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

190Background: 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 retrospective...