renal cell carcinoma (mRCC). The patient had previously experienced disease progression from high dose IL-2, sunitinib, pazopanib, cabozantinib, and nivolumab, all given sequentially. Combination cabozantinib/nivolumab resulted in 22 months of disease control. Vascular endothelial growth factor (VEGF) inhibitors including cabozantinib have immunomodulatory effects when combined with immune checkpoint inhibitors, with multiple ongoing phase 3 trials exploring the cabozantinib/nivolumab combination in the first line setting. To our knowledge, this is the first reported case of progression on nivolumab and cabozantinib when given as sequential monotherapies but stable disease on combination cabozantinib/nivolumab. IMPLICATIONS FOR PRACTICE: There is ongoing evaluation of combination VEGF-targeted therapies and immune checkpoint inhibitors given their potential mechanistic synergy. With the recent CHECKMATE 9ER press release reporting clinically meaningful benefit from the combination cabozantinib/nivolumab compared to sunitinib in the first line setting, this case of sustained stable disease with combination cabozantinib/nivolumab after progression on prior VEGF-targeting therapies and immunotherapies highlights the activity of this combination as a potential treatment alternative to improve disease control.

Introduction: Early studies identified a prothrombotic state associated with novel coronavirus disease 2019 (COVID-19) as well as a survival benefit observed with heparin use in severely ill COVID-19 patients. There is a need to clarify the incidence of thromboembolic events (TEs), as well as major hemorrhage in COVID-19 patients in the context of an escalated-dose thromboprophylaxis strategy. Methods: We conducted a single center, retrospective study of 192 consecutive patients with COVID-19 admitted to the hospital between March 26th and May 8th 2020. Our study aimed to investigate the rates of thromboembolic events (TEs), hemorrhage and mortality of in the context of an escalated-dose thromboprophylaxis strategy implemented early in our experience with hospitalized patients with COVID-19. Results: The incidence of radiographically-confirmed venous thromboembolism (VTE) was 7.3% (n=14), and the rate of combined TEs was 12% (n=23). The rate of major hemorrhage was 6.3% (n=12), including one fatal CNS bleed. The overall mortality rate was 27.6% (n=53). Conclusion: The rate of VTE and overall TE was much lower than was reported in early studies, and the majority of VTEs occurred in ambulatory patients. Our data suggest that an escalated-dose thromboprophylaxis strategy may help reduce the incidence of inpatient VTEs, and that ambulatory COVID-19 patients may benefit from primary thromboprophylaxis. However, the risk of bleeding was not negligible, and must therefore be assessed on an individual and continual basis when using a more aggressive thromboprophylaxis strategy. Disclosures No relevant conflicts of interest to declare.

4563 Background: Previous reports have shown that the baseline neutrophil-to-lymphocyte ratio (NLR) is associated with prognosis in patients with mRCC. However, NLR has not been shown to reliably predict for response to IO. Retrospective analyses in metastatic melanoma and mRCC have shown an association of eosinophilia with improved outcomes to single agent immunotherapy. We sought to evaluate and compare the baseline NLR and NER with response to ipi/nivo in patients with mRCC. Methods: A retrospective review of patients with mRCC treated at the Vanderbilt-Ingram Cancer Center or Duke Cancer Institute with ipi/nivo was performed. Patients with clear cell histology and a baseline complete blood count with differential were included. Patients previously treated with IO were excluded. Patients were separated into groups (above and below the median) based on baseline median NER and baseline median NLR. Analyses of progression free survival (PFS) and overall survival (OS) were conducted using the log rank test. The odds ratio (OR) for objective response rate (ORR) was analyzed using Fisher’s exact test. Results: 111 patients met inclusion criteria. The median age was 60, 77% of patients were male, 68% had prior nephrectomy, 74% were naïve to systemic therapy, and 84% were IMDC intermediate/poor risk. The median NER was 25.0 and median NLR was 3.4. Patients with < median baseline NER had significant improvement in PFS, OS, and ORR (see table). Patients with < median baseline NLR had significant improvement in OS but not in PFS or ORR. Conclusions: Baseline NER was associated with improved outcomes with ipi/nivo. While both NER and NLR were associated with improved OS, only NER was additionally associated with both improved PFS and ORR. With multiple first-line treatment options for mRCC, baseline NER may serve as an early non-invasive predictor for response to ipi/nivo.[Table: see text]

10586 Background: Clonal hematopoiesis (CH) is the presence of expanded somatic clones in hematopoietic cells and is associated with higher overall mortality (OM). Studies suggest atherosclerotic cardiovascular disease may drive mortality, but the detailed mechanisms remain unclear. CH mutations can be detected in solid tumor sequencing, often confounding genomic tumor analysis. We evaluated the association of CH in solid tumor next-generation sequencing (NGS) with echocardiographic findings and OM. Methods: Sequential adult patients treated at the Duke Cancer Institute with solid tumor NGS analysis by FoundationOne were captured retrospectively. CH mutations present at a variant allele fraction ≥2% across 57 genes previously associated with hematologic malignancies were included. Patients with echocardiograms between 2 years before NGS testing and up to 5 years afterward were analyzed. Association between CH mutations with cardiomyopathy (CM, left ventricular ejection fraction < 45%) and global longitudinal strain (GLS) was determined using logistic and linear regression, respectively. In a subset of patients with detailed cancer diagnosis date and clinical follow-up, Cox proportional hazard models were used to associate CH mutations with OM, with or without TP53/ KRAS (included in most CH analyses but highly prevalent in solid tumors). Analyses were adjusted for age, gender and race. Results: Of 3029 patients with NGS testing, 2212 (73.0%) carried at least one CH related mutation, the majority of which were in TP53/ KRAS. When excluding TP53/ KRAS, CH mutations were observed in 806 of 3029 (26.6%) patients. CH mutations were associated with age (est 2.1, 95% CI 1.1-3.2, p < 0.001). Excluding TP53/ KRAS strengthened the association between CH and age (est 2.8, 95% CI 1.8-3.9, p < 0.001). Echocardiogram data were available in 828 patients, of whom 48 (5.8%) had CM. CH mutations were not associated with CM (OR 1.3, 95% CI 0.6-2.6, p = 0.5), however when excluding TP53 and KRAS, CH mutations were associated with lower odds of (OR 0.4, 95% CI 0.1-0.9, p = 0.03). GLS was available in 423 patients and was not associated with CH mutations (p = 0.8 with TP53/ KRAS; p = 0.4 without TP53/ KRAS as CH). In 222 patients with clinical information, OM did not differ between the CH vs no CH cohorts (HR 0.8, 95% CI 0.6 = 1.2, p = 0.3 inclusive of TP53/KRAS). When excluding TP53/ KRAS mutations, in this population of patients with cancer, non- TP53/ KRAS CH was associated with less OM (HR 0.6, 95% CI 0.4-0.9, p = 0.01). Conclusions: In this patient population with cancer, CH mutations did not associate with higher CM. In contrast to prior studies, CH detected in solid tumor does not associate with OM in this population. CH mutations confound tumor sequencing and these findings support the value of paired tumor-blood sequencing to determine true CH. Consensus around CH variants should be undertaken in future studies.

e17090 Background: Two immunotherapy (IO) and tyrosine kinase inhibitor (TKI) combinations are FDA-approved for patients (pts) with metastatic renal cell carcinoma (mRCC). Here we present a multicenter off-protocol experience with IO/TKI combinations after progression on monotherapy. Methods: We performed a retrospective analysis of pts with mRCC who received combination non-FDA approved off-protocol IO/TKI combination therapy from 11/2015 – 1/2019 at MD Anderson Cancer Center and Duke Cancer Institute. Results: 48 pts met criteria for study inclusion. At therapy start: median (med) age 65 years; 75% clear cell histology; 68.8% IMDC intermediate risk (20.8% favorable, 10.4% poor); 81.3% prior nephrectomy; med metastatic sites: 2; med prior systemic treatments: 2; most common metastatic sites: lung (58.3%), lymph node (52.1%), and bone (43.8%). Pts received nivolumab (nivo) in combination with the following: cabozantinib (n = 24, 50%), pazopanib (13, 27.1%), axitinib (6, 12.5%), lenvatinib (2, 4.2%), ipilimumab/cabozantinib (3, 6.3%). Med PFS was 13.7 months and med OS was not reached. The two largest cohorts received nivo + cabozantinib (N+C; med dose 40 mg daily) or nivo + pazopanib (N+P; med dose 400 mg daily). The N+C cohort had higher med metastatic sites (3 vs 2) and was more pretreated with agents unique to their IO/TKI combination (med 2 vs 0). In the N+P group, more pts had started on TKI prior to addition of nivo at progression (69.2% vs 45.8%), and fewer had IO monotherapy with TKI addition (30.8% vs 50%). With a med follow up of 14.0 months after combination start, the N+C cohort had a med PFS of 7.3 months (initiated TKI first: 4.8, IO first: 8.2) and med OS of 18.2 months (TKI first: 11.8, IO first: 24.3). The N+P cohort had med follow up of 20.5 months after combination, med PFS of 21.3 months (TKI first: 16.5, IO first: 21.8), and med OS was not reached. In the N+C group, 87.5% experienced any grade adverse event (AE), most common included fatigue (79.2%), diarrhea (42.7%), nausea (29.2%), hypertension (29.2%), and weight loss (25.0%). In the N+P group, 92.3% experienced any grade AE, including fatigue (76.9%), hypertension (38.5%), diarrhea (30.8%), nausea (30.8%), and weight loss (30.8%). There were no grade ≥3 AEs. Conclusions: Slow disease progression on nivo or TKI may be safely controlled with addition of IO/TKI therapy. Med PFS after addition of nivo to TKI appears similar (N+C) and improved (N+P) compared to nivo monotherapy (Checkmate-025). Med PFS after addition of TKI to IO was also similar (N+C) and improved (N+P) compared to historical controls.

3007 Background: Low-density lipoprotein receptor-related protein 1b (LRP1b) is a putative tumor suppressor and one of the most frequently altered genes in cancer. Our prior single-center work suggested that LRP1B alterations may enrich for responses to immune checkpoint inhibitors (ICI) in solid tumors including prostate cancer; however, validation of these findings is needed. Methods: We conducted a multicenter, retrospective analysis of patients with LRP1B alterations (on tissue-based next-generation sequencing panels) treated with ICI at Duke, Johns Hopkins (JHU), and University of Michigan (UM). The primary objective was to assess the association between objective response rate (ORR) to ICI and pathogenic LRP1B alterations, defined as deletions or truncating alterations, when compared with LRP1B variants of undetermined significance (VUS), defined as missense mutations not predicted to be pathogenic in COSMIC. Missense changes with a COSCMIC FATHMM score of > 0.8 were categorized separately as likely pathogenic. Summary statistics, ORR, progression free survival (PFS), and overall survival (OS) were calculated. Results: 101 patients (44 Duke, 35 JHU, 22 UM) with LRP1B alterations were treated with ICI. Median age was 61 (range 32-82). The most common tumor types by alteration (pathogenic or likely pathogenic/VUS%) were lung (33/47%), GI (17/13%), prostate (11/7%), sarcoma (2/9%), melanoma (11/0%), and others (26/24%). 93% of patients received single-agent PD-(L)1 inhibition. The ORR for patients with either pathogenic/likely pathogenic alterations, or VUS alterations was 57% and 18%, respectively. After excluding MSI-high or TMB-high ( > 10 mut/Mb) tumors, ORR was 14/25 (56%) and 6/36 (17%), respectively. Pathogenic or likely pathogenic LRP1B alterations were associated with longer PFS (HR 0.39, 95% CI 0.24-0.63) and OS (HR 0.58, 95% CI 0.36-0.95). Conclusions: This multicenter study shows impressive and durable objective response rates to ICI for patients harboring pathogenic LRP1B alterations when compared to those with LRP1B VUS, independent of TMB/MSI status. Further mechanistic insights and prospective validation studies are warranted. [Table: see text]

648 Background: Ipilimumab & nivolumab (I+N) followed by nivolumab maintenance is approved as front-line therapy for intermediate and poor-risk metastatic renal cell carcinoma (mRCC). Bone metastases (BM) are present in up to 30% of mRCC patients (pts) and remain a clinical challenge. We present a multicenter experience of mRCC pts with BMs treated with I+N. Methods: Patients with mRCC and bone metastases treated with (I+N) at Duke Cancer Network and Cleveland Clinic were retrospectively reviewed. Patient demographics, tumor histology, IMDC risk stratification, RECIST-defined ORR and adverse events were collected. Fisher’s exact test was used to determine predictors of response (alpha 0.05). Results: Forty-eight pts with mRCC and radiographically confirmed BMs were included in the analysis: 81% male; median age 54 (range: 41-81); 77% clear cell histology; IMDC risk 17%/52%/31% favorable/intermediate/poor, respectively. I+N was used as first-line medical therapy in 63% of pts and ≥ second-line in remaining pts. Best response on I+N per RECIST criteria: objective response rate (ORR) 23% (0% CR); 23% stable disease (SD); 44% progressive disease (PD). Median duration of treatment was 64 days with 27% of pts still on I+N. PD was the most common reason for discontinuation (38%) followed by adverse events (19%). Nearly half of pts (48%) experienced at least one irAE attributed to I+N therapy. None of the factors examined above was significantly associated with response to treatment. Conclusions: I+N has clinical activity and is well tolerated in mRCC pts with bone metastases; however ORR in this population is lower than expected and 44% pts had PD as best response. Therefore, identifying prognostic factors & improving novel therapies for this cohort of patients are priorities, given overall poorer outcomes in this population.

637 Background: The combination of ipilimumab & nivolumab (I+N) followed by maintenance nivolumab has improved outcomes in patients (pts) with mRCC. Little is known about the outcomes in mRCC pts with brain metastasis. In this multicenter retrospective analysis, we present a real-world experience in pts with brain metastasis treated with I+N. Methods: Pts with mRCC and brain metastases treated with I+N at the Duke Cancer Institute and Cleveland Clinic were identified. Pt characteristics were summarized with descriptive statistics. Fisher’s exact test was used to determine predictors of response (alpha 0.05). Results: From 10/2017 to 2/2019, 17 pts received I+N for mRCC with brain metastases. Median age was 60; 29% were female. IMDC risk was 18%/59%/24% favorable/intermediate/poor, and 77% were clear cell histology. Pts received I+N as either first-line (65%) or ≥ second-line (35%) therapy. Of the pts evaluable for response: objective response rate (ORR) was 42% [0% CR]; with 29% achieving stable disease and 18% progressive disease as their best response. Median duration on therapy was 13 weeks. 59% of pts developed an immune-related adverse event (AE). The most common reason for treatment discontinuation was disease progression (47%) followed by AEs (18%). There were no significant predictors of any radiographic response category (PR, SD, or PD) among variables assessed (gender, IMDC risk, histology, presence of bone metastasis, line of therapy, or presence of irAE). Of note, 50% (3/6) patients treated in the second-line or greater setting experienced a PR. Conclusions: In our real-world cohort of mRCC patients with brain metastasis, I+N is clinically effective. Further investigation is warranted in this population given exclusion from prior clinical trials.

80 Background: TMB is a promising predictive biomarker for ICB, but recent studies have shown that TMB varies substantially between tumor types. We examined the association between TMB and clinical response to ICB in metastatic urothelial carcinoma (mUC), renal cell carcinoma (mRCC), and non-small cell lung cancer (mNSCLC). Methods: We conducted a single center retrospective study inclusive of 1444 consecutive patients (pts) initiating ICB prior to 1/2019, cross-referenced with pts with Foundation One testing with TMB (mut/Mb), resulting in 17 mUC, 10 mRCC, and 60 mNSCLC. PD-L1 status was determined by the Dako 22C3 antibody. Pts were divided into clinical responders (R) and non-responders (NR) based on clinical assessment per their oncologist. The primary outcome of the study was to describe the relationship between TMB and clinical benefit, including duration of clinical response and overall survival (OS). A t-test was performed between R groups. Kaplan Meier (KM) curves and Cox-Mantel log rank tests were performed for PFS/OS comparing high TMB (≥ median) to low TMB pts. Results: For mUC, 8/17 (47%) were R with median TMB 7.74 (Interquartile range or IQR 6.04-9.78) compared to 9 NR, median TMB 7.57 (IQR 3.78-11.41) [p = 0.36]. For mRCC, 4/10 (40%) were R with median TMB 1.75 (IQR 1.75-1.97), versus 6 NR with median TMB 5.79 (IQR 3.07-7.48) [p = 0.02]. For mNSCLC, 30/60 (50%) were R with median TMB 11.38 (IQR 9.65-16.24), significantly higher than 30 NR with median TMB 9.46 (IQR 7.65-13.87) [p = 0.05]. For mNSCLC, no difference in PD-L1 positivity was found between R (17/30, 56%) and NR (16/30, 53%), and concurrent chemotherapy with ICB was the same in both R (10/30 (33%)) and NR (10/30 (33%)). KM analysis showed equivocal results for duration of clinical response and OS between high TMB vs low TMB in the three solid tumors, except OS in mUC which favored high TMB (p = 0.03) [cutoff TMB: mUC 7.57, mRCC 2.63, mNSCLC 11.35]. Conclusions: Higher TMB was associated with a greater likelihood of clinical benefit to ICB in our cohort of NSCLC patients and mUC. This correlation was not detected among mRCC patients, although these data are limited by relatively small number of cases.

e14291 Background: Low-density lipoprotein receptor-related protein 1B (LRP1B) is a putative tumor suppressor gene spanning > 500 kb on chromosome 2. A melanoma study previously reported enrichment of LRP1B mutations in responders (34%) to immune checkpoint inhibitors (ICIs) compared with non-responders (3%). Deep deletions in LRP1B are frequently observed in non-small cell lung cancer (NSCLC, 12%), head and neck (11%), cervical (9%), bladder (8%), and prostate cancers (8%). This study examines the clinical response to ICIs in a diverse group of tumor types with LRP1B alterations. Methods: We conducted a single center retrospective study inclusive of all patients (pts) with tumors containing any LRP1B variant who were treated with an ICI between 01/2015 and 11/2018. The primary outcome of the study was to describe the clinical outcomes of patients with LRP1B alterations, with respect to radiographic response to therapy, time on therapy, duration of response, and overall survival. Results: 44 pts with an LRP1B variant were treated with an ICI at Duke between 01/2015 and 11/2018. The most common ICIs were pembrolizumab (29/44, 66%) and nivolumab (12/44, 27%). Tumor types included NSCLC (24/44, 55%), renal cell carcinoma (RCC, 5/44, 11%), and prostate cancer (5/44, 11%). 14 (32%) pts had pathogenic variants (PVs) and 30 pts (68%) had variants of uncertain significance (VUS). Among pts with LRP1b PVs, 36% (95%CI 14%-64%) had radiographic responses (5/14, 2 lung, 1 prostate, 1 RCC, 1 endometrial carcinoma), two of whom were MSI high. As a control, the radiographic response rate among patients with a LRP1b VUS was 10% (95%CI 3%-28%). Of those with PVs, 3 pts had stable disease, one of whom has been on CPI therapy for > 22 months and 5 (36%) remain on therapy, with 2 (14%) pts discontinued due to immune toxicities, and 7 (50%) pts discontinued due to disease progression. The median TMB among responders was 12 (2-150.05 mut/Mb) and the median TMB amongst non-responders was 9.5 (6-18 mut/Mb). Conclusions: In a tumor agnostic population of pts harboring LRP1B PVs, 36% of pts have responses to ICI. The majority of responders were MSS and TMB low, which may suggest that PV in LRP1B may independently predict for response to ICI. Prospective and multicenter validation is now needed.