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PURPOSE Orteronel (TAK-700) is a nonsteroidal 17,20-lyase inhibitor suppressing androgen synthesis. We evaluated the clinical benefit of orteronel when added to androgen deprivation therapy (ADT) in patients with newly diagnosed metastatic hormone-sensitive prostate cancer. METHODS In this open-label randomized phase III study, patients with metastatic hormone-sensitive prostate cancer were randomly assigned 1:1 to ADT with orteronel (300 mg oral twice daily; experimental arm) or ADT with bicalutamide (50 mg oral once daily; control arm). The primary objective was the comparison of overall survival (OS), targeting a 33% improvement in median survival. A stratified log-rank test with a one-sided P ≤ .022 would indicate statistical significance. Secondary end points were progression-free survival (PFS), prostate-specific antigen (PSA) level at 7 months (≤ 0.2 v 0.2 to ≤ 4 v > 4 ng/mL), and adverse event profile. RESULTS Among 1,279 patients included in the analysis, 638 were randomly assigned to the ADT plus orteronel arm and 641 to the control arm. The median age was 68 years; 49% had extensive disease. After a median follow-up of 4.9 years, there was a significant improvement in PFS (median 47.6 v 23.0 months, hazard ratio 0.58; 95% CI, 0.51 to 0.67; P < .0001) and PSA response at 7 months ( P < .0001), but not in OS (median 81.1 v 70.2 months, hazard ratio 0.86; 95% CI, 0.72 to 1.02; P = .040, one-sided). More grade 3/4 adverse events occurred in the experimental versus the control arms (43% v 14%). Postprotocol life-prolonging therapy was received by 77.4% of patients in the control arm and 61.3% of patients in the orteronel arm. CONCLUSION The study did not meet the primary end point of improved OS with orteronel. The lack of correlation of PFS and PSA response with OS raises concerns over assumption of their consistent surrogacy for OS in the context of extensive postprotocol therapy in this setting.

Supplementary Figure Legend

COXEN Model development

Purpose:Immune checkpoint blockade has improved outcomes across tumor types; little is known about the efficacy of these agents in rare tumors. We report the results of the (nonpancreatic) neuroendocrine neoplasm cohort of SWOG S1609 dual anti–CTLA-4 and anti–PD-1 blockade in rare tumors (DART).Patients and Methods:We performed a prospective, open-label, multicenter phase II clinical trial of ipilimumab plus nivolumab across multiple rare tumor cohorts, with the (nonpancreatic) neuroendocrine cohort reported here. Response assessment by grade was not prespecified. The primary endpoint was overall response rate [ORR; RECIST v1.1; complete response (CR) and partial response (PR)]; secondary endpoints included progression-free survival (PFS), overall survival (OS), stable disease >6 months, and toxicity.Results:Thirty-two eligible patients received therapy; 18 (56%) had high-grade disease. Most common primary sites were gastrointestinal (47%; N = 15) and lung (19%; N = 6). The overall ORR was 25% [95% confidence interval (CI) 13–64%; CR, 3%, N = 1; PR, 22%, N = 7]. Patients with high-grade neuroendocrine carcinoma had an ORR of 44% (8/18 patients) versus 0% in low/intermediate grade tumors (0/14 patients; P = 0.004). The 6-month PFS was 31% (95% CI, 19%–52%); median OS was 11 months (95% CI, 6–∞). The most common toxicities were hypothyroidism (31%), fatigue (28%), and nausea (28%), with alanine aminotransferase elevation (9%) as the most common grade 3/4 immune-related adverse event, and no grade 5 events.Conclusions:Ipilimumab plus nivolumab demonstrated a 44% ORR in patients with nonpancreatic high-grade neuroendocrine carcinoma, with 0% ORR in low/intermediate grade disease.

Supplemental Figure 1: CONSORT Diagram

Supplemental Table 1. Calculation of individual drug scores for COXEN

Supplemental Table 2. Comparing GC and DDMVAC for Pathologic Response at Cystectomy - intention to treat analysis

Appendix

Supplemental Table 1: Clinical and tumor characteristics of long-term responders

Purpose:Metaplastic breast cancer (MpBC) is a rare aggressive subtype that responds poorly to cytotoxics. Median survival is approximately 8 months for metastatic disease. We report results for advanced MpBC treated with ipilimumab + nivolumab, a cohort of S1609 for rare cancers (DART: NCT02834013).Patients and Methods:Prospective, open-label, multicenter phase II (two-stage) trial of ipilimumab (1 mg/kg i.v. every 6 weeks) plus nivolumab (240 mg i.v. every 2 weeks) for advanced MpBC. Primary endpoint was objective response rate (ORR). Secondary endpoints included progression-free survival (PFS), overall survival (OS), and toxicity.Results:Overall, 17 evaluable patients enrolled. Median age was 60 years (26–85); median number of prior therapy lines was 2 (0–5). ORR was 18%; 3 of 17 patients achieved objective responses (1 complete, 2 partial responses; 2 spindle cell, 1 chondromyxoid histology), which are ongoing at 28+, 33+, and 34+ months, respectively. Median PFS and OS were 2 and 12 months, respectively. Altogether, 11 patients (65%) experienced adverse events (AE), including one grade 5 AE. Eight patients (47%) developed an immune-related AE (irAE), with adrenal insufficiency observed in all 3 responders. Responses occurred in tumors with low tumor mutational burden, low PD-L1, and absent tumor-infiltrating lymphocytes.Conclusions:The ipilimumab and nivolumab combination showed no new safety signals and met its primary endpoint with 18% ORR in advanced, chemotherapy-refractory MpBC. All responses are ongoing at >2 to almost 3 years later. The effect of ipilimumab and nivolumab was associated with exceptional responses in a subset of patients versus no activity. This combination warrants further investigation in MpBC, with special attention to understanding mechanism of action, and carefully designed to weigh against the significant risks of irAEs.

Purpose:Dose-dense methotrexate-vinblastine-adriamycin-cisplatin (ddMVAC) and gemcitabine-cisplatin (GC) are accepted neoadjuvant regimens for muscle-invasive bladder cancer. The aim of this study was to validate the score from a coexpression extrapolation (COXEN) algorithm–generated gene expression model (GEM) as a biomarker in patients undergoing radical cystectomy.Patients and Methods:Eligibility included cT2-T4a N0 M0, urothelial bladder cancer, ≥ 5 mm of viable tumor, cisplatin eligible, with plan for cystectomy; 237 patients were randomized between ddMVAC, given every 14 days for four cycles, and GC, given every 21 days for four cycles. The primary objective assessed prespecified dichotomous treatment-specific COXEN score as predictive of pT0 rate or ≤ pT1 (downstaging) at surgery.Results:Among 167 evaluable patients, the OR for pT0 with the GC GEM score in GC-treated patients was 2.63 [P = 0.10; 95% confidence interval (CI), 0.82–8.36]; for the ddMVAC COXEN GEM score with ddMVAC treatment, the OR was 1.12 (P = 0.82, 95% CI, 0.42–2.95). The GC GEM score was applied to pooled arms (GC and ddMVAC) for downstaging with an OR of 2.33 (P = 0.02; 95% CI, 1.11–4.89). In an intention-to-treat analysis of eligible patients (n = 227), pT0 rates for ddMVAC and GC were 28% and 30% (P = 0.75); downstaging was 47% and 40% (P = 0.27), respectively.Conclusions:Treatment-specific COXEN scores were not significantly predictive for response to individual chemotherapy treatment. The COXEN GEM GC score was significantly associated with downstaging in the pooled arms. Additional biomarker development is planned.

Supplemental Table 3 Number of Patients with a Given Type and Grade of Adverse Event Adverse Events Unlikely or Not Related to Treatment Excluded

Purpose: Dose-dense methotrexate-vinblastine-adriamycin-cisplatin (ddMVAC) and gemcitabine-cisplatin (GC) are accepted neoadjuvant regimens for muscle-invasive bladder cancer. The aim of this study was to validate the score from a coexpression extrapolation (COXEN) algorithm–generated gene expression model (GEM) as a biomarker in patients undergoing radical cystectomy. Patients and Methods: Eligibility included cT2-T4a N0 M0, urothelial bladder cancer, ≥ 5 mm of viable tumor, cisplatin eligible, with plan for cystectomy; 237 patients were randomized between ddMVAC, given every 14 days for four cycles, and GC, given every 21 days for four cycles. The primary objective assessed prespecified dichotomous treatment-specific COXEN score as predictive of pT0 rate or ≤ pT1 (downstaging) at surgery. Results: Among 167 evaluable patients, the OR for pT0 with the GC GEM score in GC-treated patients was 2.63 [P = 0.10; 95% confidence interval (CI), 0.82–8.36]; for the ddMVAC COXEN GEM score with ddMVAC treatment, the OR was 1.12 (P = 0.82, 95% CI, 0.42–2.95). The GC GEM score was applied to pooled arms (GC and ddMVAC) for downstaging with an OR of 2.33 (P = 0.02; 95% CI, 1.11–4.89). In an intention-to-treat analysis of eligible patients (n = 227), pT0 rates for ddMVAC and GC were 28% and 30% (P = 0.75); downstaging was 47% and 40% (P = 0.27), respectively. Conclusions: Treatment-specific COXEN scores were not significantly predictive for response to individual chemotherapy treatment. The COXEN GEM GC score was significantly associated with downstaging in the pooled arms. Additional biomarker development is planned.

Purpose: Immune checkpoint blockade has improved outcomes across tumor types; little is known about the efficacy of these agents in rare tumors. We report the results of the (nonpancreatic) neuroendocrine neoplasm cohort of SWOG S1609 dual anti–CTLA-4 and anti–PD-1 blockade in rare tumors (DART). Patients and Methods: We performed a prospective, open-label, multicenter phase II clinical trial of ipilimumab plus nivolumab across multiple rare tumor cohorts, with the (nonpancreatic) neuroendocrine cohort reported here. Response assessment by grade was not prespecified. The primary endpoint was overall response rate [ORR; RECIST v1.1; complete response (CR) and partial response (PR)]; secondary endpoints included progression-free survival (PFS), overall survival (OS), stable disease >6 months, and toxicity. Results: Thirty-two eligible patients received therapy; 18 (56%) had high-grade disease. Most common primary sites were gastrointestinal (47%; N = 15) and lung (19%; N = 6). The overall ORR was 25% [95% confidence interval (CI) 13–64%; CR, 3%, N = 1; PR, 22%, N = 7]. Patients with high-grade neuroendocrine carcinoma had an ORR of 44% (8/18 patients) versus 0% in low/intermediate grade tumors (0/14 patients; P = 0.004). The 6-month PFS was 31% (95% CI, 19%–52%); median OS was 11 months (95% CI, 6–∞). The most common toxicities were hypothyroidism (31%), fatigue (28%), and nausea (28%), with alanine aminotransferase elevation (9%) as the most common grade 3/4 immune-related adverse event, and no grade 5 events. Conclusions: Ipilimumab plus nivolumab demonstrated a 44% ORR in patients with nonpancreatic high-grade neuroendocrine carcinoma, with 0% ORR in low/intermediate grade disease.

TPS581 Background: UC is 2nd most common genitourinary cancer. Current SOC offers platinum-based (PB) first line chemotherapy (chemo) with ddMVAC or gemcitabine-cisplatin (GC) regimens. For cisplatin ineligible patients (pts), SOC includes gemcitabine-carboplatin (GCa), and in select pts pembrolizumab. Erdafitinib is approved for pts with FGFR alterations and Enfortumab vedotin (EV) is approved for previously treated pts. A phase I/II CTEP study of eribulin (E) for metastatic UC (mUC) established the activity of E in UC with objective response rate (ORR) of 37.5% and a median progression free survival (PFS) of 4.1 months (mo) and median overall survival (OS) of 9.5 mo (N=150). A phase II CTEP study of gemcitabine-eribulin (GE) in cisplatin ineligible mUC showed an ORR of 50%, median OS of 11.9 mo and median PFS of 5.3 mo (N=24). The most common Grade 3-4 toxicities included: neutropenia 63%, anemia and fatigue 29%. Pts with liver metastases benefited from therapy with 5 responders in 7 pts for GE vs 12 out 49 E. Methods: This is a phase III, randomized 3 arm study comparing E vs. GE vs. SOC (docetaxel, paclitaxel, or gemcitabine). E is given at 1.4mg/m2 on day (D) 1 and 8 of a 21 D cycle. In the GE arm, gemcitabine is added to E at 1000 mg/m2 dose to D1 and D8. SOC follows standard dosing of the agents. There is no limit to the number/sequence of prior regimens. A simplified summary of eligibility criteria is presented here. All pts must have: received frontline systemic treatment such as PB chemo or a non-platinum regimen; received PD1/PDL1 Ab or be deemed ineligible for PD1/PDL1 Ab; received EV. Assuming a median OS for the SOC arm of 7 mo the study seeks to find at least a 50% increase in median OS to 10.5 mo (Hazard Ratio (HR) = 0.667). One-sided 0.0125 type I error to account for testing of two primary hypotheses (Each arm vs. SOC). 87% power to detect a 3.5 mo improvement in OS. We require 140 eligible (155 total) pts in each arm for a total of 465. The study was activated in Feb 2021 and accrual is ongoing. Funding: National Institutes of Health/National Cancer Institute grants U10CA180888, U10CA180819. Clinical trial information: NCT04579224 .

Purpose: Metaplastic breast cancer (MpBC) is a rare aggressive subtype that responds poorly to cytotoxics. Median survival is approximately 8 months for metastatic disease. We report results for advanced MpBC treated with ipilimumab + nivolumab, a cohort of S1609 for rare cancers (DART: NCT02834013). Patients and Methods: Prospective, open-label, multicenter phase II (two-stage) trial of ipilimumab (1 mg/kg i.v. every 6 weeks) plus nivolumab (240 mg i.v. every 2 weeks) for advanced MpBC. Primary endpoint was objective response rate (ORR). Secondary endpoints included progression-free survival (PFS), overall survival (OS), and toxicity. Results: Overall, 17 evaluable patients enrolled. Median age was 60 years (26–85); median number of prior therapy lines was 2 (0–5). ORR was 18%; 3 of 17 patients achieved objective responses (1 complete, 2 partial responses; 2 spindle cell, 1 chondromyxoid histology), which are ongoing at 28+, 33+, and 34+ months, respectively. Median PFS and OS were 2 and 12 months, respectively. Altogether, 11 patients (65%) experienced adverse events (AE), including one grade 5 AE. Eight patients (47%) developed an immune-related AE (irAE), with adrenal insufficiency observed in all 3 responders. Responses occurred in tumors with low tumor mutational burden, low PD-L1, and absent tumor-infiltrating lymphocytes. Conclusions: The ipilimumab and nivolumab combination showed no new safety signals and met its primary endpoint with 18% ORR in advanced, chemotherapy-refractory MpBC. All responses are ongoing at >2 to almost 3 years later. The effect of ipilimumab and nivolumab was associated with exceptional responses in a subset of patients versus no activity. This combination warrants further investigation in MpBC, with special attention to understanding mechanism of action, and carefully designed to weigh against the significant risks of irAEs.

Background The authors previously reported the results of the nonpancreatic neuroendocrine neoplasm cohort of the SWOG S1609 DART (Dual Anti-CTLA-4 and Anti-PD-1 Blockade in Rare Tumors) trial, which permitted all histologic grades and had a 44% overall response rate (ORR) among patients with high-grade disease. Here they sought to validate their findings in a dedicated prospective cohort of high-grade neuroendocrine neoplasms within S1609. Methods A prospective, open-label, multicenter, phase 2 clinical trial of ipilimumab plus nivolumab was conducted across multiple rare tumor cohorts. The dedicated, high-grade neuroendocrine neoplasm cohort was examined here. The primary end point was the ORR according to version 1.1 of the Response Evaluation Criteria in Solid Tumors. Secondary end points included progression-free survival (PFS), overall survival (OS), and toxicity. Results Nineteen patients with high-grade neuroendocrine neoplasms (defined by local pathology review) were enrolled in this cohort of S1609. The most common primary sites were unknown primaries (21%), which were followed by the rectum, gastroesophageal junction, cervix, and pancreas (11%). The median number of lines of prior therapy was 1 (range, 0-3). All patients were microsatellite-stable. The median Ki-67 value was 80%. The ORR was 26% (95% confidence interval [CI], 11%-45%), and the clinical benefit rate (stable disease for ≥6 months plus partial responses plus complete responses) was 32% (95% CI, 13%-57%). The 6-month PFS rate was 32% (95% CI, 16%-61%) with a median PFS of 2.0 months (95% CI, 1.8 months to ∞) and a median OS of 8.7 months (95% CI, 6.1 months to ∞). The most common toxicities were fatigue (32%) and rash (26%), and the most common grade 3/4 immune-related adverse event was rash (15%); there were no events that required treatment discontinuation and no grade 5 events. Conclusions Ipilimumab plus nivolumab demonstrated a 26% ORR in patients with high-grade neuroendocrine neoplasms, with durable responses seen in patients with refractory disease.

Summary Background MET (also known as hepatocyte growth factor receptor) signalling is a key driver of papillary renal cell carcinoma (PRCC). Given that no optimal therapy for metastatic PRCC exists, we aimed to compare an existing standard of care, sunitinib, with the MET kinase inhibitors cabozantinib, crizotinib, and savolitinib for treatment of patients with PRCC. Methods We did a randomised, open-label, phase 2 trial done in 65 centres in the USA and Canada. Eligible patients were aged 18 years or older with metastatic PRCC who had received up to one previous therapy (excluding vascular endothelial growth factor-directed and MET-directed agents). Patients were randomly assigned to receive sunitinib, cabozantinib, crizotinib, or savolitinib, with stratification by receipt of previous therapy and PRCC subtype. All drug doses were administered orally: sunitinib 50 mg, 4 weeks on and 2 weeks off (dose reductions to 37·5 mg and 25 mg allowed); cabozantinib 60 mg daily (reductions to 40 mg and 20 mg allowed); crizotinib 250 mg twice daily (reductions to 200 mg twice daily and 250 mg once daily allowed); and savolitinib 600 mg daily (reductions to 400 mg and 200 mg allowed). Progression-free survival (PFS) was the primary endpoint. Analyses were done in an intention-to-treat population, with patients who did not receive protocol therapy excluded from safety analyses. This trial is registered with ClinicalTrials.gov, NCT02761057. Findings Between April 5, 2016, and Dec 15, 2019, 152 patients were randomly assigned to one of four study groups. Five patients were identified as ineligible post-randomisation and were excluded from these analyses, resulting in 147 eligible patients. Assignment to the savolitinib (29 patients) and crizotinib (28 patients) groups was halted after a prespecified futility analysis; planned accrual was completed for both sunitinib (46 patients) and cabozantinib (44 patients) groups. PFS was longer in patients in the cabozantinib group (median 9·0 months, 95% CI 6–12) than in the sunitinib group (5·6 months, 3–7; hazard ratio for progression or death 0·60, 0·37–0·97, one-sided p=0·019). Response rate for cabozantinib was 23% versus 4% for sunitinib (two-sided p=0·010). Savolitinib and crizotinib did not improve PFS compared with sunitinib. Grade 3 or 4 adverse events occurred in 31 (69%) of 45 patients receiving sunitinib, 32 (74%) of 43 receiving cabozantinib, ten (37%) of 27 receiving crizotinib, and 11 (39%) of 28 receiving savolitinib; one grade 5 thromboembolic event was recorded in the cabozantinib group. Interpretation Cabozantinib treatment resulted in significantly longer PFS compared with sunitinib in patients with metastatic PRCC. Funding National Institutes of Health and National Cancer Institute.

Background Checkpoint inhibitors acting against PD-1 and CTLA-4 have provided significant benefit for patients. However, their efficacy in rare tumors has not been determined. This abstract presents the results of combination therapy with anti-CTLA and anti-PD-1 in the thyroid cohort of SWOG S1609 Dual Anti-CTLA-4 & Anti-PD-1 blockade in Rare Tumors (DART). Methods This study is a prospective, open-label, multicenter phase 2 clinical trial of ipilimumab (1 mg/kg intravenously every 6 weeks) plus nivolumab (240 mg intravenously every 2 weeks) in rare tumors. Here we report the outcomes from thyroid cancer patients. The primary endpoint is objective response rate (ORR) (RECIST v1.1) (confirmed complete response (CR) and partial responses (PR)); progression-free survival (PFS), overall survival (OS), stable disease (SD) >6 months, and toxicity are secondary endpoints. Results Twenty-one patients were registered and seventeen were eligible and received therapy. Median age of the patients was 59 (range 33–78), 59% (N=10) of enrolled patients were male. The most common subtype of thyroid cancer was papillary (47%, N=8), then medullary (24%, N=4), anaplastic (24%, N=4) and Hurtle cell histology (6%, N=1). The ORR was 12% [CR, 0%, N= 0; PR, 12%, N= 2; 1 papillary and 1 anaplastic subtype]; in addition 12% (N=2) had unconfirmed PR (both papillary subtype). Of note, 1 out of 4 patients with anaplastic thyroid carcinoma (25%) had a response that lasted more than two years. 35% (N=6) of patients had SD for over 6 months, 12% (N=2) had SD for less than 6 months (figure 1 ab 39–88) and median PFS was 9.5 months (4.99-infinity); 6-month OS was 88% (74–100%) and median OS was not reached. One patient died while enrolled. 94.1% (N=16) experienced toxicities with 52.9% (N=9) experiencing grade 3–5 toxicities. The most common adverse events were fatigue (41.2%, N=7), elevated lipase (29.4%, N=5), acute kidney injury, diarrhea, muscle weakness, anorexia, pruritis, nausea and alanine aminotransferase elevation (21.1%, N=3 each). The most common immune-mediated adverse events were acute kidney injury and elevated lipase (29.4%, N=5 each). Conclusions Combination therapy with ipilimumab plus nivolumab in thyroid cancer resulted in an ORR of 12% with two partial responses in seventeen treated patients. Trial Registration NCT02834013 Ethics Approval The study was approved by the NCI Adult Central Institutional Review Board, approval number 02834013.

Purpose: In metastatic castrate-sensitive prostate cancer (mCSPC), combined androgen axis inhibition is a standard of care. Noninvasive biomarkers that guide initial therapy decisions are needed. We hypothesized that CellSearch circulating tumor cell (CTC) count, an FDA-cleared assay in metastatic castrate-resistant prostate cancer (mCRPC), is a relevant biomarker in mCSPC. Experimental Design: SWOG S1216 is a phase III prospective randomized trial of androgen deprivation therapy (ADT) combined with orteronel or bicalutamide for mCSPC. CellSearch CTC count was measured at registration (baseline). Prespecified CTC cut-off points of 0, 1–4, and ≥5 were correlated with baseline patient characteristics and, in a stratified subsample, were also correlated with two prespecified trial secondary endpoints: 7-month PSA ≤0.2 ng/mL versus 0.2–4.0 versus >4.0 (intermediate endpoint for overall survival); and progression-free survival (PFS) ≤ versus >2 years. Results: A total of 523 patients submitted baseline samples, and CTCs were detected (median 3) in 33%. Adjusting for two trial stratification factors (disease burden and timing of ADT initiation), men with undetectable CTCs had nearly nine times the odds of attaining 7-month PSA ≤ 0.2 versus > 4.0 [OR 8.8, 95% confidence interval (CI), 2.7–28.6, P < 0.001, N = 264] and four times the odds of achieving > 2 years PFS (OR 4.0, 95% CI, 1.9–8.5, P < 0.001, N = 336) compared with men with baseline CTCs ≥5. Conclusions: Baseline CTC count in mCSPC is highly prognostic of 7-month PSA and 2-year PFS after adjusting for disease burden and discriminates men who are likely to experience poor survival outcomes.

SWOG1314 is a randomized phase II study of co-expression extrapolation (COXEN) with neoadjuvant chemotherapy for localized, muscle-invasive bladder cancer. COXEN is a biomarker approach in which predictive biomarkers are developed using in vitro data, which may then be applied directly into a clinical testing application. Two separate Gene Expression Models (GEMs), one for the Methotrexate, Vinblastine, Doxorubicin, Cisplatin (MVAC) regimen and another for gemcitabine plus cisplatin (GC) were tested in S1314. The lessons learned from the development and operationalization of the S1314 clinical trial are described in detail, which may help to inform the future trials of predictive biomarkers for urothelial carcinoma in the neoadjuvant setting. Specific areas addressed include: The need for broad support from the bladder cancer community, planning for non-evaluable subjects, defining adequate neoadjuvant treatment, defining adequate tissue collection, setting expectations in phase II clinical studies of predictive biomarkers, and maximizing the impact of the samples collected in these studies for broader biomarker development. With a large number of newly available treatments in advanced urothelial carcinoma in the last few years, more investigations of these agents in the neoadjuvant setting is anticipated. There will be a great need for the development of predictive biomarkers in conjunction with the use of these agents in the preoperative setting. Insights from S1314 may provide useful information and lessons learned in this development.

LBA4500 Background: Patients (pts) who undergo resection of renal cell carcinoma (RCC) with curative intent remain at risk for disease relapse. We conducted a phase III, double-blind, placebo (PB)-controlled, intergroup study to determine the effect of adjuvant treatment with the mTOR inhibitor everolimus (EVE) on recurrence-free survival (RFS). Methods: Pts with treatment-naïve, non-metastatic, fully-resected RCC at intermediate high- (pT1 G3-4 N0 to pT3a G1-2 N0) or very high-risk (pT3a G3-4 to pT4 G-any or N+) for recurrence were randomized 1:1 to EVE 10 mg PO daily x 54 weeks or PB within 12 weeks of radical or partial nephrectomy. Randomization was stratified by risk group, histology (clear vs. non-clear cell), and performance status (0 vs. 1). RFS was the primary end point; secondary endpoints included overall survival (OS) and adverse events (AEs). The study was designed to detect an 18% reduction in the risk of RFS with EVE compared to PB, corresponding to an improvement of median RFS from 6.75 (based on E2805 ASSURE) to 8.23 years. Final analysis, using a stratified logrank test, was to occur after 804 total events or by 3/2022, whichever occurred first. Results: Between 4/2011 and 9/2016, 1545 pts were randomized to EVE (n = 775) or PB (n = 770). Overall pt characteristics included: intermediate high-/very high-risk 45%/55%; clear cell/non-clear cell 83%/17%. The DSMC recommended study continuation after each of 4 pre-specified interim analyses. 556 DFS events among 1499 eligible pts occurred by the time of final study analysis on 2/23/2022. The median follow-up was 76 months. RFS was improved with EVE vs. PB (HR 0.85, 95% CI, 0.72 – 1.00; P1-sided= 0.0246), narrowly missing the pre-specified, one-sided significance level of 0.022 which accounted for interim analyses. Median RFS was not reached; the 6-year RFS estimate was 64% for EVE and 61% for PB. RFS improvement with EVE vs. PB was observed in the very high-risk group (HR 0.79, 95% 0.65-0.97; P1-sided= 0.011) but not in the intermediate high-risk group (HR 0.99, 95% CI 0.73-1.35, P1-sided= 0.48) ( P for interaction = 0.22). With 290 deaths, OS was similar between arms (HR 0.90, 95% CI, 0.71 – 1.13; P1-sided= 0.178). Fewer pts completed all 54 weeks of study treatment in the EVE group (45% v 69%). In the EVE group, 37% withdrew due to AEs (vs 5% in PB). Grade 3-4 AEs occurred in 46% of pts treated with EVE and 11% with PB. The most common grade 3-4 AEs were mucositis (14% v 0%), hypertriglyceridemia (11% vs. 2%), and hyperglycemia (5% vs. 0%). Conclusions: Adjuvant EVE improved RFS in RCC pts after nephrectomy, but the nominal significance level was narrowly missed. The RFS improvement was seen despite a high rate of early treatment discontinuation. A 21% improvement in RFS with EVE was observed in pts with very high-risk disease, a group for whom adjuvant therapy may be most relevant. Clinical trial information: NCT01120249.

TPS4608 Background: UC is 2nd most common genitourinary cancer. Current SOC offers platinum-based (PB) first line chemotherapy (chemo) with ddMVAC or gemcitabine-cisplatin (GC) regimens. For cisplatin ineligible patients (pts), SOC includes gemcitabine-carboplatin (GCa), and in select pts pembrolizumab. Erdafitinib is approved for pts with FGFR alterations and Enfortumab vedotin (EV) is approved for previously treated pts. A phase I/II CTEP study of eribulin (E) for metastatic UC (mUC) established the activity of E in UC with objective response rate (ORR) of 37.5% and a median progression free survival (PFS) of 4.1 months (mo) and median overall survival (OS) of 9.5 mo (N = 150). A phase II CTEP study of gemcitabine-eribulin (GE) in cisplatin ineligible mUC showed an ORR of 50%, median OS of 11.9 mo and median PFS of 5.3 mo (N = 24). The most common Grade 3-4 toxicities included: neutropenia 63%, anemia and fatigue 29%. Pts with liver metastases benefited from therapy with 5 responders in 7 pts for GE vs 12 out 49 E. Methods: This is a phase III, randomized 3 arm study comparing E vs. GE vs. SOC (docetaxel, paclitaxel, or gemcitabine). E is given at 1.4mg/m2 on day (D) 1 and 8 of a 21 D cycle. In the GE arm, gemcitabine is added to E at 1000 mg/m2 dose to D1 and D8. SOC follows standard dosing of the agents. There is no limit to the number/sequence of prior regimens. A simplified summary of eligibility criteria is presented here. All pts must have: received frontline systemic treatment such as PB chemo or a non-platinum regimen. received PD1/PDL1 Ab or be deemed ineligible for PD1/PDL1 Ab. received EV. Assuming a median OS for the SOC arm of 7 mo the study seeks to find at least a 50% increase in median OS to 10.5 mo (Hazard Ratio (HR) = 0.667). One-sided 0.0125 type I error to account for testing of two primary hypotheses (Each arm vs. SOC). 87% power to detect a 3.5 mo improvement in OS. We require 140 eligible (155 total) pts in each arm for a total of 465. The study was activated in Feb 2021 and accrual is ongoing. Clinical trial information: NCT04579224.

4581 Background: SWOG S1314 (NCT02177695) was designed to validate the CoXEN classifier as a predictive biomarker in pts undergoing cystectomy after NAC. We repurposed banked DNA samples and prospective trial data from S1314 to further validate the predictive ability of the Philadelphia 4 gene signature (P4GS: any mutation in ATM, RB1, FANCC, ERCC2) to predict pT0 as previously reported (PMID: 26238431) and used in the RETAIN trial (NCT02710734). The RETAIN trial prospectively enrolled pts to receive NAC (DDMVAC) followed by allocation to bladder observation vs. intervention (cystectomy or RT) based on clinical evaluation and presence vs absence of P4GS. The primary objective of this correlative investigation was to determine whether presence of P4GS is predictive of pT0 at surgery. Methods: Eligibility for S1314 included cT2-T4a N0 M0 MIBC, cisplatin eligible, with plan for cystectomy; 237 pts were randomized between ddMVAC and gem/cis (GC) using standard dose/schedule. Of 167 pts who were evaluable for the original COXEN analysis (received 3+ cycles of chemo and evaluable for path response) adequate banked DNA was available for 105. Next-generation sequencing using the CARIS 592 Gene Panel (Caris Life Sciences, Phoenix, AZ) was performed. Pathogenic mutation or VUS of ATM, RB1, FANCC or ERCC2 was noted as present or absent for each pt and correlated with pT0 using logistic regression, adjusting for clinical stage. Results: Among the 105 pts, 51% ddMVAC, 49% GC. 15% female, 95% white, 15% clinical stage T3/T4a Prevalence of mutations: ATM (24%), ERCC2 (17%), FANCC (4%), RB1 (24%) and any variant 53%. Presence of any mutation correlated with pT0 (p = 0.0006), sensitivity 79%, specificity 59%. This association did not vary by treatment arm (MVAC vs. GC). The table below shows the contributions of each of the 4 genes with the greatest contribution from ATM and ERCC2. FANCC was non-contributory due to low prevalence. Conclusions: Patients with a mutation in ATM, RB1, FANCC or ERCC2 (P4GS) have a statistically significantly higher odds of a pT0 with GC or MVAC compared to those who do not have any variant. This signature was used to prospectively allocate patients to bladder observation as part of the RETAIN trial previously reported (ASCO GU 2021). RETAIN completed enrollment, final analysis of the primary endpoint – 2-year metastasis free survival – is expected later in 2022. Clinical trial information: NCT02177695.

4506 Background: Neoadjuvant chemotherapy is the standard of care in muscle-invasive bladder cancer patients. However, treatment is intense, the overall benefit is small, and there is no established marker to identify patients who benefit most. The aim of the study is to characterize cell-free DNA (cfDNA) methylation from patients receiving neoadjuvant chemotherapy in SWOG S1314, a prospective cooperative group trial, and to correlate the methylation signatures with pathologic response. Methods: Blood samples were collected prospectively from 73 patients before and during standard neoadjuvant chemotherapy. At radical cystectomy, pathologic response was documented. Plasma cfDNA was profiled using Infinium MethylationEPIC BeadChip array. Differential methylation between pathologic responders (≤pT1N0M0) and non-responders was analyzed, and a Random Forest model was used to generate a classifier predictive of treatment response. Results: Using pre-chemotherapy plasma cfDNA, we developed a methylation-based response score (mR-score) predictive of pathologic response. The mR-score also could be calculated using plasma samples collected after the first cycle of neoadjuvant chemotherapy, resulting in a similar predictive ability. Furthermore, we used cfDNA methylation data to calculate the circulating bladder DNA fraction, which had a modest but independent predictive ability for treatment response. When we combined the mR-score and circulating bladder DNA fraction, we successfully predicted pathologic response outcomes in 79% of patients based on their plasma collected before chemotherapy and after 1 cycle of chemotherapy. Conclusions: Our study provides proof of concept that cfDNA methylation may be used to predict treatment response in bladder cancer patients receiving neoadjuvant chemotherapy. Clinical trial information: NCT02177695.

536 Background: This trial evaluated COXEN, a gene expression model, as a predictive biomarker in muscle-invasive bladder cancer (BC) patients randomized to Gemcitabine-Cisplatin (GC) or dose-dense Methotrexate-Vinblastine-Adriamycin/doxorubicin-Cisplatin (ddMVAC). Primary results correlating COXEN with pathologic response at surgery have been reported. This secondary analysis includes progression-free (PFS) and overall survival (OS). Methods: Eligibility included Stage cT2-T4a N0 M0, urothelial BC (mixed histology allowed), ≥ 5 mm of viable tumor, cisplatin eligible, with plan for cystectomy. 237 patients were randomized between ddMVAC, given every 14 days for 4 cycles, and GC, given every 21 days for 4 cycles. Cox regression was used to evaluate COXEN score or treatment arm association with PFS and OS, adjusting for stratification factors (stage and PS). Results: 167 patients were included in the primary COXEN analysis all having either at least 3 cycles of chemo and surgery within 100 days of last chemo or having progressed while receiving chemo. The COXEN scores were not significantly prognostic for OS or PFS in their respective arms; the COXEN GC score was a significant predictor for OS in pooled arms. OS and PFS data are shown for both scores in the table. In the intent to treat analysis (n=227), there was no significant difference in OS or PFS for ddMVAC versus GC (for OS, HR =0.87, 95% CI 0.54-1.40), p = 0.57); for PFS (HR= 0.76 95% CI 0.58-1.01, p = 0.055). Association of path response with OS will be presented. Conclusions: The COXEN GC score may be prognostic of survival in those receiving platinum-based neoadjuvant treatment. The randomized, prospective design provides estimates of OS and PFS for GC and ddMVAC that appear comparable, but this phase II trial is underpowered for definitive comparisons. The prospective data and correlative samples from S1314 will allow for further assessment of COXEN and other RNA and DNA based predictive and prognostic biomarkers. Clinical trial information: NCT02177695. [Table: see text]

TPS591 Background: Neoadjuvant cisplatin-based combination chemotherapy improves survival in cisplatin-eligible patients (pts) with muscle invasive bladder cancer (MIBC). An unmet need exists in cisplatin-ineligible pts with MIUC who are offered upfront surgery. Neoadjuvant immune checkpoint inhibitors (ICIs) have been demonstrated to be safe and active although the benefit may not extend to the majority of pts. The combination of GCa and an ICI has been demonstrated to be safe and active in cisplatin-ineligible metastatic urothelial carcinoma. In the neoadjuvant setting, combination GCa and an ICI may improve outcomes across a broad group of MIUC by delivering early systemic therapy to pts with cisplatin-ineligible MIUC. We hypothesized that the combination of GCa and avelumab, a PD-L1 inhibitor, may improve pathologic complete remissions (pCR) and long-term outcomes compared to upfront surgery for MIUC (S2011, NCT04871529). Methods: This multicenter, randomized (1:1), open-label phase II trial is comparing the combination of GCa and avelumab (Arm A) as neoadjuvant therapy vs. upfront surgery (Arm B) for pts with cisplatin-ineligible MIUC including MIBC and high-risk upper tract urothelial carcinoma (UTUC). Adjuvant therapy following radical cystectomy, nephroureterectomy or ureterectomy is deferred to investigator discretion in both arms. Eligible pts include those with MIBC or high-grade UTUC with a predominant urothelial component who are cisplatin-ineligible (≥1 of: Zubrod performance status [PS] = 2, creatinine clearance [CrCl] 30 to < 60 ml/min, neuropathy > grade 1, hearing loss > grade 1, congestive heart failure > grade 2). The primary objective is pCR. The stratification factors include clinical stage (cT2N0M0 vs cT3-4aN0M0), Zubrod-PS (0-1 vs 2), CrCl (30 to < 60 vs ≥ 60 ml/min). With 178 evaluable pts, the trial will have a power of 90% (using a 1-sided alpha 0.05) to detect pCR rate improvement from 15% to 35%. The secondary objectives are toxicities, resectability rates, surgical complications, event-free survival (EFS) and overall survival (OS). Correlative studies include tumor molecular profiling, blood immune studies, circulating tumor-DNA profiling and radiomics. Arm A receives gemcitabine 1000 mg/m2 IV days 1, 8 every 3 weeks x 4 cycles, carboplatin AUC 4.5 (escalated to AUC 5 from cycle 2 if tolerated in cycle 1) IV day 1 every 3 weeks x 4 cycles and avelumab 800 mg IV day 1 every 2 weeks x 6 cycles. Surgery is performed 4-8 weeks after the last neoadjuvant administration. The trial is funded by NIH/NCI grants U10CA180888, U10CA180819, U10CA180821, U10CA180820, U10CA180868, and in part by EMD Serono, as part of an alliance between the healthcare business of Merck KGaA, Darmstadt, Germany (CrossRef Funder ID: 10.13039/100009945) and Pfizer. Clinical trial information: NCT04871529.

BackgroundSkeletal metastases often occur in men with castration-resistant prostate cancer (CRPC) where bone biomarkers are prognostic for overall survival (OS). In those with highly elevated markers, there is preferential benefit from bone-targeted therapy. In the phase IIIS0421 docetaxel +/- atrasentan trial, clinical covariates and bone biomarkers were analyzed to identify CRPC subsets with differential outcomes.Subjects and methodsMarkers of bone resorption [N-telopeptide-NTx; pyridinoline-PYD] and formation [C-terminal collagen propeptide-CICP; bone alkaline phosphatase-BAP] were measured in pre-treatment sera. Bone biomarkers and clinical covariates were included in a Cox model for OS; bone markers were added in a stepwise selection process. Receiver operating characteristic (ROC) curves were constructed for risk factor models +/- bone markers. Significant variables were allowed to compete in a classification and regression tree (CART) analysis. Hazard ratios(HR) were calculated by comparing OS in each of the terminal nodes to a reference group in a Cox model.Results750 patients were included. Each bone marker significantly contributed to the risk factor-adjusted OS Cox model, with higher levels associated with worse OS. BAP (HR = 1.15, p = 0.008), CICP (HR = 1.27, p

Background: Papillary renal cell carcinoma (pRCC) is associated with EGFR expression and activation of MET signaling pathway. A randomized multicenter parallel two-stage phase II trial of MET inhibitor tivantinib alone or in combination with EGFR inhibitor erlotinib was conducted in patients with pRCC. Methods: Patients with advanced pRCC and 0-1 prior systemic therapy were randomly assigned to tivantinib 360 mg BID (Arm 1) or tivantinib 360 mg BID plus erlotinib 150 mg daily (Arm 2). Target max accrual was 70 patients (35 per arm) with interim analysis planned after enrollment of 20 patients per arm. Results: Six % of patients had type 1 pRCC, 42% had type 2, and 52% had no subtype assigned. The study was closed after the first stage when both arms yielded RR of 0%. Median progression free survival (PFS) was 2.0 and 3.9 months, and OS was 10.3 and 11.3 months in Arms 1 and 2 respectively. Treatment was well tolerated. Exome of tumor tissue from 16 patients were successfully sequenced using Agilent SureSelect probes. Only 1 of 16 samples harbored MET mutation. Other mutations associated primarily with type 2 pRCC were noted and included CDKN2A, PBRM1, SETD2, KDM6A, FAT1 and NF2. Conclusions: Tivantinib - either alone or in combination with erlotinib has no clinical activity in patients with advanced pRCC. The S1107 cohort had a low proportion of patients with MET alterations. MET remains a reasonable therapeutic target in pRCC, but selection of patient subsets exhibiting MET activation may be required to better benefit from therapy with MET inhibitors.

Background Previous studies suggest circulating, blood-based microRNAs (miRNAs) may serve as minimally invasive prostate cancer biomarkers, however there is limited data from prospective clinical trials. Here, we explore the role of candidate plasma miRNAs as potential biomarkers in the SWOG 0925 randomized phase II study of androgen deprivation combined with cixutumumab versus androgen deprivation alone in patients with new metastatic hormone-sensitive prostate cancer. Methods Correlative biospecimens, including circulating tumor cells (CTCs) and plasma for miRNA analysis, were collected at baseline and after 12 weeks on treatment from 50 patients enrolled on SWOG 0925. Circulating microRNAs were quantified using real-time RT-PCR microRNA array that allowed specific analysis of previously identified candidate miRNAs (miR-141, miR-200a, miR-200b, miR-210, and miR-375) as well as discovery analysis to identify new candidate miRNAs. MiRNA levels were correlated to previously reported CTC counts using CellSearch® (Veridex) and with the primary study outcome of 28-week PSA response (≤0.2, 0.2 to ≤4.0, or >4.0 ng/mL), previously shown to correlate with overall survival. Results We observed a correlation between baseline circulating miR-141, miR-200a, and miR-375 levels with baseline CTCs. Baseline miR-375 levels were associated with 28-week PSA response (≤0.2, 0.2 to ≤4.0, or >4.0 ng/mL, P = 0.007). Using ROC curve analysis, there was no significant difference between baseline miR-375 and baseline CTC in predicting 28-week PSA response (≤0.2 vs >0.2 ng/mL). To discover novel candidate miRNAs, we analyzed 365 miRNAs for association with the 28-week PSA response endpoint and identified new candidate miRNAs along with the existing candidates miR-375 and miR-200b (P = 0.0012, P = 0.0046, respectively. Conclusions Baseline plasma miR-141, miR-200a, and miR-375 levels are associated with baseline CTC count. Baseline miR-375 was also associated with the trial endpoint of 28-week PSA response. Our results provide evidence that circulating miRNA biomarkers may have value as prognostic biomarkers and warrant further study in larger prospective clinical trials.

Author(s): Synold, Timothy W; Plets, Melissa; Tangen, Catherine M; Heath, Elisabeth I; Palapattu, Ganesh S; Mack, Philip C; Stein, Mark N; Meng, Maxwell V; Lara, Primo; Vogelzang, Nicholas J; Thompson, Ian Murchie; Ryan, Christopher W | Abstract: BackgroundS0931 is assessing recurrence-free survival in renal cell carcinoma (RCC) patients randomized to receive everolimus (EVE) versus placebo for one year following nephrectomy. Due to a higher than expected dropout rate, we assessed EVE trough levels in the adjuvant setting to evaluate the relationship between EVE exposure and probability of toxicity.MethodsPatients received 10 mg daily EVE for nine 6-week cycles. Pre-dose whole blood samples were collected pre-cycle 2 and pre-cycle 3 and analyzed for EVE. Patients with pre-cycle 2 and/or pre-cycle 3 EVE results were used in the analysis. Patients were segregated into quartiles (Q) based on EVE levels and logistic regression was used to model the most common adverse event outcomes using EVE trough as a predictor. Hazard and odds ratios were adjusted for age, BMI and performance status.ResultsA total of 467 patients were included in this analysis. Quartiles normalized to an EVE dose of 10 mg/day were l 9.0, 9.0-12.9, 12.9-22.8, and g 22.8 ng/mL, respectively. EVE trough levels increased with increasing age (p l 0.001). Furthermore, EVE trough levels were higher in men than women (19.4 versus 15.4 ng/mL, p = 0.01). Risk of grade 2 + triglycerides was increased in Q2 and Q3 vs Q1 (OR = 2.08; p = 0.02 and OR = 2.63; p = 0.002). Risk of grade 2 + rash was increased in Q2 and Q4 vs Q1 (OR = 2.99; p = 0.01 and OR = 2.90; p = 0.02). There was also an increased risk of any grade 3 + tox in Q2 vs Q1 (OR = 1.71; p = 0.05).ConclusionsWe identified significant gender and age-related differences in EVE trough levels in patients receiving adjuvant treatment for RCC. Furthermore, our analysis identified significant associations between EVE exposure and probability of toxicity.

5001 Background: Tak is an oral selective nonsteroidal 17, 20-lyase inhibitor that blocks the synthesis of gonadal and adrenal androgens. We evaluated the clinical benefit of Tak with ADT in pts with newly diagnosed mHSPC. Methods: Pts with mHSPC with a Zubrod performance status (PS) of 0-2 and a PSA of ≥ 2 ng/ml were randomized 1:1 to ADT+Tak (300 mg twice daily) or ADT+Bic (50 mg daily). Stratification factors included PS (0-1 vs ≥2), extent of disease (minimal vs extensive), and receipt of ADT prior to registration (yes vs no). The primary endpoint was overall survival (OS). Secondary endpoints were progression free survival (PFS; based on PSA, imaging or clinical progression), PSA at 7 months (≤0.2 vs 0.2 < PSA; ≤-4 vs. > 4 ng/ml) and adverse event (AE) profile. With 2.75 yrs to accrue 1,186 eligible pts and 3 additional yrs of follow-up, we would have 90% power to determine a 33% improvement in OS from 54 to 72 mos (1-sided α = 0.025). A final analysis was pre-specified after 523 deaths using a 1-sided α = 0.022 to account for interim analyses. Results: Between 3/2013 and 7/2017, 1,313 pts were randomized and 1,279 were included in the intention-to-treat (ITT) analysis (32 pts were ineligible and 2 pts withdrew consent). Median age was 68 yrs and 10% of subjects were Black. Median PSA was 30 ng/mL (range 2-6710) and 49% of pts had extensive disease. After a median follow-up of 4.9 yrs, PFS and PSA response were significantly improved with Tak over Bic but no significant improvement in OS was observed (Table). More grade 3/4 AEs occurred in Tak vs. Bic arms (43% vs. 14%), and included hypertension (20% vs. 5%) and fatigue (5% vs. 2%). Five pts in Tak and 1 pt in the Bic arm had grade 5 AE. Conclusions: Despite clinically meaningful improvement in various outcome measures with Tak+ADT over Bic+ADT in this representative population of mHSPC, the improvement in OS did not meet the pre-specified criteria for statistical significance. The median OS of 70 mos in the control arm (standard ADT) was higher than that reported in contemporary phase 3 trials in this setting, and 16 mos higher than originally estimated. This trial sets a new landmark for survival estimates when pts with mHSPC have access to multiple approved subsequent life-prolonging therapies. Funding: NIH/NCI/NCTN grants U10CA180888, U10CA180819, U10CA180820; U10CA180821; and in part by Millennium Pharmaceuticals, Inc. (Takeda Pharmaceutical Company LTD) Clinical trial information: NCT01809691. [Table: see text]

4541 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. 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 the 18 month results for all eligible patients who received at least one protocol treatment. The co-primary endpoints were pathological complete response (CR) rate at 6 months in patients with CIS (reported at ASCO 2020), and event-free survival (EFS) in all patients at 18 months using Kaplan-Meier methods (KM), conditional on a positive CIS response rate. A sample size of 135 evaluable patients provided 93% statistical power for detecting a 30% 18-month EFS rate versus 20% using a one-sided alpha = 0.05. EFS in the subset with Ta/T1 disease and duration of response in CIS patients were secondary endpoints. Results: 172 patients were enrolled, 166 received at least one dose of atezolizumab and are included in the safety analysis, and, of those, 128 were eligible and included in the efficacy analysis. As previously reported, 20 (27%) out of 74 patients with CIS attained a pathologic CR at 6 months. The KM estimate of 12 month (actual 11.9 mo) duration of response after 6 month CR for CIS patients was 54% (95% CI 30%, 78%) and the median duration of response was 16.5 months. The KM EFS rate at 18 months in 74 patients with CIS was 17% (90% CI 9%, 25%). The 18 month KM EFS rate in the overall population of 128 patients with Ta, T1 and CIS was 29% (90% CI 22%, 36%). The 18 month actuarial EFS rate in 54 patients with Ta/T1 disease was 45% (90% CI 34, 57%). Any possibly or probably treatment-related adverse event (TRAE) was observed in 142 out of 166 (86%) patients who received any atezolizumab regardless of eligibilty. The most frequent TRAEs were fatigue 72 (43%), diarrhea 34 (20%), and anemia 38 (23%). Grade 3-5 TRAEs occurred in 28 (17%) patients, including rash in 4 (2%), hyponatremia in 4 (2%), hypertension in 3 (2%) and elevated liver function tests in 3 (2%). There were two treatment-related deaths (sepsis and respiratory failure due to myasthenia gravis). Conclusions: The observed response of atezolizumab at 6 and 18 months in patients with BCG-unresponsive CIS suggests that this could be a valuable treatment to address a critical unmet need in this patient population. The 18 month EFS in patients with Ta/T1 disease suggests activity in this patient subset. This trial provided no new safety concerns. Funding: NIH/NCI grants: CA180888, CA180819, CA180820, CA180821, CA180863 and in part by Genentech. Clinical trial information: NCT02844816.

428 Background: Trimodality therapy (TMT) with maximal TURBT followed by chemoradiation(CRT) is a standard of care for select patients with muscle invasive bladder cancer (MIBC). This trial evaluates the activity of atezolizumab (atezo) in MIBC in combination with TMT. This trial was designed with pre-specified safety analyses of the first 80 patients (40 in each arm). At the time of SWOG fall 2020 DSMC report deadline we had enrolled 84 patients but data on only 73 patients were available. The same data are being submitted to ASCO GU meeting. Methods: This trial is testing atezo every 3 weeks for 6 months given concurrently and adjuvantly with CRT vs. CRT alone in 475 patients with MIBC T2-T4aN0M0 disease. Patients are stratified based on PS; T2 vs T3 or T4; choice of chemotherapy; and radiation field (bladder only vs small pelvis). Patients undergo biopsy 3 months after finishing CRT to assess treatment response. Patients are followed for 5 years for recurrence or survival. This trial was not preceded by a phase I study but was designed with a safety run in of 80 patients. Study team agreed on the study design based on available data from other tumor types and initial experience from investigators running smaller similar trials. It was pre-specified that if we observe more than 25% patients having grade 3-5 colitis or cystitis in the atezo arm or any other toxicity which is deemed clinically significant and related to atezo, the trial investigators and DSMC would consider stopping further enrollment. Results: 36 patients were enrolled on the TMT alone arm and 37 patients on the TMT + atezo arm. No grade 3 or higher colitis was reported in the atezo arm. Only one patient had treatment related grade 3 radiation cystitis which was diagnosed after finishing atezo treatment. No steroids were given. Overall 23 grade 3 or higher toxicity events were reported in the atezo arm vs 11 in non- atezo arm. Most common toxicity was hematological which was considered non-immune related. None of the grade 3 or higher toxicities were considered to be immune related by the treating investigator. Conclusions: There is no evidence of increased immune related grade 3-5 AEs.DSMC has recommended to continue enrollment. Adverse Events with No Entries for Grades 3 to 5 Have Been Suppressed Clinical trial information: NCT03775265 . [Table: see text]

270 Background: MET signaling is a key molecular driver in pRCC. Given that there is no optimal therapy for metastatic pRCC, we sought to compare an existing standard (sunitinib) to putative MET kinase inhibitors. Methods: Eligible patients had pathologically verified pRCC, Zubrod performance status 0-1, and measurable metastatic disease. Patients may have received up to 1 prior systemic therapy excluding VEGF-directed agents. Patients were randomized 1:1:1:1 to receive either sunitinib 50 mg po qd (4 wks on/2 wks off), cabozantinib 60 mg po qd, crizotinib 250 mg po bid, or savolitinib 600 mg po qd. Patients were stratified by prior therapy and pRCC subtype (I vs II vs not otherwise specified [NOS]) based on local review. The primary objective was to compare progression-free survival (PFS) for each experimental arm versus sunitinib. With 41 eligible patients per arm, we estimated 85% power to detect a 75% improvement in median PFS with a 1-sided alpha of 0.10 using intent-to-treat analysis. A pre-planned futility analysis was performed after 50% of PFS events occurred. Secondary endpoints included toxicity, response rate, and overall survival. Results: Between 4/2016 and 12/2019, 152 patients were enrolled; 5 were ineligible. Median age was 66 (range:29-89) and 76% were male; 92% had no prior therapy. By local pathologic review, 18%, 54% and 28% of patients were characterized as having type I, type II and NOS histology, respectively. In contrast, the frequency of type I, type II, and NOS by central review was 30%, 45% and 25%, respectively. Accrual to the savolitinib and crizotinib arms was halted early for futility (PFS hazard ratio > 1.0 for both); accrual continued to completion in the sunitinib and cabozantinib arms. Median PFS was significantly higher with cabozantinib relative to sunitinib (Table). Grade 3 or 4 adverse events occurred in 69%, 72%, 37% and 39% of patients receiving sunitinib, cabozantinib, crizotinib and savolitinib, respectively; one grade 5 adverse event was seen with cabozantinib. Overall survival and response data will be presented. Conclusions: In this multi-arm randomized trial, only cabozantinib resulted in a statistically significant and clinically meaningful prolongation of PFS in pRCC patients compared to sunitinib. These data support cabozantinib as a reference standard for eligible patients with metastatic pRCC. Clinical trial information: NCT02761057 . [Table: see text]

Background: The potential therapeutic benefits of checkpoint inhibitors and their application to many different tumor types has been a key factor in the advancement of medical oncology since their first approval for metastatic melanoma in 2011. However, their efficacy in rare tumor types remains to be seen. This paper presents the results of combination therapy with both anti-CTLA and anti-PD-1 in the small bowel cohort of SWOG S1609 Dual Anti-CTLA-4 & Anti-PD-1 blockade in Rare Tumors (DART). Methods: This study is designed as a prospective, open-label, multicenter phase 2 clinical trial of ipilimumab (1mg/kg intravenously every 6 weeks) plus nivolumab (240mg intravenously every 2 weeks) in rare tumors. Here we report the outcomes from patients diagnosed with small bowel cancer (SBC). The primary endpoints included overall response rate (ORR) (RECIST v1.1) (complete response (CR) and partial responses (PR)); progression-free survival (PFS), overall survival (OS), stable disease >6 months, and toxicity were the secondary endpoints. Results: Twenty five patients were registered to the cohort and twenty three received therapy. The duodenum was the primary site of origin in 52% (N=11), 14% (N=3) arose in the ileum and 14% (N=3) arose in the jejunum. The primary site of origin was unknown in 19% (N=4). The overall response rate was 8% (CR, 4%, N= 1; PR, 4%, N= 1). The median PFS was 2 months; 6-month OS was 48% and median OS 6 months. The most common toxicities were diarrhea and fatigue (both 17%) followed by dyspnea (13%) with diarrhea, increased bilirubin, colitis and elevated lipase (all 4.3%) as the most common grade 3-5 immune-related adverse events. Conclusions: Combination therapy with ipilimumab plus nivolumab in small bowel tumors resulted in an overall response rate of 8% with one partial and one complete response in twenty three treated patients. Citation Format: Young Kwang Chae, Megan Othus, Sandip Pravin Patel, Mark Zalupski, Anup Kasi, Maged Khalil, Aparna Kalyan, Blase Polite, Sarah Fenton, Sewan Gurung, Christine M. McLeod, Francis Giles, Helen X. Chen, Elad Sharon, Edward Mayerson, Melissa Plets, Christopher W. Ryan, Charles D. Blanke, Razelle Kurzrock. A phase II basket trial of dual anti-CTLA-4 and anti-PD-1 blockade in rare tumors (DART) SWOG S1609: The small bowel tumor cohort [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3417.

Background: Since their first approval in 2011 for metastatic melanoma, checkpoint inhibitors have been successfully applied to multiple tumor types. To date, the potential role for these treatments in rare solid tumors has not been well studied. We report the results of three salivary gland neoplasm cohorts of SWOG S1609 Dual Anti-CTLA-4 & Anti-PD-1 blockade in Rare Tumors (DART) trial. Methods: We performed a prospective, open-label, multicenter phase 2 clinical trial of ipilimumab (1mg/kg intravenously every 6 weeks) plus nivolumab (240mg intravenously every 2 weeks) in multiple tumor types. Here, we report the results found in three salivary gland neoplasm cohorts that include patients with salivary gland tumor types arising in major salivary glands (cohort 2), other sites of origin (cohort 3) and adenoid cystic carcinomas of any site (cohort 34). Primary endpoints included overall response rate (ORR) (RECIST v1.1) (complete response (CR) and partial responses (PR)); secondary endpoints included progression-free survival (PFS) and overall survival (OS), stable disease >6 months, and toxicity. Results: Twenty six patients with adenoid cystic salivary gland tumors and thirty five patients with other histologic subtypes of salivary gland neoplasm received therapy. The most common site of origin was the parotid (35%; N=9 in the adenoid cystic group and 54%; N=19 in the remaining histologies). The overall ORR in the adenoid cystic group was 4% (CR, 0%; PR, 4%, N= 1) and the median PFS was 4.4 months. 6 month OS was 84% and median OS was 12 months. In the remaining histologic subtypes the ORR was 9% (CR, 0%; PR, 9%, N=3) and the median PFS was 4.6 months. 6-month OS was 89%, median OS was not reached. The most common toxicities were fatigue (39%) and diarrhea (26%), with diarrhea (8%) as the most common grade 3-5 immune-related adverse event. Conclusions: In salivary gland tumors, combination therapy with ipilimumab plus nivolumab resulted in a 4% ORR in adenoid cystic carcinoma and 9% in other histologies combined. Citation Format: Young Kwang Chae, Megan Othus, Sandip Pravin Patel, James P. Ohr, Francis P. Worden, Jennifer M. Suga, Aung Naing, Sarah E. Fenton, Hyunseok Kang, Sewan Gurung, Christine M. McLeod, Francis J. Giles, Helen X. Chen, Elad Sharon, Edward Mayerson, Melissa Plets, Christopher Ryan, Charles D. Blanke, Razelle Kurzrock. A phase II basket trial of dual anti-CTLA-4 and anti-PD-1 blockade in rare tumors (DART) SWOG S1609: The salivary gland tumor cohort [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3418.

5506 Background: In mCSPC, androgen deprivation therapy (ADT) combined with chemotherapy or androgen receptor signaling inhibition (ARSI) is the new standard of care. Biomarkers that predict clinical outcomes with these therapies are needed. We hypothesized that CellSearch CTC count, an FDA-cleared biomarker in metastatic castrate resistant PC (mCRPC), may be a valuable biomarker in mCSPC. Methods: In S1216, peripheral blood was drawn with informed consent at registration (baseline), and CTCs were enumerated on the FDA-cleared CellSearch platform (Menarini) per standard manufacturer protocol. CTC counts were analyzed centrally for associations with 2 pre-specified trial intermediate endpoints: 7-month PSA (7mPSA) ≤ 0.2 ng/ml vs. 0.2–4.0 vs. > 4.0, (intermediate endpoint for overall survival, OS); and progression-free survival (PFS) < vs. > 2 years. Because OS data have not matured, analysis was pooled and equal numbers of samples were analyzed from each treatment arm and outcome measure (7mPSA and PFS) as stipulated by the Data Safety Monitoring Committee. Results: From 2014 to 2017, 523 baseline samples were collected. In the 7mPSA analysis (n = 264), CTCs were detected in 38% of men, with a median of 4 CTCs in those with detectable CTCs. In the PFS analysis (n = 336), CTCs were detected in 37% of men, with a median of 3 CTCs in those with detectable CTCs. Adjusting for disease burden (minimal vs. extensive) and ADT status (already initiated or not) at the time of CTC measurement, men with undetectable CTCs were 6.1-fold more likely to attain 7mPSA ≤ 0.2 (OR 6.1, 95% CI 2.1-17.2, p < 0.001) and 3.7-fold more likely to achieve > 2 years PFS (OR 3.7, 95% CI 1.7-8.1, p < 0.001) compared to men with baseline CTCs ≥ 5. Other cutpoints previously validated in mCRPC studies (CTC < 5 vs. ≥5 and CTCs 0 vs. ≥1) also strongly discriminated 7mPSA and PFS with statistical significance in this mCSPC cohort. Conclusions: CTC count at the start of treatment for mCSPC was highly prognostic of 7-month PSA response (intermediate endpoint for OS) and of PFS at 2 years. To our knowledge, this is the first such strong evidence from a prospective phase 3 trial of this magnitude. Additional analyses are planned when the trial is fully reported. Baseline CTC count may serve as a valuable prognostic marker to discriminate men likely to respond favorably to hormonal therapies from those who may benefit from early alternate interventions.

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 .

Background Phase 2 trials evaluating new agents for metastatic castration-resistant prostate cancer (mCRPC) have relied on bone scan and prostate-specific antigen changes to assess activity. Given the increasing detection of measurable disease, Response Evaluation Criteria in Solid Tumors (RECIST) changes warrant consideration to evaluate activity. We validated the association of RECIST 1.0 changes with survival in men with mCRPC receiving docetaxel. Patients and Methods Data for men with measurable disease from the Southwest Oncology Group (SWOG) S0421, a phase 3 trial in men with mCRPC receiving docetaxel and prednisone plus placebo or atrasentan, were used. Cox proportional hazards regression was used to evaluate the association of RECIST 1.0 outcomes within 120 days, ie, unconfirmed partial response (uPR), stable disease, and progressive disease (PD), with overall survival (OS) from day 120, adjusted for prognostic factors. Results Overall, 326 men were evaluable for landmark analysis, of whom 23 had PD, 230 stable disease, and 73 uPR. OS beyond day 120 was significantly different ( P = .004) among these subgroups, with median (95% confidence interval) OS of 7.1 (3.5-8.8), 13.4 (11.4-15.6), and 16.3 (10.0-19.6) months for those with PD, stable disease, and uPR, respectively. In a multivariable model, the hazard ratio (95% confidence interval) for patients with PD was 2.47 (1.42-4.29) compared to patients with an uPR ( P = .002). Conclusion The association of RECIST 1.0 changes with OS in men with mCRPC receiving docetaxel was validated. Given limitations of bone scan and prostate-specific antigen alterations, improvements in objective RECIST 1.0 changes should be reported in phase 2 trials before launching phase 3 trials.

Background: Immune checkpoint blockade, in particular anti-CTLA-4 and anti-PD-1-directed approaches, have improved outcomes in various tumor types. However, little is known about the efficacy of these agents in metastatic rare solid tumors. We report here the results of the neuroendocrine cohort of SWOG S1609 Dual Anti-CTLA-4 & Anti-PD-1 blockade in Rare Tumors (DART). Methods: We performed a prospective, open-label, multicenter phase 2 clinical trial of ipilimumab (1mg/kg q6 weeks) plus nivolumab (240mg intravenously every 2 weeks) across multiple cohorts of rare tumors, with the neuroendocrine cohort reported here. Pancreatic neuroendocrine tumors are currently being accrued to a separate cohort of S1609. The primary endpoint was overall response rate (ORR) by RECIST v1.1 (complete (CR) and partial responses (PR)); secondary endpoints included progression-free (PFS) and, overall survival (OS), stable disease (SD) >6 months, and toxicity. Results: Thirty-three eligible patients received therapy; 58% (N= 19) had high-grade disease; most common sites were gastrointestinal (non-pancreatic) (45%; N = 15) and lung (18%; N = 6). Patients had received a median of 2 lines of prior therapy. The overall response rate was 24% (CR, 3%; PR, 21%). Patients with high-grade neuroendocrine cancer had a 42% (8 of 19 patients) response rate vs. 0% in low/intermediate grade tumors (0/14 patients; p = 0.01). The 6-month PFS was 30%; median OS was 11 months. The most common toxicities were fatigue (30% of patients) and nausea (27%). Alanine aminotransferase (ALT) elevation (9%) was the most common grade 3-4 irAE, with no grade 5 toxicities. Conclusions: Ipilimumab plus nivolumab was well tolerated with a 42% ORR in patients with high-grade neuroendocrine cancer, regardless of primary site. Further investigation of this combination is warranted. Best Response Summary in 33 Patients with Neuroendocrine CancerResponse TypeAll Patients (n=33)High grade (n=19)Low/Intermediate grade (n=14)Complete Response (CR)1 (3%)1 (5%)0Partial Response (PR)7 (21%)7 (37%)0Stable Disease (SD)>6months2 (6%)02 (14%)SD11 (33%)3 (17%)8 (57%)Progressive Disease (PD)12 (36%)8 (42%)4 (29%)CR+PR8 (24%)8 (42%)0CR+PR+SD>6mo10 (30%)8 (42%)2 (14%) Citation Format: Sandip Pravin Patel, Megan Othus, Young Kwang Chae, Francis Giles, Donna Hansel, Preet Singh, Annette Fontaine, Manisha Shah, Anup Kasi, Tareq Al Baghdadi, Marc Matrana, Zoran Gatalica, W. Michael Korn, Jourdain Hayward, Christine MMcLeod, Helen X. Chen, Elad Sharon, Edward Mayerson, Christopher W. Ryan, Melissa Plets, Charles D. Blanke, Razelle Kurzrock. A Phase II basket trial of dual anti-CTLA-4 and anti-PD-1 blockade in rare tumors (DART) S1609: The neuroendocrine cohort [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT039.

TPS2658 Background: Immune checkpoint blockade, in particular anti-CTLA-4 and anti-PD-1-directed approaches, have improved outcomes in various tumor types. However, little is known about the efficacy of these agents in advanced rare solid tumors. We sought to investigate the activity of ipilimumab and nivolumab in previously unstudied rare solid tumors, with planned biomarker evaluation pending including whole exome sequencing, RNAseq, and multiplex immune profiling via the NCI CIMACs. Methods: We performed a prospective, open-label, multicenter phase II clinical trial of ipilimumab (1mg/kg iv q6weeks) plus nivolumab (240mg iv q2weeks) across 37 cohorts of rare tumors. Eligible patients had incurable rare cancer, defined histologically with an incidence of less than 6 in 100,000 per year, and did not have an approved or standard therapy available that had been shown to prolong overall survival. Patients were required to be 18 years of age or older, have a Zubrod performance status of 0-2, with absolute neutrophil count ≥ 1,000/mcL, platelets ≥ 75,000/mcL, hemoglobin ≥ 8 g/dL, creatinine clearance ≥ 50 mL/min, total bilirubin ≤ 2.0 x institutional upper limit of normal (IULN), AST and ALT ≤ 3.0 x IULN, TSH or free T4 serum ≤ IULN, and normal adrenocorticotropic hormone (ACTH) ≤ IULN. The primary endpoint was overall response rate (ORR) by RECIST v1.1 (complete (CR) and partial responses (PR)); secondary endpoints included progression-free (PFS) and, overall survival (OS), stable disease (SD) ≥ 6 months, and toxicity. The primary objective of this Phase II trial was to evaluate the overall response rate (ORR, confirmed complete and partial responses [CR and PR]) by RECIST v1.1. Our objective was to distinguish between a true ORR 15% (null hypothesis) versus 30% (alternative hypothesis). A Simon’s two-stage design was used, which required an analysis on the first 6 eligible patients who received therapy. If 1 or more of the 6 patients had a response (confirmed CR or PR), an additional 10 patients were to be accrued. The study was activated on 1/13/17 with the first patient treated on 3/1/17. The trial is currently open at 862 sites across the NCTN (with 352 sites having enrolled patients) and 554 patients enrolled to date. Clinical trial information: NCT02834013.

4506 Background: Both dose-dense Methotrexate-Vinblastine-Adriamycin/doxorubicin-Cisplatin (ddMVAC) and Gemcitabine-Cisplatin (GC) are accepted neoadjuvant regimens for muscle-invasive bladder cancer (BC). We investigated COXEN, a gene expression model, as a predictive biomarker. Methods: Eligibility included Stage cT2-T4a N0 M0, urothelial BC (mixed histology allowed), ≥ 5 mm of viable tumor, cisplatin eligible, with plan for cystectomy. 237 patients were randomized between ddMVAC, given every 14 days for 4 cycles, and GC, given every 21 days for 4 cycles. The primary objective was to assess whether the pre-specified dichotomous treatment-specific COXEN gene expression profile is prognostic of pT0 rate or ≤ pT1 at surgery, and to assess whether COXEN score is a predictive factor between regimens and response. Logistic regression was used to model response, adjusting for stratification factors. Results: 167 patients were included; the ddMVAC/GC arms had a median age of 65/64, PS = 0 in 80%/75%, Male proportion of 88%/79% and T2 stage of 87%/92%. All had at least 3 cycles of chemo and surgery/progression within 100 days of last chemo. There were favorable COXEN ddMVAC scores in 32% and GC score in 26%. The pT0 rates for ddMVAC and GC were 32% and 35%; the rates of ≤ pT1 were 55% and 49%, respectively. Conclusion: The COXEN scores were not significantly prognostic for response in their individual arms; The COXEN GC score was significant predictor for downstaging in pooled arms. There was no evidence of an interaction between COXEN score and regimen in predicting response. The prospective data and samples from this study will allow for further development of COXEN and other predictive biomarkers. Clinical trial information: NCT02177695. [Table: see text]

Importance Men with metastatic prostate cancer who have a poor response to initial androgen-deprivation therapy (ADT), as reflected by a prostate-specific antigen (PSA) level higher than 4.0 ng/mL after 7 months of ADT, have a poor prognosis, based on historical controls. Objective To determine the efficacy of abiraterone acetate with prednisone in these high-risk patients with a suboptimal response to hormonal induction. Design, Setting, and Participants A phase 2 single-arm study was conducted through the National Clinical Trials Network–Southwest Oncology Group. Eligible patients had metastatic prostate cancer and a PSA level higher than 4.0 ng/mL between 6 and 12 months after starting ADT. The PSA level could be rising or falling at the time of enrollment, but had to be higher than 4.0 ng/mL. No previous chemotherapy or secondary hormonal therapies were allowed, except in patients receiving a standard, first-generation antiandrogen agent with a falling PSA level at the time of enrollment; this therapy was continued in this cohort. Abiraterone acetate, 1000 mg, once daily with prednisone, 5 mg, twice daily was administered to all participants. A total of 41 men were enrolled between the trial’s activation on August 9, 2011, and closure on August 1, 2013. Data analysis was conducted from March 21 to November 29, 2016. Interventions Abiraterone acetate, 1000 mg, once daily by mouth with prednisone, 5 mg, by mouth twice daily. Main Outcomes and Measures The primary end point was a PSA level of 0.2 ng/mL or lower within 12 months of starting abiraterone acetate plus prednisone. A partial response (PR) was a secondary end point, defined as a PSA level reduction to lower than 4.0 ng/mL but higher than 0.2 ng/mL. Results Of the 41 men enrolled, 1 did not receive any protocol treatment and was excluded from analysis. The median (range) age of the 40 participants was 66 (39-85) years. Five (13%) patients achieved a PSA level of 0.2 ng/mL or lower (95% CI, 4%-27%). Thirteen (33%) additional patients achieved a partial response, with a reduction in the PSA level to lower than 4.0 ng/mL but higher than 0.2 ng/mL. Sixteen (40%) patients had no PSA response and 6 (15%) were not assessable and assumed to be nonresponders. The median progression-free survival was 17.5 months (95% CI, 8.6-25.0 months) and the median overall survival was 25.8 months (95% CI, 15.7-25.8 months). There was 1 incident each of grade 4 adverse events of alanine aminotransferase level elevation and rectal hemorrhage. Eleven patients reported grade 3 adverse events. Conclusions and Relevance This study did not reach its prescribed level of 6 PSA responses of 0.2 ng/mL or lower, although 5 responses were observed. The overall survival and progression-free survival rates observed in this trial are encouraging compared with historical controls. The therapy was generally well tolerated, without any clear signal of any unexpected adverse effects.