Pembrolizumab treatment of advanced neuroendocrine tumors: Results from the phase II KEYNOTE-158 study.

Abstract

190 Background: Data from the KEYNOTE-028 study (NCT02054806) suggested that pembrolizumab (pembro) has clinical activity in a subset of patients (pts) with heavily pretreated neuroendocrine tumors (NET). The KEYNOTE-158 study (NCT02628067) is a phase II basket study investigating the antitumor activity of pembro in 10 specific cancer types. An analysis of the 107 pts included in the NET cohort is presented. Methods: Key eligibility criteria for this cohort included well- and moderately-differentiated NET of the lung, appendix, small intestine, colon, rectum, or pancreas; progression on or intolerance to ≥ 1 line of standard therapy; ECOG PS 0 or 1; and provision of a tumor sample for biomarker analysis. Pts received pembrolizumab 200 mg Q3W for 2 y or until progression, intolerable toxicity, or physician or patient decision. Tumor imaging was performed every 9 wks for the first 12 mo, and every 12 wks thereafter. PD-L1 positivity, defined as a combined positive score (CPS) ≥ 1, was evaluated retrospectively by IHC. Primary endpoint was ORR assessed per RECIST v1.1 by independent central radiology review. Secondary endpoints included DOR, PFS, OS, and safety. Results: 107 pts were treated. Median age was 59 (range, 29-80) y, 44.9% had ECOG PS 1, and 67.3% received ≥ 2 prior therapies for advanced disease. 15.9% of enrolled pts had PD-L1+ tumors. As of the January 15, 2018 data cutoff, the median follow-up duration was 18.6 (range, 0.2-22.7) mo. ORR was 3.7% (95% CI, 1.0-9.3), with 0 CR and 4 PR (3 pancreatic and 1 gastrointestinal [unknown primary]). 61 pts had SD as best response. The 4 responses were observed in pts with PD-L1 negative tumors. Median DOR had not been reached (range, 4.1-15.9+), with 3 of 4 responses ongoing after ≥ 9 mo follow-up. Median (95% CI) PFS was 4.1 (3.5-5.4) mo, and the 6-mo PFS rate was 38.2%. Median OS (95% CI) had not been reached (18.8-not reached), and the 6-mo OS rate was 84.6%. Treatment-related AEs occurred in 75.7% of pts, and the most common was fatigue (21.5%). 20.6% of pts had treatment-related grade 3-4 AEs. Conclusions: Pembrolizumab monotherapy showed limited antitumor activity and manageable safety in pts with previously treated advanced NET. Clinical trial information: NCT02628067.