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The 2022 Coffey-Holden Prostate Cancer Academy (CHPCA) Meeting, "Exploring New Frontiers in Prostate Cancer Research," was held from June 23 to 26, 2022, at the University of California, Los Angeles, Luskin Conference Center, in Los Angeles, CA.The CHPCA Meeting is an annual discussion-oriented scientific conference organized by the Prostate Cancer Foundation, that focuses on emerging and next-step topics deemed critical for making the next major advances in prostate cancer research and clinical care. The 2022 CHPCA Meeting included 35 talks over 10 sessions and was attended by 73 academic investigators.Major topic areas discussed at the meeting included: prostate cancer diversity and disparities, the impact of social determinants on research and patient outcomes, leveraging real-world and retrospective data, development of artificial intelligence biomarkers, androgen receptor (AR) signaling biology and new strategies for targeting AR, features of homologous recombination deficient prostate cancer, and future directions in immunotherapy and nuclear theranostics.This article summarizes the scientific presentations from the 2022 CHPCA Meeting, with the goal that dissemination of this knowledge will contribute to furthering global prostate cancer research efforts.

Granulocytic–macrophage colony-stimulating factor (GM-CSF) is used as an adjuvant in cancer vaccine trials and has the potential to enhance antitumor efficacy with immunotherapy; however, its immunologic effects are not fully understood. Here, we report results from a phase I study of neoadjuvant GM-CSF in patients with localized prostate cancer undergoing radical prostatectomy. Patients received subcutaneous injections of GM-CSF (250 μg/m2/day) daily for 2 weeks (cohort 1; n = 6), 3 weeks (cohort 2; n = 6), or 4 weeks (cohort 3; n = 6). Treatment was well tolerated with all grade 1 or 2 adverse events. Two patients had a decline in prostate-specific antigen (PSA) of more than 50%. GM-CSF treatment increased the numbers of circulating mature myeloid dendritic cells, proliferating conventional CD4 T cells, proliferating CD8 T cells, and to a lesser magnitude FoxP3+ regulatory CD4 T cells. Although GM-CSF treatment did not augment antigen-presenting cell localization to the prostate, treatment was associated with recruitment of CD8+ T cells to the tumor. These results suggest that systemic GM-CSF can modulate T-cell infiltration in the tumor microenvironment. Cancer Immunol Res; 4(11); 948–58. ©2016 AACR.

Programmed death 1 (PD-1) and PD ligand 1 (PD-L1) inhibitors have shown activity in metastatic clear cell renal cell carcinoma (ccRCC). Data on the activity of these agents in patients with non–clear cell RCC (nccRCC) or patients with sarcomatoid/rhabdoid differentiation are limited. In this multicenter analysis, we explored the efficacy of PD-1/PD-L1 inhibitors in patients with nccRCC or sarcomatoid/rhabdoid differentiation. Baseline and follow-up demographic, clinical, treatment, and radiographic data were collected. The primary endpoint was objective response rate. Secondary endpoints include time-to-treatment failure (TTF), overall survival (OS), and biomarker correlates. Forty-three patients were included: papillary (n = 14; 33%), chromophobe (n = 10; 23%), unclassified (n = 9; 21%), translocation (n = 3; 7%), and ccRCC with sarcomatoid differentiation (n = 7, 16%). Of those 43 patients, 11 patients (26%) had sarcomatoid and/or rhabdoid differentiation (n = 7 with ccRCC; n = 4 nccRCC). Overall, 8 patients (19%) objectively responded, including 4 patients (13%) who received PD-1/PD-L1 monotherapy. Responses were observed in patients with ccRCC with sarcomatoid and/or rhabdoid differentiation (n = 3/7, 43%), translocation RCC (n = 1/3, 33%), and papillary RCC (n = 4/14, 29%). The median TTF was 4.0 months [95% confidence interval (CI), 2.8–5.5] and median OS was 12.9 months (95% CI, 7.4–not reached). No specific genomic alteration was associated with clinical benefit. Modest antitumor activity for PD-1/PD-L1–blocking agents was observed in some patients with nccRCC. Further prospective studies are warranted to investigate the efficacy of PD-1/PD-L1 blockade in this heterogeneous patient population. Cancer Immunol Res; 6(7); 758–65. ©2018 AACR.

Includes: Table 1S. Baseline patient and disease characteristics. Table 2S. Tumor mutation burden status. Table 3S. PDL1 expression data. Figure 1S. Overall survival for the total cohort.

1. Supplementary table 1S describing details of biopsies undergoing WES. 2. Table 2S includes the primers used in the CTC gene expression analysis. 3. Table 3S includes summary of PSA response based on prior treatment. 4. Table 4S includes objective response in the overall cohort and based on patients with measurable and non-measurable disease. 5. Table 5S is the PSA progression and radiographic PFS based on prior lines of treatment. 6. Table 6S is the adverse events in >10% of patients. 7. Table 7S is a listing of the biopsy procedures and outcomes. 8. Table 8S is the frequency of genomic alterations in the baseline and progression samples and PSA response data. 9. Table 9S includes the details for the AR mutations observed in the baseline and progression samples. 10. Figure 1S includes the KM curves for PSA progression and radiographic PFS. 11. Figure 2S includes the Consort Diagram for the study. 12. Figure 3S includes the integrative data of paired biopsy and CTC samples. 13. Figure 4S includes the KM curves for time to PSA progression, radiographic PFS, and overall survival in the CTC biomarker groups.

Purpose:Enzalutamide is a second-generation androgen receptor (AR) inhibitor that has improved overall survival (OS) in metastatic castration-resistant prostate cancer (CRPC). However, nearly all patients develop resistance. We designed a phase II multicenter study of enzalutamide in metastatic CRPC incorporating tissue and blood biomarkers to dissect mechanisms driving resistance.Patients and Methods:Eligible patients with metastatic CRPC underwent a baseline metastasis biopsy and then initiated enzalutamide 160 mg daily. A repeat metastasis biopsy was obtained at radiographic progression from the same site when possible. Blood for circulating tumor cell (CTC) analysis was collected at baseline and progression. The primary objective was to analyze mechanisms of resistance in serial biopsies. Whole-exome sequencing was performed on tissue biopsies. CTC samples underwent RNA sequencing.Results:A total of 65 patients initiated treatment, of whom 22 (33.8%) had received prior abiraterone. Baseline biopsies were enriched for alterations in AR (mutations, amplifications) and tumor suppression genes (PTEN, RB1, and TP53), which were observed in 73.1% and 92.3% of baseline biopsies, respectively. Progression biopsies revealed increased AR amplifications (64.7% at progression vs. 53.9% at baseline) and BRCA2 alterations (64.7% at progression vs. 38.5% at baseline). Genomic analysis of baseline and progression CTC samples demonstrated increased AR splice variants, AR-regulated genes, and neuroendocrine markers at progression.Conclusions:Our results demonstrate that a large proportion of enzalutamide-treated patients have baseline and progression alterations in the AR pathway and tumor suppressor genes. We demonstrate an increased number of BRCA2 alterations post-enzalutamide, highlighting the importance of serial tumor sampling in CRPC.

PURPOSESapanisertib is a kinase inhibitor that inhibits both mammalian target of rapamycin complex 1 (mTORC1) and mTORC2. In this multicenter, single-arm phase II trial, we evaluated the efficacy of sapanisertib in patients with treatment-refractory metastatic renal cell carcinoma (mRCC; NCT03097328 ).METHODSPatients with mRCC of any histology progressing through standard therapy (including prior mTOR inhibitors) had baseline biopsy and received sapanisertib 30 mg by mouth once weekly until unacceptable toxicity or disease progression. The primary end point was objective response rate by RECIST 1.1. Tissue biomarkers of mTOR pathway activation were explored.RESULTSWe enrolled 38 patients with mRCC (clear cell = 28; variant histology = 10) between August 2017 and November 2019. Twenty-four (63%) had received ≥ 3 prior lines of therapy; 17 (45%) had received prior rapalog therapy. The median follow-up was 10.4 (range 1-27.4) months. Objective response rate was two of 38 (5.3%; 90% CI, 1 to 15.6); the median progression-free survival (PFS) was 2.5 months (95% CI, 1.8 to 3.7). Twelve patients (32%) developed treatment-related grade 3 adverse events, with no grade 4 or 5 toxicities. Alterations in the mTOR pathway genes were seen in 5 of 29 evaluable patients ( MTOR n = 1, PTEN n = 3, and TSC1 n = 1) with no association with response or PFS. Diminished or loss of PTEN expression by immunohistochemistry was seen in 8 of 21 patients and trended toward shorter PFS compared with intact PTEN (median 1.9 v 3.7 months; hazard ratio 2.5; 95% CI, 0.9 to 6.7; P = .055).CONCLUSIONSapanisertib had minimal activity in treatment-refractory mRCC independent of mTOR pathway alterations. Additional therapeutic strategies are needed for patients with refractory mRCC.

PURPOSE Nearly all men with prostate cancer treated with androgen receptor (AR) signaling inhibitors (ARSIs) develop resistance via diverse mechanisms including constitutive activation of the AR pathway, driven by AR genomic structural alterations, expression of AR splice variants (AR-Vs), or loss of AR dependence and lineage plasticity termed neuroendocrine prostate cancer. Understanding these de novo acquired ARSI resistance mechanisms is critical for optimizing therapy. MATERIALS AND METHODS A novel liquid biopsy technology was used to collect mRNA from circulating tumor cells (CTCs) to measure expression of AR-Vs, AR targets, and neuroendocrine prostate cancer markers. An institutional review board–approved prospective cohort (N = 99) was used to identify patterns of gene expression. Two prospective multicenter phase II clinical trials of ARSIs for men with castration-resistant prostate cancer (ClinicalTrials.gov: NCT01942837 [enzalutamide, N = 21] and NCT02025010 [abiraterone, N = 27]) were used to further validate these findings. RESULTS Hierarchical clustering of CTC transcripts identified two distinct clusters. Cluster 2 (C2) exhibited increased expression of AR-regulated genes and was associated with worse overall survival (median 8.6 v 22.4 months; P < .01; hazard ratio [HR] = 3.45 [1.9 to 6.14]). In multivariable analysis, C2 was prognostic independent of other clinicopathologic variables. AR-V status was not significant when accounting for C2. Upon further validation in pooled multicenter phase II trials, C2 was associated with worse overall survival (15.2 months v not reached; P < .01; HR = 8.43 [2.74 to 25.92]), prostate-specific antigen progression-free survival (3.6 v 12 months; P < .01; HR = 4.64 [1.53 to 14.11]), and radiographic progression-free survival (2.7 v 40.6 months; P < .01; HR = 4.64 [1.82 to 17.41]). CONCLUSION We demonstrate that a transcriptional profile detectable in CTCs obtained from liquid biopsies can serve as an independent prognostic marker beyond AR-V7 in patients with metastatic prostate cancer and can be used to identify the emergence of multiple ARSI resistance mechanisms. This is currently being investigated in additional prospective trials.

Although therapeutic options for patients with advanced renal cell carcinoma (RCC) have increased in the past decade, no biomarkers are yet available for patient stratification or evaluation of therapy resistance. Given the dynamic and heterogeneous nature of clear cell RCC (ccRCC), tumor biopsies provide limited clinical utility, but liquid biopsies could overcome these limitations. Prior liquid biopsy approaches have lacked clinically relevant detection rates for patients with ccRCC. This study employed ccRCC‐specific markers, CAIX and CAXII, to identify circulating tumor cells (CTC) from patients with metastatic ccRCC. Distinct subtypes of ccRCC CTCs were evaluated for PD‐L1 and HLA‐I expression and correlated with patient response to therapy. CTC enumeration and expression of PD‐L1 and HLA‐I correlated with disease progression and treatment response, respectively. Longitudinal evaluation of a subset of patients demonstrated potential for CTC enumeration to serve as a pharmacodynamic biomarker. Further evaluation of phenotypic heterogeneity among CTCs is needed to better understand the clinical utility of this new biomarker., Circulating tumor cells (CTCs) were evaluated for their expression of programmed death ligand‐1 (PD‐L1) and human leukocyte antigen class I (HLA‐I), so that biomarkers of therapeutic resistance of clear cell renal cell carcinoma can be developed. CTCs were captured with antibody‐conjugated magnetic beads against EpCAM and CAIX then probed for CAXII and CK expression using microfluidic technology.

Purpose: Enzalutamide is a second-generation androgen receptor (AR) inhibitor that has improved overall survival (OS) in metastatic castration-resistant prostate cancer (CRPC). However, nearly all patients develop resistance. We designed a phase II multicenter study of enzalutamide in metastatic CRPC incorporating tissue and blood biomarkers to dissect mechanisms driving resistance. Patients and Methods: Eligible patients with metastatic CRPC underwent a baseline metastasis biopsy and then initiated enzalutamide 160 mg daily. A repeat metastasis biopsy was obtained at radiographic progression from the same site when possible. Blood for circulating tumor cell (CTC) analysis was collected at baseline and progression. The primary objective was to analyze mechanisms of resistance in serial biopsies. Whole-exome sequencing was performed on tissue biopsies. CTC samples underwent RNA sequencing. Results: A total of 65 patients initiated treatment, of whom 22 (33.8%) had received prior abiraterone. Baseline biopsies were enriched for alterations in AR (mutations, amplifications) and tumor suppression genes (PTEN, RB1, and TP53), which were observed in 73.1% and 92.3% of baseline biopsies, respectively. Progression biopsies revealed increased AR amplifications (64.7% at progression vs. 53.9% at baseline) and BRCA2 alterations (64.7% at progression vs. 38.5% at baseline). Genomic analysis of baseline and progression CTC samples demonstrated increased AR splice variants, AR-regulated genes, and neuroendocrine markers at progression. Conclusions: Our results demonstrate that a large proportion of enzalutamide-treated patients have baseline and progression alterations in the AR pathway and tumor suppressor genes. We demonstrate an increased number of BRCA2 alterations post-enzalutamide, highlighting the importance of serial tumor sampling in CRPC.

PURPOSE: Current first-line treatment options in patients with metastatic urothelial carcinoma (mUC) unfit to receive cisplatin-containing chemotherapy include PD-1/L1 inhibitors and carboplatin-containing chemotherapy. However, the optimal sequencing of these therapies remains unclear. MATERIAL AND METHODS: We conducted a multicenter retrospective analysis. Consecutive cisplatin-ineligible patients with mUC treated with first-line carboplatin-containing chemotherapy followed sequentially by second-line PD-1/L1 inhibitor, or the reverse order, were included. Patient demographics, objective response, time to treatment failure for first-line (TTF1) and second-line (TTF2) therapy, interval between end of first-line and initiation of second-line treatment (Interval(1L-2L)), and overall survival (OS) were collected. Multivariate analysis was conducted to examine the association of sequencing on OS. RESULTS: In this multicenter retrospective study, we identified 146 cisplatin-ineligible patients with mUC treated with first-line (1L) PD-1/L1 inhibitor therapy followed by second-line (2L) carboplatin-containing chemotherapy (Group 1, n=43) or the reverse sequence (Group 2, n=103). In the overall cohort, median age was 72, 76% were men, and 18% had liver metastasis. In both groups, objective response rates were higher with carboplatin-containing chemotherapy (45.6% 1L, 44.2% 2L) compared to PD-1/L1 inhibitors (9.3% 1L, 21.3% 2L). On multivariate analysis, treatment sequence was not associated with overall survival (HR 1.05, p=0.85). Site of metastasis was the only factor significantly associated with overall survival (p=0.002). CONCLUSIONS: In this biomarker-unselected cohort of cisplatin-ineligible patients with mUC, PD-1/L1 inhibitor followed by carboplatin-containing chemotherapy and the reverse sequence had comparable OS.

Background Cabozantinib is approved for the first and subsequent line treatment of metastatic clear-cell renal cell carcinoma (ccRCC) based on trials in which most patients were immune checkpoint blockade (ICB) naive. With an expanding role of ICB in earlier lines of therapy, we assessed activity of cabozantinib in patients with metastatic ccRCC after progressing on anti-PD-1/PD-L1–based ICBs. Methods We retrospectively analysed the clinical outcomes of 86 patients from 2 academic centres who received cabozantinib after progression on ICB alone, ICB in combination with vascular endothelial growth factor inhibitors (VEGFis) or ICB in combination with other therapies. Overall response rate (ORR, investigator assessed), time to treatment failure (TTF), overall survival (OS) and toxicities leading to dose reductions or cessation were evaluated. Results Eighty-six patients were included in the analysis; the median age was 63 years (range 33–84) and the median number of prior therapies was 2 (range 1–10). The type of prior ICB therapy was ICBs alone (64%), an ICB in combination with a VEGFi (29%) or ICBs in combination with other therapies (7%). At the time of cabozantinib treatment, 71% of patients were in the International Metastatic RCC Database Consortium good- or intermediate-risk groups. Approximately half of patients (52%) were started on cabozantinib at the full 60 mg daily dose. The ORR was 36% (95% confidence interval [CI] = 26–47%) with no complete response and 43% achieving stable disease; 21% had primary progressive disease. The median TTF was 6.5 months (95% CI = 5.3–8.5.). The median OS was 13.1 months (95% CI = 8.7-NR) with 55% (95% CI = 41–66%) OS rate at 12 months. Most common reasons for dose reductions were fatigue (27%), palmar-plantar erythrodysesthesia (16%) and diarrhoea (10%). Conclusions Cabozantinib is active in patients treated with prior ICB-based therapies, with no new safety signals. This study supports the use of cabozantinib after ICB-based therapies.

178 Background: Intensification of systemic therapy beyond ADT, with use of novel hormonal agents (NHAs), and radiotherapy (RT) to the prostate have a proven survival benefit in mHSPC. MDT has shown benefit in delaying need for ADT in omHSPC in phase 2 trials. Combination of fixed-duration systemic therapy with MDT (and RT to the prostate in de novo mHSPC) may produce long-term remission and treatment-free survival in selected patients with omHSPC. Methods: Patients with de novo or recurrent omHSPC treated at our institution between 2010-2020 with MDT (+/- prostate RT if de novo) and a fixed duration of systemic therapy completed by September 2022 were identified. There was no limit on number of metastases as long as all sites could be treated with MDT in the view of the treating physician. Oligometastases were defined as bone or soft tissue lesions beyond the pelvic lymph nodes identified on conventional scans (CT, bone scan, MRI) or PET (fluciclovine or PSMA). The primary outcome was freedom from biochemical recurrence (BCR), defined as PSA of >0.02 (if the patient had undergone prior radical prostatectomy) or >2+nadir (if the patient underwent RT) after completion of systemic therapy. Testosterone recovery was defined as serum testosterone >150ng/dL attained after completion of systemic therapy. BCR-free survival after completion of systemic therapy was estimated using the Kaplan Meier method. Results: 32 patients were included. Median age at diagnosis of mHSPC was 67 (range 52-78). 12 patients (38%) had de novo mHSPC while 20 (63%) had oligorecurrent HSPC. Detection of omHSPC was by conventional scans in 23 patients (72%) and by PET only in 9 (28%), and median number of oligometastases was 1 (range 1-6). Median PSA at start of therapy for omHSPC was 8.2ng/mL (range 0.4-1244), with systemic therapy most commonly comprising of ADT and a NHA (abiraterone, enzalutamide, apalutamide, n=26 [82%]); 6 patients (19%) had ADT alone. Median duration of systemic therapy was 24 months (range 6-36), with 3 men (9%) having received prior systemic therapy for mHSPC. MDT consisted of external beam RT (EBRT, n=10, 31%), EBRT + stereotactic body radiotherapy (SBRT, n=8, 25%), or SBRT alone (n=14, 44%). At a median follow-up of 44 months (range 24-127) and 20 months (2-103) after start and completion of systemic therapy respectively, 9 patients (28%) had BCR and 23 (72%) remained free of BCR, of whom 13 (57%) had testosterone recovery. The estimated 2-year BCR-free survival after completion of systemic therapy was 73% (95% CI 51-86). Conclusions: In this carefully selected cohort of men with omHSPC, estimated 2-yr BCR-free survival after completion of therapy was >70% with ~2 years of ADT +/- NHA along with MDT +/- prostate RT (if de novo). Longer follow-up is needed to determine whether this translates to a durable treatment-free remission, and possibly cure, in these patients with omHSPC.

108 Background: LuPSMA received FDA approval in March 2022 for patients with PSMA-positive metastatic castrate-resistant prostate cancer (mCRPC). Clinical implementation of this treatment requires multidisciplinary team (MDT) involvement and has been beset by challenges in drug supply. We established a joint DFCI GU/Nuclear Medicine Tumor Board (GU-NM TB) to review patients for therapy, and our initial experiences are described. Methods: A joint GU-NM TB was established. All patients with mCRPC who had received at least one prior chemotherapy and a novel hormonal agent were considered eligible and referred to TB through an online referral system after undergoing PSMA-PET/CT. Case details, including prior treatment history, performance status and organ function, and PET/CT imaging were reviewed at TB, with patients either being approved, deferred, or declined for LuPSMA therapy. Patients were scheduled for therapy on a first-come first-served basis. Treatment was delivered per standard-of-care at 180-200 millicurie doses every 6 weeks within NM. A questionnaire was sent to 25 referring physicians 2 months after implementation of the TB to evaluate the referral process. Results: Between May-September 2022, a total of 108 patients were referred for LuPSMA therapy. Median age at time of referral was 73 (range 52-93), and 90% of patients were Caucasian. Median duration between PSMA-PET/CT and TB review was 10 days (IQR 6-17). 84 patients (78%) were approved for therapy, 16 (15%) were deferred and 7 (6%) were declined (reasons including absence of prior chemotherapy, high risk for toxicities, poor performance status); 1 patient died before TB review. Prior therapies included docetaxel (84%), cabazitaxel (56%), abiraterone (67%), enzalutamide (57%), darolutamide (23%), radium-223 (21%) and apalutamide (7%). Median number of prior treatments was 4 (range 2-12). Sites of disease on PSMA-PET/CT included bone (81%), pelvic lymph nodes (42%), extrapelvic lymph nodes (88%), lung (27%) and liver (22%). As of September 2022, a total of 40 patients (48%) have received at least 1 cycle of therapy and 17 (20%) have received 2 cycles; 6 patients (7%) approved for therapy died before receiving 177Lu-PSMA-617. Of the patients that have received 1 cycle of therapy, median duration between TB acceptance and C1 was 52 days (range 32-114). Out of 13 survey respondents, all 13 (100%) reported that their overall experience of the referral process was positive or very positive, and 12 (92%) noted that the Tumor Board had provided additional clinical insights on occasion or frequently. Conclusions: Due to drug supply shortages

247 Background: The mainstay of therapy in metastatic prostate cancer is androgen receptor (AR) signaling inhibition. However, the emergence of early castration resistance or neuroendocrine transformation is associated with poor prognosis. Reliable biomarkers are needed to identify these patients and guide selection of clinical therapy. Methods: mRNA was isolated from EpCAM-positive circulating tumor cells (CTCs) isolated from patients with CSPC, CRPC, or NEPC to measure expression of KLK2, KLK3 (PSA), TMPRSS2, FOLH1 (PSMA), synaptophysin ( SYP), and chromogranin ( CHGA). Post-hoc retrospective analysis of an institutional review board–approved prospective cohort (N = 98) was performed to identify patterns of gene expression. Samples were considered AR+ if 3 of 4 AR pathway genes ( TMPRSS2, KLK2, KLK3, and FOLH1) were positive, and were considered NE+ if either or both SYP or CHGA were positive. Blood samples from two prospective clinical trials of men with mCRPC treated with abiraterone and enzalutamide, respectively, were analyzed to confirm results. Longitudinal samples were collected from 17 patients (6 NEPC and 11 Adenocarcinoma) and cell free DNA was isolated and sequenced using a novel targeted exon panel. Results: AR and/or NE positive patients were found to have a median overall survival (OS) of 8.58 months as compared to a median OS of 29.6 months in the AR and NE negative population (p

Background In metastatic urothelial carcinoma (mUC), predictive biomarkers that correlate with response to immune checkpoint inhibitors (ICIs) are lacking. Here, we interrogated genomic and clinical features associated with response to ICIs in mUC. Methods Sixty two mUC patients treated with ICI who had targeted tumour sequencing were studied. We examined associations between candidate biomarkers and clinical benefit (CB, any objective reduction in tumour size) versus no clinical benefit (NCB, no change or objective increase in tumour size). Both univariable and multivariable analyses for associations were conducted. A comparator cohort of 39 mUC patients treated with taxanes was analysed by using the same methodology. Results Nine clinical and seven genomic factors correlated with clinical outcomes in univariable analysis in the ICI cohort. Among the 16 factors, neutrophil-to-lymphocyte ratio (NLR) ≥5 (OR = 0.12, 95% CI, 0.01–1.15), visceral metastasis (OR = 0.05, 95% CI, 0.01–0.43) and single-nucleotide variant (SNV) count Conclusions This three-factor model includes genomic (SNV count >9) and clinical (NLR

Sipuleucel-T has demonstrated survival benefit in phase 3 trials but is utilized in few men with metastatic castration-resistant prostate cancer (mCRPC) in part due to low rates of PSA and objective response. Given the requirement to develop immune-mediated antitumor activity as vaccine-based therapy, sipuleucel-T may have delayed clinical activity. We explored this in a cohort of men from PROCEED (NCT01306890), an FDA-requested outcomes registry, and in a separate institutional cohort of mCRPC patients treated with sipuleucel-T at Dana-Farber Cancer Institute (DFCI).Men with mCRPC who received 3 infusions of sipuleucel-T and did not initiate a new mCRPC directed therapy for ≥6 months after completion of sipuleucel-T were included. All patients had rising PSA before starting sipuleucel-T and available post-treatment PSA measurements. Clinical outcomes of interest included: PSAOf 1902 men with mCRPC treated in PROCEED and 255 patients treated consecutively with sipuleucel-T between 4/2010 and 4/2017 at DFCI, 171 and 28 patients were included, respectively. In the PROCEED sample, PSAIn this analysis of mCRPC patients treated with sipuleucel-T who did not immediately initiate subsequent therapy using two datasets, delayed PSA response was observed in a subset of patients indicating delayed clinical activity.

5002 Background: In the phase 3 VISION study, gallium (68Ga) gozetotide (68Ga-PSMA-11) PET/CT imaging was used to determine eligibility for lutetium (177Lu) vipivotide tetraxetan (177Lu-PSMA-617). Given that 177Lu-PSMA-617 targets PSMA, we assessed the association between quantitative PSMA imaging parameters and treatment outcomes. Methods: In VISION, adults with mCRPC with ≥ 1 PSMA-positive (+) and no PSMA-negative lesions meeting the exclusion criteria were enrolled. In this sub-study, the association between imaging data from pre-enrollment 68Ga-PSMA-11 PET/CT scans of pts in the 177Lu-PSMA-617 group and clinical outcomes was assessed. Imaging data meeting quality requirements were analyzed for 548/551 pts. PSMA expression was quantified by 5 PET parameters: PSMA+ lesions by region, mean standardized uptake value (SUVmean), maximum SUV (SUVmax), PSMA+ tumor volume, and tumor load (PSMA+ tumor volume × SUVmean). Parameters were extracted from the whole body and 4 regions. Association between PET parameters and radiographic progression-free survival (rPFS; primary objective), overall survival (OS), objective response rate (ORR), and prostate–specific antigen 50 (PSA50) response was assessed. Results: Most pts (92.7%) had PSMA uptake in bone. In both the whole-body and regional analyses, statistically significant associations of PSMA PET parameters to clinical outcomes were observed (whole-body data shown in Table). Higher whole-body SUVmean was associated with improved clinical outcomes; pts in the highest quartile (SUVmean: rPFS, ≥ 10.2; OS, ≥ 9.9) had a median rPFS and OS of 14.1 and 21.4 months, vs 5.8 and 14.5 months for those in the lowest quartile (< 6.0; < 5.7), respectively. Absence of PSMA+ lesions in bone, liver, and lymph node, and lower PSMA+ tumor load, were indicators of good prognosis. Conclusions: Higher SUVmean is strongly associated with improved outcomes with 177Lu-PSMA-617; clinical efficacy for different SUV levels vs the SoC arm is being assessed. Data support use of 68Ga-PSMA-11 PET/CT scan to identify pts who will benefit from PSMA-targeted radioligand therapy.[Table: see text]

Sarcomatoid and rhabdoid (S/R) renal cell carcinoma (RCC) are highly aggressive tumors with limited molecular and clinical characterization. Emerging evidence suggests immune checkpoint inhibitors (ICI) are particularly effective for these tumors, although the biological basis for this property is largely unknown. Here, we evaluate multiple clinical trial and real-world cohorts of S/R RCC to characterize their molecular features, clinical outcomes, and immunologic characteristics. We find that S/R RCC tumors harbor distinctive molecular features that may account for their aggressive behavior, including BAP1 mutations, CDKN2A deletions, and increased expression of MYC transcriptional programs. We show that these tumors are highly responsive to ICI and that they exhibit an immune-inflamed phenotype characterized by immune activation, increased cytotoxic immune infiltration, upregulation of antigen presentation machinery genes, and PD-L1 expression. Our findings build on prior work and shed light on the molecular drivers of aggressivity and responsiveness to ICI of S/R RCC., Sarcomatoid and rhabdoid tumours are highly aggressive forms of renal cell carcinoma that are also responsive to immunotherapy. In this study, the authors perform a comprehensive molecular characterization of these tumours discovering an enrichment of specific alterations and an inflamed phenotype.

BackgroundCD73–adenosine signaling in the tumor microenvironment is immunosuppressive and may be associated with aggressive renal cell carcinoma (RCC). We investigated the prognostic significance of CD73 protein expression in RCC leveraging nephrectomy samples. We also performed a complementary analysis using The Cancer Genome Atlas (TCGA) dataset to evaluate the correlation of CD73 (ecto-5′-nucleotidase (NT5E), CD39 (ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1)) and A2 adenosine receptor (A2AR;ADORA2A) transcript levels with markers of angiogenesis and antitumor immune response.MethodsPatients with RCC with available archived nephrectomy samples were eligible for inclusion. Tumor CD73 protein expression was assessed by immunohistochemistry and quantified using a combined score (CS: % positive cells×intensity). Samples were categorized as CD73negative(CS=0), CD73lowor CD73high(< and ≥median CS, respectively). Multivariable Cox regression analysis compared disease-free survival (DFS) and overall survival (OS) between CD73 expression groups. In the TCGA dataset, samples were categorized as low, intermediate and highNT5E,ENTPD1andADORA2Agene expression groups. Gene expression signatures for infiltrating immune cells, angiogenesis, myeloid inflammation, and effector T-cell response were compared betweenNT5E,ENTPD1andADORA2Aexpression groups.ResultsAmong the 138 patients eligible for inclusion, ‘any’ CD73 expression was observed in 30% of primary tumor samples. High CD73 expression was more frequent in patients with M1 RCC (29% vs 12% M0), grade 4 tumors (27% vs 13% grade 3 vs 15% grades 1 and 2), advanced T-stage (≥T3: 22% vs T2: 19% vs T1: 12%) and tumors with sarcomatoid histology (50% vs 12%). In the M0 cohort (n=107), patients with CD73hightumor expression had significantly worse 5-year DFS (42%) and 10-year OS (22%) compared with those in the CD73negativegroup (DFS: 75%, adjusted HR: 2.7, 95% CI 1.3 to 5.9, p=0.01; OS: 64%, adjusted HR: 2.6, 95% CI 1.2 to 5.8, p=0.02) independent of tumor stage and grade. In the TCGA analysis, highNT5Eexpression was associated with significantly worse 5-year OS (p=0.008).NT5EandENTPD1expression correlated with higher regulatory T cell (Treg) signature, whileADORA2Aexpression was associated with increased Treg and angiogenesis signatures.ConclusionsHigh CD73 expression portends significantly worse survival outcomes independent of stage and grade. Our findings provide compelling support for targeting the immunosuppressive and proangiogenic CD73–adenosine pathway in RCC.

Sarcomatoid and rhabdoid (S/R) renal cell carcinoma (RCC) are highly aggressive tumors with limited molecular and clinical characterization. Emerging evidence suggests immune checkpoint inhibitors (ICI) are particularly effective for these tumors1–3, although the biological basis for this property is largely unknown. Here, we evaluate multiple clinical trial and real-world cohorts of S/R RCC to characterize their molecular features, clinical outcomes, and immunologic characteristics. We find that S/R RCC tumors harbor distinctive molecular features that may account for their aggressive behavior, including BAP1 mutations, CDKN2A deletions, and increased expression of MYC transcriptional programs. We show that these tumors are highly responsive to ICI and that they exhibit an immune-inflamed phenotype characterized by immune activation, increased cytotoxic immune infiltration, upregulation of antigen presentation machinery genes, and PD-L1 expression. Our findings shed light on the molecular drivers of aggressivity and responsiveness to immune checkpoint inhibitors of S/R RCC tumors.

511 Background: PD(L)1 inhibitors can achieve durable responses in aUC but only in a minority of patients (pts). Combination strategies with agents that “prime and stimulate” the immune system may improve outcomes. CV301 comprises 2 recombinant poxviruses, Modified Vaccinia Ankara (MVA) and Fowlpox (FPV), encoding the human transgenes for CEA, MUC-1, and a Triad of Co-stimulatory Molecules (TRICOM: ICAM-1, LFA-3, and B7-1). MVA-CV301 is used for priming and FPV-CV301 is used for booster doses. Preliminarily, BN-platform vaccine plus PD-(L)1 inhibitors exhibited synergistic preclinical anti-tumor efficacy and the combination of CV301 and anti-PD-(L)1 agent demonstrated an acceptable safety profile. We hypothesized that this combination would be safe and effective in cisplatin-ineligible or platinum-refractory pts with aUC. Methods: A Phase 2, single-arm multicenter trial was designed to study CV301 + atezo as 1st-line treatment in pts with aUC ineligible for cisplatin-based chemotherapy regardless of PD-L1 status (Cohort 1; C1) and in pts progressing on/after platinum-based chemotherapy (Cohort 2; C2). MVA-CV301 was given subcutaneously (SC) on Days 1 and 22 and FPV-CV301 SC from day 43 every 21 days for 4 doses, then every 6 weeks until 6 months, then every 12 weeks until 2 years. Atezo 1200mg IV was given every 21 days. Primary endpoint: objective response rate (ORR). Secondary endpoints: OS, PFS, response duration, AEs and antigen-specific T-cell responses to CEA and MUC-1 by ELISPOT. Using 1-sided α 2.5%/cohort, a 2-stage design with 14/19 and 13/22 stage 1/2 subjects, respectively, will achieve ≥70% power if the true ORR for C1 is 43% and C2 is 33%. 3 C1 and 2 C2 responders were required in stage 1 to move forward. Results: 43 evaluable pts were enrolled and received therapy: 19 in C1; 24 in C 2. Overall, 9 pts experienced ≥ Grade 3 AEs related to the combination of treatment: 5 in C1, and 4 in C2. In C1, 1 pt had partial response (PR), for ORR 5.3% (90%CI: 0.3, 22.6) and 5 (26.3%, 90%CI: 11.0, 47.6) had stable disease (SD) as best response. In C2, 1pt had CR and 1 had PR, for ORR 8.3% (90%CI: 1.5, 24.0) and 3 (12.5%, 90%CI: 3.5, 29.2) had SD as best response. Median PFS and OS in C1 were 2.0 mo and 13.8 mo, and in C2 1.95 and 8.13 mo, respectively. The trial was halted for futility. Responding pts in C2 exhibited T-cell responses to CEA and pts with SD exhibited responses to MUC-1. Conclusions: CV301 + atezo exhibited an acceptable safety profile but did not demonstrate sufficient efficacy in pts with aUC as 1st-line therapy in cisplatin-ineligible pts or in the platinum-refractory setting. The development of effective vaccines to generate robust and durable responses as single agents and/or combined with anti-PD(L)1 remains an unmet need in aUC. Clinical trial information: NCT03628716.

98 Background: P-PSMA-101 is an autologous CAR-T therapy targeting PSMA, with a high percentage of stem cell memory T cells (TSCM) associated with efficacy, safety, and bone homing (particularly relevant to prostate cancer). It is manufactured using a novel non-viral transposon system (piggyBac) that creates high TSCM products. Genes are inserted encoding a PSMA-targeted Centyrin CAR, iCasp9-based safety switch, and DHFR to purify CAR-T cells. P-PSMA-101 completely eliminated tumors in intractable murine models of prostate cancer, providing rationale for this phase 1 trial (NCT04249947). Methods: Patients with mCRPC treated with or not eligible for a CYP17 inhibitor or second-generation antiandrogen, and a taxane were enrolled. P-PSMA-101 was manufactured from apheresed T cells and administered IV following a standard 3-day cy/flu lymphodepletion regimen. Dose escalation from 0.25-15 x 106 cells/kg is planned. Results: As of September 30, 2021, P-PSMA-101 had been administered to 10 heavily pretreated patients (median 7 prior regimens; range 3-15). Single infusions of 0.25 (n=5) to 0.75 (n=5) x 106 cells/kg have been assessed, with dose escalation continuing. P-PSMA-101 cells were shown to expand in blood via qPCR assay, peaking 2-3 weeks after infusion, consistent with the high percentage of TSCM. Significant antitumor responses were seen in this preliminary data set. Declines in PSA were seen in 7 patients (>50% in 3 and >99% in 1). Of 4 patients who had pre- and post-treatment FDG and PSMA-PET imaging, 3 demonstrated marked to complete resolution of abnormal uptake at known metastatic disease sites, with concordance in bone and CT scans, and/or circulating tumor cells (CTC). In 1 case, post-treatment tumor biopsy demonstrated infiltration by P-PSMA-101 CAR-T cells and elimination of tumor cells (pathologic complete response). Safety was consistent with expectations for a CAR-T product. CRS was seen in 60% (10% Gr ≥3) of patients. DLT was seen in 1 patient with macrophage activation syndrome/uveitis, and was the only Gr ≥3 CRS event. Immune effector cell-associated neurotoxicity syndrome (ICANS) has not occurred. CRS marker elevations were modest (max IL-6: 642.6 pg/mL). The most common AEs were cytopenias, infections, and constitutional symptoms (Gr ≥3 60%, 10%, and 0%), as expected with lymphodepletion. Treatable related ocular AEs were noted in 3 patients. Conclusions: These results parallel preclinical findings that P-PSMA-101 can produce marked efficacy in mCRPC, and very low doses are highly efficacious, consistent with unique product attributes such as the TSCM phenotype and bone tropism. This is the first report demonstrating profound antitumor effects of a novel PSMA-directed CAR-T-cell platform with concordant biochemical, radiographic, and pathologic parameters, demonstrating that therapeutic benefit of unarmored CAR-T cells in a major solid tumor is possible. Clinical trial information: NCT04249947.

528 Background: The BLASST-1 study is multi-center phase II trial evaluating the combination of nivolumab (N) with gemcitabine-cisplatin (GC) as a neoadjuvant therapy for patients (pts) with MIBC undergoing radical cystectomy (RC). The primary endpoint was pathologic down staging (PaR; ≤pT1N0). Safety, Relapse-free survival (RFS), Progression-free survival (PFS) and biomarker analyses were secondary endpoints. We previously reported a PaR rate of 65.8% and pCR rate of 49%. There were no safety concerns or delays to surgery. (ASCO GU 2020) Here, we correlate PaR with biomarkers (Tumor mutational burden (TMB), PD-L1 and molecular subtypes) and provide updated clinical follow-up (FU) data. Methods: Forty-one pts with MIBC (cT2-T4a, N≤1, M0) and candidates for RC were enrolled between Feb 2018 and June 2019; (cT2N0 90%, cT3N0 7%, cT4N1 3%). Pts received C (70mg/m2) IV on D1, G (1000mg/m2) on D1, D8 and N (360 mg) IV on D8 every 21 days for 4 cycles followed by RC within 8 weeks. For RNA-based analysis, GeneChip Human Exon 1.0 ST Array (Affymetrix) was used; baseline tumors from 37 patients passed quality control and had available transcriptome data. A cohort (n=223) of patients treated with NAC+RC was used as a comparator for molecular subtyping analysis. DNA was extracted from baseline pre-treatment tumor samples and sequenced to an average depth of 150X and the DNA extracted from matched normal tissue (peripheral blood) to a mean depth of 50X. PD-L1 expression was assessed using IHC 28-8 antibody on baseline tumors. Results: At a median FU of 15.8 months,12-month RFS rate was 85.4% and PFS including death from any cause was 83%. There were no long-term safety concerns. Molecular subtyping found patients with a basal-type tumor (Basal or Claudin-low) had a more favorable overall PaR in 13/18 = 73% with PaR in 9/13 in basal (69%) and 4/5 in claudin-low (80%) compared to overall PaR of 58% for the luminal-type tumors (Luminal or Infiltrated luminal) with a breakdown of PaR in 5/8 (63%) in luminal and 6/11 (54%) in infiltrated luminal. In contrast, in the comparator NAC cohort, the PaR rates were similar for basal-type and luminal-type tumors, with 44% and 48% respectively. There was no correlation of PaR with TMB or PD-L1 expression from bassline pre-treatment tumors. Biomarker analyses from residual tumors in RC tissues are ongoing. Conclusions: The combination of N+GC was safe and efficacious in MIBC with encouraging outcomes of pathologic down staging and relapse-free survival at a median FU of 15.8 months. Molecular subtyping results suggest basal-type tumors may respond more favorably to this chemo-immunotherapy treatment regimen. Clinical trial information: NCT03294304.

145 Background: In the phase 3 CHAARTED trial pts with mHSPC treated with ADT + D had an improved overall survival (OS) and longer time to castrate resistant prostate cancer (TTCRPC) than pts treated with ADT alone. We aimed to define the association of BTM levels with pt outcomes recognizing both ADT and bone metastases impact bone turnover. Methods: Serum samples were collected at baseline (BL) (within 28 days of starting ADT) in 233 (116 in ADT, 117 in ADT+D) pts and at week 24 in 423 (224 ADT+D, 199 ADT) pts. Samples were analyzed for osteocalcin (OC), osteoprotegrin (OPG), sclerostin (SL), RANKL and bone alkaline phosphatase (BALP). Cox proportional hazards models were used to assess the prognostic and predictive effects of the BTM in terms of OS and TTCPRC. Results: Whereas BALP baseline (BL) level < BL median was associated with longer OS independent of therapy (HR 0.44 95% CI 0.31-0.63, p BL median and BL RANKL < BL median were associated with longer OS in the ADT+D arm (HR 0.54 95% CI 0.32-0.9, p=0.015 and HR 1.69 95% CI 1,03-2.79, p=0.037) but not in the ADT alone arm (HR 0.75, 95% CI 0.45 − 1.25, p=0.271 and HR 1.06 95% CI 0.65 − 1.73 p=0.827). Changes in markers from BL to week 24 varied based on treatment and volume of disease with statistically significant changes noted (Table). A rise in OC or BALP on therapy from BL to week 24 was associated with improved TTCRPC and OS (OC: HR(TTCRPC) 0.792, p=0.033, HR(OS) 0.78 p=0.047; BALP: HR(TTCRPC) 0.82, p=0.03, HR (OS) 0.79, p=0.013) controlling for week 24 levels. However higher absolute OC and BALP levels at week 24 were associated with worse outcomes. (OC: HR(TTCRPC) 1.37, p=0.003, HR(OS)1.38, p=0.006; BALP: HR(TTCRPC) 1.54, p=0.007, HR(OS) 1.77, p=0.001). Conclusions: The BL finding with BALP are consistent with higher BALP being a poor prognostic marker. The BL OPG and RANKL findings suggest these markers might identify men who benefit from addingf D to ADT. The paradoxical improved survival with a rise in OC and BALP on therapy but worse outcomes with absolute higher levels at week 24 highlights complex dynamics of bone turnover related to varied impact from ADT, bone healing when responding to therapy versus active cancer. Clinical trial information: NCT00309985. [Table: see text]

Purpose FGFR3-TACC3 (fibroblast growth factor receptor 3–transforming acidic coiled coil-containing protein 3) fusions have recently been identified as driver mutations that lead to the activation of FGFR3 in bladder cancer and other tumor types and are associated with sensitivity to tyrosine kinase inhibitors. We examined the clinical and molecular characteristics of patients with FGFR3-TACC3 fusions and hypothesized that they are enriched in a subset of patients with bladder cancer. Materials and Methods We correlated somatic FGFR3-TACC3 fusions with clinical and molecular features in two cohorts of patients with bladder cancer. The first cohort consisted of the muscle-invasive bladder cancer (MIBC) data set (n = 412) from The Cancer Genome Atlas. The second cohort consisted of patients with MIBC or high-grade non-MIBC at the Dana-Farber Cancer Institute that had targeted capture sequencing of a selected panel of cancer genes (n = 356). All statistical tests were two sided. The clinical response of one patient with FGFR3-TACC3 bladder cancer to an FGFR3 inhibitor was investigated. Results Overall, 751 patients with high-grade bladder cancer without FGFR3-TACC3 fusions and 17 with FGFR3-TACC3 fusions were identified in the pooled analysis of the data sets from The Cancer Genome Atlas and the Dana-Farber Cancer Institute. FGFR3-TACC3 fusions were enriched in patients age ≤ 50 years versus age 51 to 65 years versus those older than 65 years (pooled, P = .002), and were observed in four (12%) of 33 patients age ≤ 50 years in the pooled analysis. Similarly, FGFR3-TACC3 fusions were significantly more common in Asians (13%) compared with African Americans (4%) and whites (2%; pooled, P < .001), as well as in never smokers (5.6%) compared with ever smokers (1.1%; pooled, P < .001). One patient with the fusion who was treated with an FGFR3 inhibitor achieved complete remission for 10 months. Conclusion Clinical testing to identify FGFR3 fusions should be prioritized for patients with bladder cancer who are younger, never smokers, and/or Asian.

Programmed death 1 (PD-1) and PD ligand 1 (PD-L1) inhibitors have shown activity in metastatic clear cell renal cell carcinoma (ccRCC). Data on the activity of these agents in patients with non–clear cell RCC (nccRCC) or patients with sarcomatoid/rhabdoid differentiation are limited. In this multicenter analysis, we explored the efficacy of PD-1/PD-L1 inhibitors in patients with nccRCC or sarcomatoid/rhabdoid differentiation. Baseline and follow-up demographic, clinical, treatment, and radiographic data were collected. The primary endpoint was objective response rate. Secondary endpoints include time-to-treatment failure (TTF), overall survival (OS), and biomarker correlates. Forty-three patients were included: papillary (n = 14; 33%), chromophobe (n = 10; 23%), unclassified (n = 9; 21%), translocation (n = 3; 7%), and ccRCC with sarcomatoid differentiation (n = 7, 16%). Of those 43 patients, 11 patients (26%) had sarcomatoid and/or rhabdoid differentiation (n = 7 with ccRCC; n = 4 nccRCC). Overall, 8 patients (19%) objectively responded, including 4 patients (13%) who received PD-1/PD-L1 monotherapy. Responses were observed in patients with ccRCC with sarcomatoid and/or rhabdoid differentiation (n = 3/7, 43%), translocation RCC (n = 1/3, 33%), and papillary RCC (n = 4/14, 29%). The median TTF was 4.0 months [95% confidence interval (CI), 2.8–5.5] and median OS was 12.9 months (95% CI, 7.4–not reached). No specific genomic alteration was associated with clinical benefit. Modest antitumor activity for PD-1/PD-L1–blocking agents was observed in some patients with nccRCC. Further prospective studies are warranted to investigate the efficacy of PD-1/PD-L1 blockade in this heterogeneous patient population. Cancer Immunol Res; 6(7); 758–65. ©2018 AACR.

Purpose of review There are currently limited data to guide the optimal management of patients with low-volume metastatic castration-resistant prostate cancer (mCRPC). In this review, we critically assess the most relevant clinical data, and discuss opportunities for advancing therapeutic options in this patient population. Recent findings Over the past decade, treatment options for mCRPC have expanded beyond taxanes to include abiraterone/prednisone, enzalutamide, sipuleucel-T, and radium-223. However, only a subset of patients in the landmark phase 3 studies would meet criteria consistent with low-volume mCRPC, and optimal treatment approach for this patient population is unclear. There is emerging evidence that mCRPC patients who harbor low-volume or indolent disease may derive the most benefit from immunotherapy. Whereas prospective data are lacking, stereotactic body radiation appears to be well tolerated and effective for local control of metastases in oligometastatic CRPC. Summary Prospective studies are needed to establish optimal therapeutic approaches in carefully selected low-volume mCRPC patients. Advances in functional imaging and molecular profiling should provide opportunities to optimize patient selection for effective treatment strategies.

PURPOSE In this multicenter phase II trial, we evaluated atezolizumab combined with bevacizumab in patients with advanced renal cell carcinoma (RCC) with variant histology or any RCC histology with ≥ 20% sarcomatoid differentiation. PATIENTS AND METHODS Eligible patients may have received previous systemic therapy, excluding prior bevacizumab or checkpoint inhibitors. Patients underwent a baseline biopsy and received atezolizumab 1,200 mg and bevacizumab 15 mg/kg intravenously every 3 weeks. The primary end point was overall response rate (ORR) by RECIST version 1.1. Additional end points were progression-free survival (PFS), toxicity, biomarkers of response as determined by programmed death-ligand 1 (PD-L1) status, and on-therapy quality-of-life (QOL) metrics using the Functional Assessment of Cancer Therapy Kidney Symptom Index-19 and the Brief Fatigue Inventory. RESULTS Sixty patients received at least 1 dose of either study agent; the majority (65%) were treatment naïve. The ORR for the overall population was 33% and 50% in patients with clear cell RCC with sarcomatoid differentiation and 26% in patients with variant histology RCC. Median PFS was 8.3 months (95% CI, 5.7 to 10.9 months). PD-L1 status was available for 36 patients; 15 (42%) had ≥ 1% expression on tumor cells. ORR in PD-L1–positive patients was 60% (n = 9) v 19% (n = 4) in PD-L1–negative patients. Eight patients (13%) developed treatment-related grade 3 toxicities. There were no treatment-related grade 4-5 toxicities. QOL was maintained throughout therapy. CONCLUSION In this study, atezolizumab and bevacizumab demonstrated safety and resulted in objective responses in patients with variant histology RCC or RCC with ≥ 20% sarcomatoid differentiation. This regimen warrants additional exploration in patients with rare RCC, particularly those with PD-L1–positive tumors.

Background Antibiotic use alters commensal gut microbiota, which is a key regulator of immune homeostasis. Objective To investigate the impact of antibiotic use on clinical outcomes in metastatic renal cell carcinoma (mRCC) patients treated with systemic agents. Design, setting, and participants We analyzed two cohorts: an institutional cohort (n = 146) receiving programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1)-based immune checkpoint inhibitors (ICIs) and a trial-database cohort (n = 4144) receiving interferon-α (n = 510), mammalian target of rapamycin (mTOR) inhibitors (n = 660), and vascular endothelial growth factor targeted therapies (VEGF-TT; n = 2974) on phase II/III clinical trials. Outcomes measurements and statistical analysis The association of antibiotic use (defined as use from 8 wk before to 4 wk after the initiation of anticancer therapy) with progression-free survival (PFS) and overall survival (OS) was evaluated using Cox regression, adjusted for known prognostic factors including International Metastatic RCC Database Consortium risk factors. Results and limitations Most patients were male, had clear cell histology, and were at an intermediate risk. Overall, in the institutional cohort, objective response rate (ORR) was 30%, PFS was 7.2 mo, and 1-yr OS was 77%. Antibiotic users (n = 31, 21%) had a lower ORR (12.9% vs 34.8%, p = 0.026) and shorter PFS (adjusted hazard ratio [HR] = 1.96, 95% confidence interval [CI] 1.20–3.20, p = 0.007) than antibiotic nonusers. In the trial-database cohort, antibiotic use (n = 709, 17%) adversely impacted OS in patients treated with interferon (HR = 1.62, 95% CI 1.13–2.31, p = 0.008) or with VEGF-TT and prior cytokines (HR = 1.65, 95% CI 1.04–2.62, p = 0.033), but not patients treated with mTOR inhibitors or VEGF-TT without prior cytokines. Limitations include retrospective design, and limited details regarding concomitant medications and antibiotic indication/duration. Conclusions Antibiotic use appears to reduce the efficacy of immunotherapy-based regimens in mRCC. The modulation of gut microbiota may play an important role in optimizing outcomes of patients treated with ICIs. Patient summary We evaluated metastatic renal cell carcinoma patients and found that those who were treated with immunotherapy had worse outcomes if they also received antibiotics at the start of treatment. This study highlights the importance of judicious antibiotic use.

98 Background: Treatment (tx) options for patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) to bone are limited. Radium-223 (R223) has demonstrated overall survival (OS) benefit, but objective clinical responses to R223 or the anti-PD1 checkpoint inhibitor (CPI) pembrolizumab (pem) are infrequent. As R223 may increase immunogenicity of mCRPC to bone and increase activity of CPI, we undertook a Phase 2 study to assess safety of the combination and differences in immune cell infiltrate in bone biopsies (bx) and preliminary clinical activity of R223 + pem vs. R223 alone. Methods: Eligibility required mCRPC to bone with no visceral metastases (mets) or lymph nodes > 2 cm, ECOG PS 0 or 1, Hgb ≥ 9 g/dL, and no prior R223 or CPI. Pts underwent bone bx at screening and at 8 wks. Pts were stratified by alkaline phosphatase ≥220 vs. < 220 U/L and high vs. low volume bony mets (CHAARTED criteria) and randomized 2:1 to receive R223 55 kBq/kg q4wks + pem 200 mg q3wks (Arm A) or R223 55 kBq/kg q4wks alone (Arm B). If restaging after 3 doses R223 showed at least stable disease, pts in Arm A continued pem alone until progressive disease (PD). Upon PD, R223 was resumed if no new visceral mets. Pts continued tx until clinical/radiologic PD, unacceptable toxicity or completion of 6 R223 doses. The primary endpoint was difference in CD4+ and CD8+ T-cell infiltrate in 8 wk vs. baseline bx; secondary endpoints were safety/tolerability, radiographic progression-free survival (rPFS) and OS. Exploratory endpoints included PSA response and rate of symptomatic skeletal events (SSEs). Results: Of 45 pts enrolled, 42 received study tx (29 Arm A, 13 Arm B) and were eligible for analysis. 21 pts in Arm A and 5 in Arm B had evaluable paired bone bx. Median fold-change of proportion of CD4+ T-cells/total cell count from baseline to 8 wks was 0.90 (range 0.0-26.6) in Arm A and 0.40 (0.0-13.0) in Arm B (P = 0.87); for CD8+ cells, median 0.67 (0.0-40.4) in Arm A and 0.40 (0.1-28.8) in Arm B (P = 0.77). Grade 3 treatment-related non-hematologic adverse events (AEs) occurred in 3 pts (10%) in Arm A (pneumonitis, diarrhea, AST increased); none in Arm B. Median rPFS was 6.7 mo (95% CI 2.7-11.0 mo) in Arm A and 5.7 mo (2.6-NR) in Arm B. Median OS was 16.9 mo (12.7-NR) in Arm A and 16.0 mo (9.0-NR) in Arm B. 3 pts (10%) in Arm A and 0 in Arm B had PSA reduction of ≥ 50%. SSE rate was 38% in Arm A and 54% in Arm B, with pathologic fractures in 0% of pts in Arm A and 23% in Arm B. Conclusions: In the 62% of treated pts with evaluable paired bx at baseline and after 8 wks, there was no evidence of increased CD4+ or CD8+ T-cell infiltration with R223 + pem. Additional biomarker analyses will be presented. This study revealed that R233 + pem did not result in unexpected AEs, but did not lead to prolonged rPFS or OS compared to R223 alone to support this two-drug combination in a biomarker-unselected population in this setting. Clinical trial information: NCT03093428.

e19390 Background: DD-MVAC and GC are commonly used NAC regimens for MIBC. While efficacy across studies appears similar, resource utilization (RU) burden and cost efficacy have not been compared. Methods: We assessed RU and cost effectiveness of NAC with GC vs DD-MVAC among MIBC patients (pts) treated at Dana-Farber. Data on chemotherapy administered, supportive medications, relevant procedures, hospitalizations, clinic, infusion, and emergency room (ER) visits were collected retrospectively. Unit costs for each RU component were sought from the Centers for Medicare and Medicaid Website as well as relevant published sources. Utilization was compared between MVAC and GC using multivariate quantile regression (QR) analysis. Results: 147 pts were included; 51 received DD-MVAC and 86 GC. Baseline characteristics were similar, except lower mean age (59 vs 67 years, p < 0.001) and higher proportion of ECOG-PS = 0 (96.1% vs 60.5%, p < 0.001) for DD-MVAC. The mean cumulative cisplatin dosage was similar (DD-MVAC = 284 mg/m2, GC = 257 mg/m3). More DD-MVAC pts required G-CSF analogues (100% vs 32.6%, p < 0.001), central line placement (28.6% vs 11.8%, p = 0.017), and ER visits (35% vs 18%, p = 0.048). Infusion visits (12 vs 8/pt) and cardiac imaging (0.98 vs 0.58/pt, p < 0.001) were higher for DD-MVAC, whereas GC pts required more frequent clinic visits (mean of 9 vs 5/pt), chemotherapy cycle delays (30.2% vs 9.8%, p = 0.008) and hospitalization days (mean of 0.88 vs 0.49/pt). After adjusting for PS, the mean total cost/pt was higher for DD-MVAC ($17360 vs $12112, p < 0.001). Age was not statistically significant in the QR model (p = 0.628). Conclusions: DD-MVAC and GC exhibit different RU characteristics as NAC for MIBC. Although excess RU did not clearly favor one regimen, adjustment for PS indicated significant decrease in healthcare costs by approximately 30% using GC compared to DD-MVAC. Given that similar overall delivery of cumulative cisplatin dosage was feasible with both regimens, the values and costs affixed to different resources may impact the selection of DD-MVAC vs GC. Limitations were retrospective design and costs being specific to the US.

e17588 Background: Clinical trials of sip-T predominately included white men (over 90%). Previously we explored outcomes with sip-T in white and black patients (pts) (Kantoff PW, NEJM 2010; Sartor AO, ASCO 2019, #5035). In this retrospective analysis of data from electronic medical record and practice management systems, we explored the hypothesis that Asian and white pts who receive sip-T for CRPC exhibit similar overall survival. Methods: Data came from > 100 US community urology practices, predominantly large urology group practice associations. White and Asian pts were matched based on 5 criteria: sip-T treatment year; treatment pattern for oral and sip-T; metastatic site (Bone v. Nodal v. Visceral); prostate-specific antigen (PSA) within 10%; and age at treatment. Parameters retrieved include those listed in the table. Overall survival (OS) was analyzed using Kaplan Meier (KM) methodology with Cox Proportional Hazards Modelling used to generate the hazard ratio (HR) with Asians as the reference. Descriptive summary statistics were generated for other parameters. Results: The analysis identified 102 white and 77 Asian pts; treatment ranged from 2012 to 2019 with 60% receiving sip-T after 2016, impacting the ability to examine long-term outcomes. Characteristics of the 2 groups were broadly similar, although more Asians had Gleason scores ≥8 than whites (Table). In the KM analysis, most pts were censored. While the KM survival curves separate around month 25, favoring Asian pts, the difference is not significant (HR, 0.69 [95% CI: 0.4, 1.4]; P = 0.277). Conclusions: These real-world data do not show a significant difference in OS between Asian and white men. Both groups exhibited relatively low median PSAs near 5 ng/mL, an observation correlated with longer OS in previous studies. [Table: see text]

5005 Background: Nivo + Ipi is an established first-line treatment (tx) for advanced RCC. We hypothesized that the addition of CTLA-4 blockade may not be required for all patients (pts). Furthermore, the optimal duration of Nivo maintenance in responding pts is unknown. In this phase II response-adaptive trial, we investigate the sequential addition of 2 doses of Ipi to induce response in Nivo non-responders (NR) and duration of Nivo in responding pts (NCT03203473). Methods: We enrolled pts with advanced RCC with no prior checkpoint inhibitor exposure. All pts received Nivo alone with subsequent arm allocation based on RECISTv1.1 response within 6 months (mos) of tx. Pts with a confirmed partial response (PR) or complete response (CR) within 6 months (mos) discontinued Nivo and were observed (Arm A). Arm A pts reinitiated Nivo if they developed progressive disease (PD); Ipi was added to Nivo if PD persisted or recurred. Pts with stable disease (SD) or PD after no more than 6 mos of Nivo alone received 2 doses of Ipi (Arm B). The primary endpoints were the proportion with PR/CR at 1-year (yr) after Nivo discontinuation (Arm A) and proportion of Nivo NR who convert to PR/CR after adding Ipi (Arm B). Results: 83 pts initiated tx of whom 99% had ECOG 0-1, 96% clear cell RCC, 51% tx-naïve, and 69% IMDC intermediate/poor risk. Median follow-up was 17.0 mos. 15 pts were not allocated to an arm [7 withdrew for PD, 7 withdrew for toxicity, 1 still on tx with unconfirmed PR (uPR)]. At 6 mos, induction Nivo resulted in a confirmed PR in 11% of pts (n=9/83): 12% (n=5/42) tx-naïve, 10% (4/41) prior tx, 8% (n=1/13) favorable risk, 11% (n=8/70) intermediate/poor risk (Table). 11 pts (13%: 9 PR, 1 uPR, 1 SD) were allocated to Arm A, of whom 5 (45%, 90% CI 20-73%) remained off Nivo at ≥ 1 yr. Of 57 pts (69%) allocated to Arm B, 2 pts converted to a PR (4%, 90% CI 1-11%), both of whom had prior tx and PD as best response to Nivo alone. Grade 3-4 treatment related adverse events (TrAE) occurred in 7% (n=6/83) on induction Nivo and in 23% (n=13/57) on Arm B (Nivo + Ipi). Conclusions: We cannot currently recommend a strategy of Nivo followed by response-based addition of Ipi due to the absence of CR and low PR/CR conversion rate (4%). Though a subset of pts treated with Nivo alone can maintain durable responses off tx at 1-yr, early Nivo discontinuation in the absence of toxicity cannot currently be recommended. Investigation into biomarkers to guide tx is ongoing. Clinical trial information: NCT03203473 . [Table: see text]

e17044 Background: Preclinical data indicate that angiotensin inhibition may improve drug delivery by enhancing tumor perfusion partly by downregulating transforming growth factor (TGF)-β. Since (TGF)-β appears to be associated with resistance in patients with mUC receiving PD1/L1 inhibitors, we investigated whether angiotensin converting enzyme inhibitors (ACEI) and angiotensin receptor blockers (ARBs) may enhance the outcomes of mUC pts receiving PD1/L1 inhibitors. Methods: Data from mUC pts who received PD1/L1 inhibitors at the Dana-Farber Cancer Institute (DFCI) was obtained. Data for ACEI and ARB administration was collected with concurrent administration defined as ongoing therapy from the time of starting PD1/L1 inhibitor treatment. A Cox logistic regression was used to investigate the impact of concurrent ACEI/ARB on any regression of tumor (ART, any decrease in size of tumor on scan) defined as any tumor regression after controlling for known prognostic factors (performance status, sites of metastasis, neutrophil/lymphocyte ratio, platelet count, hemoglobin). Results: Data was available for 178 pts with mUC who received pembrolizumab (79), atezolizumab (83), nivolumab (15), and durvalumab (1). Prior platinum chemotherapy was administered in 153 pts (86%). 33 pts (18.5%) received AECI/ARBs: 24 pts (13.5%) received ACEI and 9 pts (5.1%) received ARBs. Of 145 patients who did not receive an ACE-inhibitor nor an ARB, 49 (33.8%) patients experienced ART and their median overall survival (OS) was 9.1 months. Among/33 patients who did receive an ACEI or an ARB, 17 (51.5%) exhibited ARTand their median OS was 17.0 months. Multivariable analysis controlling for known prognostic factors revealed that patients who received ACE inhibitors or ARBs had greater ART (HR 3.0 [95% CI 1.25-7.17], p = 0.014) and improved OS, (HR 0.49 [95% CI 0.28-0.88] p = 0.016). Conclusions: In this hypothesis-generating study, concurrent angiotensin inhibitors including ACEI or ARBs were associated with significantly better outcomes in mUC pts receiving PD-1/L1 inhibitors. These results require validation in a larger mUC dataset in conjunction with probing the effect in other malignancies.

BackgroundImmune checkpoint inhibitors (ICIs) are associated with immune-related adverse events (irAEs). Although the incidence and prevalence of irAEs have been well characterized in the literature, less is known about the cumulative incidence rate of irAEs. We studied the cumulative incidence of irAEs, defined as the probability of irAE occurrence over time and the risk factors for irAE development in metastatic urothelial carcinoma (mUC) and renal cell carcinoma (mRCC) patients treated with ICIs.MethodsWe identified a cohort of patients who received ICIs for mUC and mRCC. irAEs were classified using Common Terminology Criteria for Adverse Event (CTCAE) V.5.0 guidelines. The monthly incidence of irAEs over time was reported after landmark duration of therapy. Cumulative incidence of irAEs was calculated to evaluate the time to the first occurrence of an irAE accounting for the competing risk of death. Prognostic factors for irAE were assessed using the Fine and Gray method.ResultsA total of 470 patients were treated with ICIs between July 2013 and October 2018 (mUC: 199 (42.3%); mRCC: 271 (57.7%)). 341 (72.6%) patients received monotherapy, 86 (18.3%) received ICIs in combination with targeted therapies, and 43 (9.2%) received dual ICI therapy. Overall, 186 patients (39.5%) experienced an irAE at any time point. Common irAEs included hypothyroidism (n=42, 22.6%), rush and pruritus (n=36, 19.4%), diarrhea/colitis (n=35, 18.8%), transaminitis (n=32, 17.2%), and pneumonitis (n=14, 7.5%). Monthly incidence rates decreased over time; however, 17 of 109 (15.6%, 95% CI: 9.4% to 23.8%) experienced their first irAE at least 1 year after treatment initiation. No differences in cumulative incidence were observed based on cancer type, agent, or irAE grade. On multivariable analysis, combined ICI therapy with another ICI or with targeted therapy (pConclusionsThis study quantitates the incidence of developing irAEs due to ICI conditioned on time elapsed without irAE development. Although the monthly incidence of irAEs decreased over time on therapy, patients can still develop delayed irAEs beyond ICI discontinuation, and thus, continuous vigilant monitoring is warranted.

474 Background: DD-MVAC and GC are commonly used NAC regimens for MIBC. While efficacy across studies appears similar, the resource utilization burdens have not been compared. Methods: We assessed the resource utilization and cost effectiveness of NAC with GC vs DD-MVAC for MIBC patients (pts) treated at Dana-Farber. Data on chemotherapy administered, supportive medications, relevant procedures, hospitalizations, clinic, infusion, and emergency room visits were collected retrospectively. Results: 147 patients were included, 51 in the DD-MVAC and 86 in the GC group. The two groups had similar baseline pt characteristics except lower mean age (59 vs 67 years, p2, GC= 257 mg/m3). The DD-MVAC group exhibited a greater use of G-CSF analogues (100% vs 32.6%, p < 0.001), central line placement (28.6% vs 11.8%, p = 0.017), infusion visits/pt (12 vs 8), ER visits (35% vs 18%, p = 0.048), and cardiac imaging (0.98 vs 0.58/pt, p

439 Background: Cisplatin-based neoadjuvant chemotherapy (NAC) in MIBC improves survival which correlates with pathologic response (PaR) at radical cystectomy (RC). The combination of immunotherapy and NAC may improve PaR and outcomes in MIBC. We tested the efficacy and safety of nivolumab (N) with gemcitabine-cisplatin (GC) as neoadjuvant therapy for MIBC in our phase II trial (NCT03294304). Methods: Eligible pts with MIBC (cT2-T4a, N≤1, M0) who were candidates for RC were enrolled. Pts received C (70mg/m2) IV on D1, G (1000mg/m2) on D1,D8 and N (360 mg) IV on D8 every 21 days for 4 cycles followed by RC within 8 weeks. The primary endpoint was PaR (≤pT1,N0). Secondary objectives were safety of GC+N and PFS at 2 years. The correlative objectives based on pre-treatment biopsies were correlation of PaR with 1) WGS 2) molecular subtypes of BC; 3) PD-L1 expression; 4) baseline TILs, CD3, CD8 and CD56.. Evaluable pts. should have received at least 1 dose of N. PaR will be summarized by the PaR rate as estimated by the sample proportion with exact 95% confidence intervals. We specified a null PaR of 0.35 and an alternative hypothesis of 0.55; we will reject the null hypothesis if at least 20 of 41 pts. have a PaR. Results: Between Feb 2018 and June 2019, 41 pts. were enrolled (cT2N0 90%, cT3N0 7%, cT4N1 3%); 2 patients refused surgery but were included in ITT population. PaR was observed in 27/41 pts. (65.8%), including pts with N1 disease. The combination was safe with manageable toxicities and no deaths from treatment. Majority of AEs were from GC; the overall rates of grade 3-4 AEs was 20%, majority being neutropenia, thrombocytopenia and renal insufficiency. Immune related AEs were seen in 3 patients, 2 had "adenitis" which wasymptomatic,1 pt developed Guillian Barre Syndrome after surgery, which resolved with IVIG; and none of them required steroids. There was no delay in time to RC and no unexpected surgical complications from treatment. Patients are being followed for progression and survival. Correlative work is ongoing. Conclusions: Neoadjuvant N+GC is safe and effective in MIBC with significant pathologic downstaging rates and no added toxicities or delay to surgery. Clinical trial information: NCT03294304.

507 Background: There is no established neoadjuvant therapy (NAT) for patients (pt) with muscle invasive bladder cancer (MIBC) ineligible for cisplatin-based chemotherapy preceding radical cystectomy. Encouraging prospective data indicate PD-1/PD-L1 inhibitors, including pembrolizumab and atezolizumab, are safe and active as NAT for MIBC. Durvalumab (D), a PD-L1 inhibitor, is FDA approved for treating locally advanced or metastatic urothelial carcinoma following platinum-based chemotherapy. The safety and activity of D as NAT in MIBC have not been reported. Methods: We are conducting a single-center sequential multicohort trial (NCT03773666) of D alone (Cohort 1, N=10) and D plus the CD73 inhibitor oleclumab (Cohort 2, N=10) in cT2-T4aN0M0 MIBC pts who are RC candidates and are ineligible for or declined cisplatin-based chemotherapy. The primary endpoint is feasibility, defined as ≥7 of 10 pts receiving at least 1 dose of D followed by radical cystectomy without dose limiting toxicity (DLT) up to 12 wks post-RC. In Cohort 1, D is administered at 750mg IV Q2W for 3 cycles followed by RC 2-4 weeks after the last dose. Baseline and RC tissue and baseline and on-study blood are collected for correlative studies, including immunohistochemistry, genomics, transcriptomics, and metabolomics. Results: Cohort 1 has completed enrollment; ten pts were enrolled between Feb 2019 to Sept 2019. Median age was 67 (Range: 53-85) and 8 (80%) were men. All 10 pts completed 3 durvalumab doses. Eight pts completed planned RC with at least 12wk follow-up post-op to date. No DLTs were observed. One Grade 3 treatment-related adverse event (trAE) was reported (anemia), with no Grade 4 or higher trAE. Pathologic response (

698 Background: Several ICIs are approved for use in first and subsequent lines of therapy in mRCC, either alone or in combination with another ICI or targeted therapy. There is limited data on whether patients who receive an ICI derive benefit from a subsequent line of ICI-based therapy. Methods: We reviewed mRCC patients at our institution who were treated with an ICI between 2009 and 2018 having previously received ICI-based therapy. The primary outcomes of interest were radiologic response and time to treatment failure (TTF) on ICI retreatment. Immune-related adverse events (irAEs) were graded using CTCAE v5.0. Results: A total of 31 patients were retreated with an ICI, either alone (n=15) or in combination with another ICI (n=8), tyrosine kinase inhibitor (n=2) or investigational agent (n=6); reasons for discontinuation of prior ICI were disease progression (n=23), toxicity (n=7) and study completion (n=1). Median age at the start of first-line therapy was 62 years and the majority of patients (n=30, 90%) had International Metastatic RCC Database Consortium intermediate- or poor-risk disease; median follow-up was 3.4 years (95% CI 2.5-4.6). The median number of lines of therapy received prior to ICI retreatment was 3 (range 1-7). Of 27 evaluable patients, 3 (11%) had a partial response (PR) to ICI retreatment (2 with ICI-ICI combination therapy and 1 with single-agent ICI), 13 (48%) had stable disease, and 11 (41%) had progressive disease (PD) as their best response; of the 3 with a PR, 2 had a PR and 1 had SD to prior ICI therapy. In comparison, 13 of 31 patients (42%) had a PR or better to first ICI-based therapy, with 4 (13%) having PD. Median TTF on ICI retreatment was 3.2 months (95% CI 1.8-5.2), compared to 8.2 months (3.3-10.0) on prior ICI. 19 patients experienced an irAE with ICI retreatment, with 8 (26%) suffering a grade 3 or higher irAE. Conclusions: Retreatment with ICIs after prior therapy with an ICI was relatively safe but demonstrated limited efficacy. Additional data, ideally from prospective studies, assessing outcomes of retreating patients with ICIs are needed to determine whether using different ICIs in sequence has a role in treatment of mRCC.

721 Background: Despite therapeutic advancement in Vascular endothelial growth factor receptor (VEGF-R) tyrosine kinase inhibitors (TKIs) and immune checkpoint inhibitors (ICIs) for mRCC treatment, there is currently no reliable predictive biomarkers of response or resistance. Single site biopsies provide limited information given the heterogenous nature of mRCC. Liquid biopsies may overcome these limitations; however, prior CTC capture platforms lacked sufficient sensitivity and specificity to achieve clinically useful detection rates. Methods: Given the prevalence of VEGF dependency, and its reliance on hypoxia, we aimed to increase sensitivity and specificity of capturing and identifying mRCC CTCs using carbonic anhydrase IX (CA IX) and CA XII. In addition, traditional markers for cell capture and identification with epithelial cellular adhesion molecule (EpCAM) and cytokeratin (CK) were included. Exclusion-based Sample Preparation technology was used to maximize cell yield. CD45/34/66b positive blood cells were excluded to ensure high specificity in evaluation of PD-L1 and HLA I expression on CTCs. Results: In a preliminary cohort of 21 mRCC pts (treatment: TKI=12, ICI=5, TKI+ICI=2, baseline=2), we identified heterogeneous populations of CTCs with differential expression of CA XII and CK. We detected CK+ CTCs in 20/21 pts (mean= 5/mL; range 0-53), CAXII+ CTCs in 21/21 pts (mean= 1/mL; range 1-9), and CK+/CAXII+ CTCs in 19/21 pts (mean=7/mL; range 0-102). In pts with multiple CTC samples on treatment, there was a high correlation between the number of CK+ CTCs and treatment response (ROC AUC 0.88). PD-L1 expression in CAXII+ CTCs correlated with response to ICI (ROC AUC 0.77) and TKI (ROC AUC 0.73). HLA I expression in CAXII+ CTCs correlated with response to TKI (ROC AUC 0.73) better than ICI (ROC AUC 0.59). Conclusions: Assessment of CTC heterogeneity may provide valuable molecular insights and diversify tools for early detection of therapeutic response and resistance that may guide treatment decision making. This assay is being tested in ongoing Phase II clinical trials.