Purpose Germline mutations in DNA damage repair (DDR) genes are identified in a significant proportion of patients with metastatic prostate cancer, but the clinical implications of these genes remain unclear. This prospective multicenter cohort study evaluated the prevalence and effect of germline DDR (gDDR) mutations on metastatic castration-resistance prostate cancer (mCRPC) outcomes. Patients and Methods Unselected patients were enrolled at diagnosis of mCRPC and were screened for gDDR mutations in 107 genes. The primary aim was to assess the impact of ATM/BRCA1/BRCA2/ PALB2 germline mutations on cause-specific survival (CSS) from diagnosis of mCRPC. Secondary aims included the association of gDDR subgroups with response outcomes for mCRPC treatments. Combined progression-free survival from the first systemic therapy (PFS) until progression on the second systemic therapy (PFS2) was also explored. Results We identified 68 carriers (16.2%) of 419 eligible patients, including 14 with BRCA2, eight with ATM, four with BRCA1, and none with PALB2 mutations. The study did not reach its primary end point, because the difference in CSS between ATM/BRCA1/BRCA2/PALB2 carriers and noncarriers was not statistically significant (23.3 v 33.2 months; P = .264). CSS was halved in germline BRCA2 (g BRCA2) carriers (17.4 v 33.2 months; P = .027), and g BRCA2 mutations were identified as an independent prognostic factor for CCS (hazard ratio [HR], 2.11; P = .033). Significant interactions between g BRCA2 status and treatment type (androgen signaling inhibitor v taxane therapy) were observed (CSS adjusted P = .014; PFS2 adjusted P = .005). CSS (24.0 v 17.0 months) and PFS2 (18.9 v 8.6 months) were greater in g BRCA2 carriers treated in first line with abiraterone or enzalutamide compared with taxanes. Clinical outcomes did not differ by treatment type in noncarriers. Conclusion g BRCA2 mutations have a deleterious impact on mCRPC outcomes that may be affected by the first line of treatment used. Determination of g BRCA2 status may be of assistance for the selection of the initial treatment in mCRPC. Nonetheless, confirmatory studies are required before these results can support a change in clinical practice.

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487 Background: The phase 3 JAVELIN Bladder 100 trial (NCT02603432) showed significantly longer overall survival (OS) with avelumab + best supportive care (BSC) vs BSC alone in patients (pts) with advanced UC that had not progressed with 1L platinum-containing chemotherapy. Avelumab 1L maintenance is now considered standard of care in treatment guidelines. We report trial data with ≥2-years follow-up in all pts (additional 19 months from the initial analysis). Methods: Pts with unresectable locally advanced or metastatic UC without disease progression with 4-6 cycles of 1L gemcitabine + cisplatin or carboplatin were randomized 1:1 to receive avelumab + BSC or BSC alone. The primary endpoint was OS, assessed from randomization in all pts and in pts with PD-L1+ tumors (Ventana SP263 assay). Secondary endpoints included progression-free survival (PFS) and safety. Results: 700 pts were randomized (350 per arm); 358 (51.1%) had PD-L1+ tumors. With extended follow-up (median, ≥38 months in both arms for all pts; data cutoff, June 4, 2021), OS remained significantly longer in the avelumab + BSC vs BSC alone arm in all randomized pts and in pts with PD-L1+ tumors (Table). An OS benefit was observed across prespecified subgroups. PFS (by investigator) was longer with avelumab + BSC vs BSC alone in all randomized pts and in pts with PD-L1+ tumors (Table). In the avelumab + BSC and BSC alone arms, respectively, 185 (52.9%) vs 252 (72.0%) pts received a subsequent anticancer drug therapy, including a PD-(L)1 inhibitor in 40 (11.4%) vs 186 (53.1%) pts. Long-term safety was consistent with previous avelumab monotherapy studies, with no new safety signals. Conclusions: Long-term follow-up from the JAVELIN Bladder 100 trial continues to show prolonged OS with avelumab + BSC vs BSC alone. These results further support the standard-of-care role for avelumab as 1L maintenance in pts with advanced UC that has not progressed with 1L platinum-containing chemotherapy. Clinical trial information: NCT02603432. [Table: see text]

545 Background: Metastatic papillary renal cancer (PRC) has poor outcomes and there is need for new treatments. There is a strong rationale for investigating MET and PD-L1 inhibition in this disease. In this study, we investigate savolitinib (MET inhibitor) and durvalumab (PD-L1 inhibitor) together. Methods: This single arm phase I/II trial explored durvalumab and savolitinib at starting doses of 1500mg Q4W and 600mg OD respectively, with a 4wk savolitinib run-in. Treatment naïve or previously treated patients with metastatic PRC were included. Response rate (RR) (RECIST v1.1) was the primary endpoint. Progression free survival (PFS), tolerability (CTCAE v4) and overall survival were secondary endpoints. Biomarkers were explored from archived tissue. Results: Dose escalation work identified a dose of durvalumab of 1500mg Q4W and savolitinib 600mg OD to take forward to phase II. Between Jan 2017 and Jul 2018, 42 patients were enrolled at this dose. 1 patient did not receive study treatment. The following analyses were performed on the remaining 41 patients. 12% of patients did not receive the combination (3 PD, 1 death, 1 PS deterioration). The median follow up was 8.9 months (95% CI: 6.9-10.9 months). IMDC good, intermediate and poor risk disease occurred in 29% (n=12), 63% (n=26), and 7% (n=3) patients respectively. Overall RR was 27% (11/41), while median PFS was 3.3 months (95% CI: 1.5-NR months). RR and median PFS in the previously untreated cohort (N=28) were 29% (8/28) and 12.0 months (95% CI: 1.5-NR months) respectively. Grade 3/4 toxicity occurred in 15 patients. Discontinuation for toxicity occurred in 3 patients, all due to liver toxicities. Biomarker work including PD-L1 and MET expression will be included in the analysis. Conclusions: The combination of savolitinib and durvalumab appears safe and associated with clinical activity in PRC. Clinical trial information: NCT02819596.

Our results validate the IMDC model for first-line pazopanib in mRCC and confirm the effectiveness and safety of this treatment.