Acquired resistance has curtailed cancer survival since the dawn of the chemotherapy age more than half a century ago. Although the application of stem cell (SC) concepts to cancer captured the imagination of scientists for many years, only the last decade has yielded substantial evidence that cancer SCs (CSCs) contribute to chemotherapy resistance. Recent studies suggest that the functional and molecular properties of CSCs constitute therapeutic opportunities to improve the efficacy of chemotherapy. Here we review how these properties have stimulated combination strategies that suppress acquired resistance across a spectrum of malignancies. The clinical implementation of these strategies promises to rejuvenate the effort against an enduring challenge.

AT-101 was tolerable but did not extend OS when combined with DP in mCRPC; a potential benefit was observed in high-risk patients.

142 Background: Immune checkpoint inhibitor monotherapy has shown limited clinical benefit in patients (pts) with prostate cancer, likely due to an immunologically “cold” tumor microenvironment. We report preplanned interim efficacy/safety for NIVO + IPI in pts with mCRPC from CheckMate 650. Methods: Asymptomatic/minimally symptomatic pts who progressed after 2nd-generation hormone therapy and have not received chemotherapy for mCRPC (cohort 1) and pts who progressed after taxane-based chemotherapy (cohort 2) were included. Treatment was NIVO 1 mg/kg + IPI 3 mg/kg Q3W for 4 doses, then NIVO 480 mg every 4 weeks. Coprimary endpoints: objective response rate (ORR) and radiographic PFS per PCWG2. Safety is a secondary endpoint. Exploratory endpoints include correlation of biomarkers with efficacy. Results: 78 pts had a minimum follow-up of 6 months; among pts with baseline measurable disease, ORR was 26% and 10% in cohorts 1 and 2 (Table). In both cohorts, ORR was higher in pts with PD-L1 ≥1%, DNA damage repair (DDR), homologous recombination deficiency (HRD), or above-median tumor mutational burden (TMB). Of all PSA responding pts (Table), 4 had PSA <0.2 ng/mL. Grade 3–4 treatment-related adverse events occurred in 39% and 51% of pts in cohorts 1 and 2; one grade 5 event occurred in each cohort. Conclusions: In a malignancy where immune checkpoint inhibitor monotherapy has previously shown limited success, NIVO + IPI demonstrated activity in pretreated pts with mCRPC, particularly in a biomarker-enriched population, with a safety profile consistent with this dosing schedule. Further study is warranted. Clinical trial information: NCT02985957. [Table: see text]

No abstract

354 Background: Patients (pts) with mUC who progress after platinum (PLT)-based chemotherapy and immune checkpoint inhibitor (CPI) therapy have poor outcomes and limited treatment options. Sacituzumab govitecan (SG) is a novel antibody-drug conjugate. It consists of a monoclonal antibody targeting Trop-2, an epithelial cell surface antigen overexpressed in UC, conjugated to the active metabolite of irinotecan (SN38). Methods: We performed a phase I/II basket study in pts with advanced solid tumors receiving intravenous SG administered on day 1 and 8 of 21-day cycles, until progression or unacceptable toxicity. CT/MRI scans were obtained at 8-week intervals for response assessment. We evaluated pts with mUC who progressed after ≥1 prior systemic therapy and were treated with SG at the 10 mg/kg dose level. Endpoints included safety, objective response rate (ORR) by RECIST 1.1, clinical benefit rate (CBR; complete response [CR], partial response [PR], or else SD ≥6-mo), and Kaplan-Meier estimated duration of response (DOR), progression-free survival (PFS), and overall survival (OS). Results: 45 pts (41M/4F; median age 67, range 49-90; ECOG 0/1: 31%/69%) received a median of 2 (range: 1-6) prior treatment lines, including PLT-based chemotherapy (95%) and CPI (38%). 33 had visceral metastases involving liver (n=15), lung (n=27), and other organs (n=5). The ORR was 31% (14/45), with 2 CR and 12 PR. In pts with visceral involvement, the ORR was 27% (9/33). The ORR in CPI-treated pts was 23% (4/17). The median DOR was 12.6 mo (2 pts continuing >2 y), and the CBR was 47% (21/45). Median PFS and OS were 7.3 mo and 18.9 mo, respectively. The AE profile was consistent with prior reports. Grade ≥3 AEs in ≥5% of pts were neutropenia/neutrophil count decreased (38%), anemia (11%), hypophosphatemia (11%), diarrhea (9%), fatigue (9%), and febrile neutropenia (7%). Conclusions: SG demonstrated clinical activity in pts with relapsed/refractory mUC, including CPI-treated pts and pts with visceral disease. A single-arm, open-label, global phase 2 trial is underway to evaluate antitumor activity and safety of SG in advanced UC.(TROPHY-U-01; NCT03547973). Clinical trial information: NCT03547973.