PURPOSE: Pembrolizumab demonstrated durable antitumor activity in patients with previously treated, advanced microsatellite instability–high or mismatch repair–deficient (MSI-H/dMMR) tumors, including endometrial cancer, in the nonrandomized, open-label, multicohort, phase II KEYNOTE-158 study ( NCT02628067 ). We report efficacy and safety outcomes for patients with MSI-H/dMMR endometrial cancer enrolled in KEYNOTE-158. METHODS: Eligible patients from cohorts D (endometrial cancer, regardless of MSI-H/dMMR status) and K (any MSI-H/dMMR solid tumor, except colorectal) with previously treated, advanced MSI-H/dMMR endometrial cancer received pembrolizumab 200 mg once every 3 weeks for 35 cycles. The primary end point was objective response rate per RECIST version 1.1 by independent central radiologic review. Secondary end points included duration of response, progression-free survival, overall survival, and safety. RESULTS: As of October 5, 2020, 18 of 90 treated patients (20%) had completed 35 cycles of pembrolizumab and 52 (58%) had discontinued treatment. In the efficacy population (patients who received ≥ 1 dose of pembrolizumab and had ≥ 26 weeks of follow-up; N = 79), the median time from first dose to data cutoff was 42.6 (range, 6.4-56.1) months. The objective response rate was 48% (95% CI, 37 to 60), and median duration of response was not reached (2.9-49.7+ months). Median progression-free survival was 13.1 (95% CI, 4.3 to 34.4) months, and median overall survival was not reached (95% CI, 27.2 months to not reached). Among all treated patients, 76% had ≥ 1 treatment-related adverse event (grades 3-4, 12%). There were no fatal treatment-related events. Immune-mediated adverse events or infusion reactions occurred in 28% of patients (grades 3-4, 7%; no fatal events). CONCLUSION: Pembrolizumab demonstrated robust and durable antitumor activity and encouraging survival outcomes with manageable toxicity in patients with previously treated, advanced MSI-H/dMMR endometrial cancer.

Importance There is a strong rationale for treating sarcomas with immunotherapy. Objective To assess the efficacy and safety of programmed cell death protein 1 (PD-1) targeting in combination with metronomic chemotherapy in sarcomas. Design, Setting, and Participants This was an open-label, multicenter, phase 2 study of 4 cohorts of patients with advanced soft-tissue sarcoma (STS), including leiomyosarcoma (LMS), undifferentiated pleomorphic sarcoma (UPS), other sarcomas (others), and gastrointestinal stromal tumor (GIST). All patients received 50 mg twice daily cyclophosphamide 1 week on and 1 week off and 200 mg of intravenous pembrolizumab every 3 weeks. Intervention or Exposure Pembrolizumab in combination with metronomic cyclophosphamide. Main Outcomes and Measures There was a dual primary end point, encompassing both the nonprogression and objective responses at 6 months per Response Evaluation Criteria in Solid Tumours (RECIST) v1.1 for LMS, UPS, and others and 6-month nonprogression for GIST. An objective response rate of 20% and/or a 6-month nonprogression rate of 60% were determined as reasonable objectives for treatment with meaningful effect. Correlative studies of immune biomarkers were planned from patient tumor and plasma samples. Results Between June 2015 and July 2016, 57 patients were included (median [range] age, 59.5 [18.5-84.0] years; 24 women [42%]); 50 patients were assessable for the efficacy end point. Three patients experienced tumor shrinkage, resulting in a partial response in a single solitary fibrous tumor. The 6-month nonprogression rates were 0%, 0%, 14.3% (95% CI, 1.8%-42.8%) for LMS, UPS, and others, respectively, and 11.1% (95% CI, 2.8%-48.3%) for GIST. The most frequent adverse events were grade 1 or 2 fatigue, diarrhea, and anemia. The only patient who experienced partial response was the only one with strong programmed cell death 1 ligand 1–positive staining in immune cell. Strong infiltration by macrophage expressing the inhibitory enzyme indoleamine 2,3-dioxygenase 1 (IDO1) was observed in the majority of cases. Moreover, a significant increase in the kynurenine to tryptophan ratio was observed in patient plasma samples during the study treatment. Conclusions and Relevance We found that PD-1 inhibition has limited activity in selected STS and GIST. This may be explained by an immunosuppressive tumor microenvironment resulting from macrophage infiltration and IDO1 pathway activation. Trial Registration clinicaltrials.gov Identifier:NCT02406781

BRAFV600E alterations are prevalent across multiple tumors. Here we present final efficacy and safety results of a phase 2 basket trial of dabrafenib (BRAF kinase inhibitor) plus trametinib (MEK inhibitor) in eight cohorts of patients with BRAFV600E-mutated advanced rare cancers: anaplastic thyroid carcinoma (n = 36), biliary tract cancer (n = 43), gastrointestinal stromal tumor (n = 1), adenocarcinoma of the small intestine (n = 3), low-grade glioma (n = 13), high-grade glioma (n = 45), hairy cell leukemia (n = 55) and multiple myeloma (n = 19). The primary endpoint of investigator-assessed overall response rate in these cohorts was 56%, 53%, 0%, 67%, 54%, 33%, 89% and 50%, respectively. Secondary endpoints were median duration of response (DoR), progression-free survival (PFS), overall survival (OS) and safety. Median DoR was 14.4 months, 8.9 months, not reached, 7.7 months, not reached, 31.2 months, not reached and 11.1 months, respectively. Median PFS was 6.7 months, 9.0 months, not reached, not evaluable, 9.5 months, 5.5 months, not evaluable and 6.3 months, respectively. Median OS was 14.5 months, 13.5 months, not reached, 21.8 months, not evaluable, 17.6 months, not evaluable and 33.9 months, respectively. The most frequent (≥20% of patients) treatment-related adverse events were pyrexia (40.8%), fatigue (25.7%), chills (25.7%), nausea (23.8%) and rash (20.4%). The encouraging tumor-agnostic activity of dabrafenib plus trametinib suggests that this could be a promising treatment approach for some patients with BRAFV600E-mutated advanced rare cancers. ClinicalTrials.gov registration: NCT02034110.