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e17539 Background: Chemotherapy with Docetaxel (D) or androgen pathway inhibition (API) with Abiraterone Acetate plus prednisone (AAP), Aplautamide(APA) and Enzalutamide(E) are acceptable, FDA approved treatment options for mCSPC. It is not clear whether the magnitude of benefit varies by the choice of initial agent [chemotherapy vs API] or by volume of disease [High vs Low]. Data is now available from all registration trials by volume status and motivated this analysis to inform initial treatment choice in mCSPC. Methods: We systematically searched MEDLINE(Ovid), Embase, and Scopus for randomized controlled trials of chemotherapy(D) or APIs (AAP, APA, ENZ) that had available hazard ratios (HRs) for overall survival (OS) and Progression Free Survival (PFS) according to patient’s volume of disease. We also reviewed abstracts and presentations from all major conference proceedings. We calculated the pooled overall survival HR and 95% CI by chemotherapy and APIs and by high volume(HVD) and low volume(LVD) using a random effect model, and tested for heterogeneity to assess the null hypothesis that no difference in the survival advantage exists by choice of initial agent and volume of disease. Results: Of 4456 studies identified in our search, there were 8 eligible randomized controlled trials that were included in the analysis. Both D and APIs significantly improved PFS [HR 0.48; 0.45-0.51] and OS [0.72; 0.64-0.81] when added to ADT, however the latter was associated with significantly higher improvement in PFS( P < 0.01) and OS (P = 0.03). In patients treated with D, patients with HVD derive significantly more benefit as compared to LVD( P = 0.046) and patients treated with APIs both HVD and LVD patients derive similar benefit( P = 0.80) (Table). Conclusions: mCSPC patients derive higher magnitude of survival benefit when treated with APIs as compared to D; however, D may be preferred in HVD patients. [Table: see text]

5043 Background: Pathologic complete response (pCR) after NAC for MIBC is strongly correlated with long-term overall survival. However, there are sparse data on the risk of recurrence based on depth of pathologic response (pT0, pTa, pTis, pT1), and the differential impact of clinicopathologic factors and NAC regimen on recurrence. Methods: Baseline data on all pts with cT2-4N0-1 MIBC receiving NAC and who achieved < ypT2N0 disease at radical cystectomy (RC) from 9 international centers were obtained. The key outcome was time to recurrence (TTR) – defined as the time to any recurrence in the urinary tract or regional/distant metastasis, with death (in the absence of recurrence) considered a competing risk. Cox regression analysis was used to analyze the impact of clinical factors on recurrence. Results: A total of 506 pts were available. Median age was 66 years (range 33-86) and 78% (n = 396) were male; median follow-up after RC was 2.6 years. The majority of patients had pure urothelial histology (n = 371, 73%), and baseline stage was cT2N0 (n = 368, 73%), cT3-4N0 (n = 95, 19%) and TanyN1 (n = 43, 9%). NAC regimens were gemcitabine-cisplatin (GC, n = 296, 59%), dose-dense methotrexate-vinblastine-doxorubicin-cisplatin (ddMVAC, n = 141, 28%), split-dose GC (n = 29, 6%), MVAC (n = 29, 6%) and non-cisplatin based regimens (n = 11, 2%). At RC, 304 patients (60%) had ypT0N0 disease, 32 (6%) had ypTaN0, 107 (21%) had ypTisN0 and 63 (13%) had ypT1N0. Overall, 43 patients (8%) recurred with a median TTR of 56 weeks (range 7-251); 5-year freedom from recurrence was 87% (95% CI 83-91). The majority (n = 38) recurred outside the urinary tract. On multivariable analysis, ypTa (HR = 3.36 [1.24-9.11]) and ypT1 (HR = 2.88 [1.33-6.22], p = 0.013) disease at RC were predictors of shorter TTR, while female sex was associated with longer TTR (HR = 0.52 [0.27-0.98], p = 0.043). The type of NAC was not predictive of TTR (GC vs. other, HR = 1.49 [0.75-2.97], p = 0.26). Conclusions: To our knowledge, this is the largest study to quantify the risk of recurrence in pts achieving pathologic response after NAC and RC for MIBC. 8% of patients undergoing NAC and achieving < ypT2N0 at RC recurred. Residual ypTa and ypT1 disease conferred a significantly higher risk of recurrence, while ypTis did not; female sex was associated with a lower risk of recurrence. Importantly, the type of cisplatin-based NAC regimen used was not an independent predictor of recurrence.

5022 Background: Radical cystectomy (RC) is the standard of care for patients with BCG-unresponsive high risk non-muscle invasive bladder cancer (NMIBC), but many patients are unfit for surgery or elect bladder preservation. Based on the reported efficacy of atezolizumab in metastatic urothelial carcinoma and the known expression of PD-L1 in NMIBC after BCG therapy, this trial was designed to evaluate the activity of atezolizumab in BCG-unresponsive high risk NMIBC. Methods: This single arm phase II registration trial testing systemic atezolizumab (1200 mg IV) every 3 weeks for one year aimed to enroll 135 (70 CIS and 65 non-CIS) eligible patients with histologically proven BCG-unresponsive high risk NMIBC who were unfit for or declined RC. Here we report on the subset with CIS (with or without concomitant Ta/T1) among patients who received at least one protocol treatment. The primary endpoint was pathological complete response (CR) rate at 6 months as defined by mandatory biopsy with a null hypothesis of 30% and alternative of 50% with a 1-sided alpha = 0.05 and 96% power. The 3 month CR rate, defined by cytology, cystoscopy and for-cause biopsy, is reported here as a secondary endpoint, in addition to safety. Results: Seventy-five eligible CIS patients were enrolled. Two received no treatment and are not evaluable. Of 73, median patient age was 73.4 years and median number of prior BCG doses was 12. Concomitant Ta/T1 tumor was found in 30 (41.1%) patients, including T1 disease in 16 (21.9%). A CR was observed in 30 (41.1%; 95% CI 29.7%, 53.2%) patients at 3 months and 19 (26.0%; 95% CI 16.5%, 37.6%) at 6 months. Any possibly or probably treatment-related adverse event (AE) was observed in 61 (83.6%) patients. The most frequent AEs were fatigue 36 (49.3%), pruritis 8 (11.0%), hypothyroidism 8 (11.0%), and nausea 8 (11.0%). Grade 3-5 AEs occurred in 9 (12.3%) patients and there was one treatment-related death (myasthenia gravis with respiratory failure and sepsis). Conclusion: The observed response to atezolizumab at 3 and 6 months in patients with BCG-unresponsive CIS was similar to that reported in recent similar trials and meets the benchmark for initial CR defined by the FDA guidance. This trial provided no new safety concerns. The duration of response will determine if this is a suitable treatment option for patients with BCG-unresponsive high risk CIS. Clinical trial information: 02844816 .

5013 Background: Cabozantinib (C), an inhibitor of MET, AXL, and VEGFR, has been shown to promote an immune-permissive environment and has shown promising clinical activity in combination with immune checkpoint inhibitors (ICIs) in solid tumors including renal cell carcinoma and urothelial carcinoma (UC). ICI monotherapy is approved for patients (pts) with locally advanced or metastatic UC with disease progression after platinum-containing chemotherapy. COSMIC-021, a multi-center phase 1b study, is evaluating the combination of C with atezolizumab (A) in various solid tumors (NCT03170960). We report results from Cohort 2 in UC pts with prior platinum-containing chemotherapy. Methods: Eligible pts had ECOG PS 0-1 and had progressed on or after a platinum-containing chemotherapy (including pts with disease recurrences < 12 months after the end of perioperative chemotherapy). Pts received C 40 mg PO QD and A 1200 mg IV Q3W. CT/MRI scans were performed Q6W for first year and Q12W thereafter. The primary endpoint is objective response rate (ORR) per RECIST v1.1 by investigator. Other endpoints include safety, duration of response (DOR), PFS, and OS. Results: As of Dec 20, 2019, 30 pts with advanced UC were enrolled with a median follow-up of 16.5 mo (range 12, 21). Median age was 66 yrs (range 44, 84), 73% were male, and 60% had ECOG PS 1. Primary tumor sites were bladder (80%), renal pelvis (10%), and ureter (10%); the most frequent metastatic sites included lung (40%) and liver (27%). Fourteen pts (47%) had received ≥2 prior systemic anticancer therapies. The most common treatment-related AEs (TRAEs) of any grade were asthenia (37%), diarrhea (27%), decreased appetite (23%), increased transaminases (23%), and mucosal inflammation (20%). Grade 3/4 TRAEs occurred in 57% of pts, with no grade 5 TRAEs. Confirmed ORR per RECIST v1.1 was 27% (8 of 30 pts), including 2 pts with CR. DCR (CR+PR+SD) was 64%. Median DOR was not reached, with the longest DOR ongoing at 14.3+ mos. Median PFS was 5.4 mo (range 0.0+, 17.3+). Conclusions: C in combination with A demonstrated encouraging clinical activity in pts with advanced UC with an acceptable safety profile. Additional cohorts of pts with advanced UC are being explored in the study. Clinical trial information: NCT03170960 .

TPS586 Background: Chemoradiotherapy(CRT) is a SOC for patients with muscle invasive bladder cancer (MIBC) who refuse or are not fit for radical cystectomy. Radiotherapy and chemotherapy are known to increases the PD-L1 expression in bladder cancer. Based on these observations, we hypothesized that addition of atezolizumab to CRT will increase its efficacy. Methods: This is a randomized phase III trial testing CRT with and without atezolizumab for 6 months in 475 patients with MIBC. Pts will be stratified on performance status (0-1 vs. 2); clinical stage (T2 vs T3/T4a, chemotherapy(cisplatin vs 5FU+mitomycin vs gemcitabine); and radiation field (bladder only vs small pelvis). Patients will undergo biopsy 18 week from registration. If they have residual disease they will be taken off protocol treatment and can proceed with alternative SOC option including radical cystectomy. Patients will be followed for 5 years. The primary end point of the study is bladder intact event –free survival (BIEFS). The event is comprised of: recurrence or residual muscle-invasive bladder cancer at 18 weeks or later, clinical evidence of nodal or metastatic disease, radical cystectomy, or death due to any cause. This composite endpoint is reflective of the intent of bladder preservation strategy with radical cystectomy included as one of the outcomes. Secondary end points include overall survival, modified event free survival, pathologic response at 18 weeks, metastasis free survival, cancer specific survival, rate of salvage cystectomy, rate of adverse event and QOL & PRO end points. The expected 3 year BIEFS for the control arm is 52%. The study leadership concluded that a 12% improvement in this endpoint is meaningful for this patient population. With a sample size of 475 patients the study has 85% power to detect the improvement from 52% to 64% in the BIEFS at 3 years (hazard ratio=0.68). The study team will perform translational studies evaluating tumor tissue, whole blood and urine for molecular and immunologic markers of immune response and response to RT. Successful completion of this trial could lead to a new treatment paradigm for patients with muscle invasive bladder cancer. Clinical trial information: NCT03775265.

205 Background: Metastatic prostate cancer (mPC) is treated with androgen deprivation therapy( ADT). Duration of response to ADT predicts patient’s survival. It has been shown in observational studies that concurrent statin use may prolong response to ADT. Studies in mice have shown negative interactions. We wanted to examine the effect of this interaction in patients being followed at Mayo Clinic Arizona (MCA). Methods: We examined 441 patients with mPC, who received ADT and were treated at MCA from year 2011 to 2017. . Our study evaluated the time to progression (TTP) and overall survival(OS) for patients with mPC on ADT with or without concurrent statin use. Among the patients who were evaluated, there was a subset of 156 patients taking abiraterone (ABI). Characteristics were compared between statin users and nonusers using Chi squared test and Wilcoxon rank-sum tests. The primary outcome was TTP defined as the duration from ADT initiation to disease progression. The association between statin use and TTP was analyzed by multivariable Cox regression to estimate hazard ratios (HRs) and 95% Conference Interval (CI), and adjusted for Gleason score, primary therapy type, prior ADT, metastatic status, and PSA at ADT initiation. Results: There was no significant difference in TTP when comparing patients with statin to those without a statin. The HR for statin use vs no statin use is 1.049 with CI (0.838, 1.314) and p-value is 0.677. There was no significant difference in overall survival when comparing statin vs no statin use. The HR for statin use vs no statin use was 0.928(CI 0.642, 1.342) with p-value at 0.693. In the ABI population, there was no significant difference in TTP for patients with statin vs no statin. HR was 1.00 CI (0.725, 1.377) with p-value at 0.998. For overall survival, there was no significant difference with HR at 0.852 (CI 0.502, 1.446) with p-value at 0.553. Conclusions: Despite retrospective studies showing benefit of use of statin in men with prostate cancer, our study observed no difference in long term outcomes. Possible explanations could be smaller sample size, inability to verify data as medication intake was not verified directly. Also, patient’s compliance with medications could be a confounding variable.

AbstractBackgroundProstate‐specific membrane antigen (PSMA) is a well‐established therapeutic and diagnostic target overexpressed in both primary and metastatic prostate cancers. PSMA antibody‐drug conjugate (PSMA ADC) is a fully human immunoglobulin G1 anti‐PSMA monoclonal antibody conjugated to monomethylauristatin E, which binds to PSMA‐positive cells and induces cytotoxicity. In a phase 1 study, PSMA ADC was well tolerated and demonstrated activity as measured by reductions in serum prostate‐specific antigen (PSA) and circulating tumor cells (CTCs). To further assess PSMA ADC, we conducted a phase 2 trial in metastatic castration‐resistant prostate cancer (mCRPC) subjects who progressed following abiraterone/enzalutamide (abi/enz) therapy.MethodsA total of 119 (84 chemotherapy‐experienced and 35 chemotherapy‐naïve) subjects were administered PSMA ADC 2.5 or 2.3 mg/kg IV q3w for up to eight cycles. Antitumor activity (best percentage declines in PSA and CTCs from baseline and tumor responses through radiological imaging), exploratory biomarkers, and safety (monitoring of adverse events [AEs], clinical laboratory tests, and Eastern Cooperative Oncology Group performance status) were assessed.ResultsPSA declines ≥50% occurred in 14% of all treated (n = 113) and 21% of chemotherapy‐naïve subjects (n = 34). CTC declines ≥50% were seen in 78% of all treated (n = 77; number of subjects with ≥5 CTCs at baseline and a posttreatment result) and 89% of chemotherapy‐naïve subjects (n = 19); 47% of all treated and 53% of chemotherapy‐naïve subjects had a transition from ≥5 to less than 5 CTCs/7.5 mL blood at some point during the study. PSA and CTC reductions were associated with high PSMA expression (CTCs or tumor tissue) and low neuroendocrine serum markers. In the chemotherapy‐experienced group, the best overall radiologic response to PSMA ADC treatment was stable disease in 51 (60.7%) subjects; 5.7% of subjects in the chemotherapy‐naïve group had partial responses. The most common treatment‐related AEs ≥Common Terminology Criteria for AE (CTCAE) grade 3 were neutropenia, fatigue, electrolyte imbalance, anemia, and neuropathy. The most common serious AEs were dehydration, hyponatremia, febrile neutropenia, and constipation. Two subjects who received 2.5 mg/kg died of sepsis.ConclusionsPSMA ADC demonstrated some activity with respect to PSA declines, CTC conversions/reductions, and radiologic assessments in abi/enz treated mCRPC subjects. Clinically significant treatment‐related AEs included neutropenia and neuropathy.

5063 Background: The systemic therapies available to patients with metastatic prostate cancer (mPC) have improved dramatically over the past decade. Prior to 2010, the only agents with a proven survival benefit for patients with metastatic disease were androgen deprivation therapy and docetaxel. Since then, five new agents have been FDA approved and have proven survival benefit in phase III trials. Anecdotal experience suggests that the increased available lines of therapy have changed the profile of mPC to include a higher prevalence of visceral metastases. Methods: A retrospective review of 474 patients with prostate cancer who died in 2009 and in 2016 was performed. Patients with metastatic disease who had imaging within 6 months of death were included. A total of 164 patients were eligible for analysis. Results: Mean age at death overall was 77.4 years (SD 9.5) and did not differ signifiantly by cohort. Overall rates of visceral and distant metastases to include lung, liver, adrenal, brain, renal, spleen, and thyroid, were higher in patients who died in 2016 as compared to those who died in 2009 (40.0% and 26.1%, respectively, p = 0.07). Lung metastases were more prevalent in patients who died in 2016 versus in 2009 at 26.3% and 13.0%, respectively (p = 0.05). Patients who died in 2009 received a median of 3 (range 1-10) systemic treatments versus 4 (range 0-13) in those who died in 2016 (p = 0.005). Forty-four percent of patients who died in 2016 used five or more lines of systemic treatments compared to 26.1% of patients in 2009. Conclusions: The emergence of new systemic therapies for mPC is changing the natural history of the disease. Forty percent of patients now develop visceral metastases compared to 26% in the past. These changes will drive the need for new treatment approaches targeting visceral metastases. [Table: see text]

536 Background: The management of malignant mesothelioma of the tunica vaginalis of the testes (MMTVT) is not clearly defined, though retroperitoneal lymph node dissection has been reported as a diagnostic and potentially therapeutic option. Herein we present our experience with robot assisted retroperitoneal lymph node dissection (RARPLND) in a series of patients with MMTVT. Methods: The Mayo Clinic cancer registry was queried from 1972-present for all patients who had a diagnosis of MMTVT. Six patients were identified, five of whom were treated with RPLND, where four underwent RARPLND. Data was collected on pertinent demographic, preoperative, perioperative, postoperative outcomes and follow-up oncological data. Results: In five patients who underwent RPLND, the median age was 50 years (IQR 34-51), median BMI was 26.9 (IQR 26.4-30.6). Four patients originally presented with right sided symptomatic hydroceles, while one presented with right sided chronic epididymitis. Orchiectomy (one simple, two inguinal radical) was performed in three patients and hydrocelectomy in the other two patients prior to presentation. Preoperative cross-sectional imaging, including PET-CT scan in three patients, was negative for lymphadenopathy or metastasis. RARPLND was performed in 4/5 (80%) cases and concomitant hemiscrotectomy in 4/5 (80%) cases. Full bilateral template was performed in three patients and right modified template was performed in the remaining two. Median lymph node yield was 29 (IQR 22-32) and median blood loss was 275 cc (IQR 200-300). Positive retroperitoneal lymph nodes were found in 3/5 (60%) cases. Final margins of hemiscrotectomy were negative in all four cases. All patients who underwent RARPLND were discharged home on postoperative day one. One patient received four cycles of adjuvant Cisplatin and Pemetrexed. Mean follow-up was 27 months (range 2-47). No patients recurred. Conclusions: MMTVT is a very rare malignancy with high potential for retroperitoneal lymph node dissemination. Regardless of the approach, RPLND may provide both a diagnostic and therapeutic benefit, with the robotic approach affording a potentially expedited recovery.

TPS4591 Background: Radical cystectomy is the standard of care for patients with BCG-unresponsive high risk non-muscle invasive bladder cancer (NMIBC). Based on the reported efficacy of atezolizumab in metastatic urothelial carcinoma and the known expression of PD-L1 expression in NMIBC after BCG therapy, this trial will evaluate the activity of atezolizumab in BCG-unresponsive high risk NMIBC. Methods: This is a single arm phase II trial testing systemic atezolizumab (1200 mg IV) every 3 weeks for one year in 135 patients with BCG-unresponsive high risk NMIBC. The study will enroll 70 patients with CIS (with or without concomitant Ta/T1) and 65 with Ta/T1 only. Patients with CIS at baseline will undergo mandatory repeat biopsy at 6 months, and all other patients only for suspected recurrence. Patients with persistent CIS, high grade Ta/T1 recurrence or progression to muscle invasive or metastatic disease will be taken off treatment. The co-primary endpoints are: (1) complete response (CR) at 6 months in the CIS subgroup, and (2) event-free survival (EFS) at 18 months in the overall population. A hierarchical approach will be used to test the two co-primary endpoints. Secondary endpoints include duration of CR as well as progression-free, cystectomy-free, bladder cancer-specific and overall survival in all patients. Response will be correlated to expression of PD-L1 and CD8 by IHC, and to molecular subtypes and immune signatures by RNA-sequencing. Results: If ≥28 (40%) CIS patients respond, the agent will be considered promising. This design has a significance level of 4.6%, and a power of 96%. If the lower bound of the 90% confidence interval of the 18-month EFS excludes 20%, the investigators will conclude the regimen significantly improves EFS relative to historical data (type I error rate 0.05 and statistical power 0.93). Conclusion:Successful completion of this trial could lead to a new treatment paradigm for patients with BCG-unresponsive high risk NMIBC. Funding: NIH/NCI grants: CA180888, CA180819, CA180820, CA180821, and CA180863. Clinical trial information: NCT02844816.