Efficacy and Safety of Pembrolizumab in Previously Treated Advanced Neuroendocrine Tumors: Results From the Phase II KEYNOTE-158 Study

Abstract

Purpose: KEYNOTE-158 (ClinicalTrials.gov identifier: NCT02628067) investigated the efficacy and safety of pembrolizumab across multiple cancers. We present results from patients with previously treated advanced well-differentiated neuroendocrine tumors (NET).

Patients and methods: Pembrolizumab 200 mg was administered every 3 weeks for 2 years or until progression, intolerable toxicity, or physician/patient decision. Tumor imaging was performed every 9 weeks for the first year and then every 12 weeks. Endpoints included objective response rate (ORR) per RECIST v1.1 by independent central radiologic review (primary) and duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety (secondary).

Results: A total of 107 patients with NETs of the lung, appendix, small intestine, colon, rectum, or pancreas were treated. Median age was 59.0 years (range, 29-80), 44.9% had ECOG performance status 1, 40.2% had received ≥3 prior therapies for advanced disease, and 15.9% had PD-L1-positive tumors (combined positive score ≥1). Median follow-up was 24.2 months (range, 0.6-33.4). ORR was 3.7% (95% CI, 1.0-9.3), with zero complete responses and four partial responses (three pancreatic and one rectal) all in patients with PD-L1-negative tumors. Median DOR was not reached, with one of four responses ongoing after ≥21 months follow-up. Median PFS was 4.1 months (95% CI, 3.5-5.4); the 6-month PFS rate was 39.3%. Median OS was 24.2 months (95% CI, 15.8-32.5). Treatment-related adverse events (AE) occurred in 75.7% of patients, 21.5% of whom had grade 3-5 AEs.

Conclusions: Pembrolizumab monotherapy showed limited antitumor activity and manageable safety in patients with previously treated advanced well-differentiated NETs.

Figure 1.

Antitumor activity of pembrolizumab in the total population. A, Time to and duration of response assessed by RECIST v1.1 per independent central review in patients whose best overall response was partial response (n = 4). The length of the bars represents the time to the last imaging assessment. *Started new anticancer therapy without progressive disease. PR, partial response. B, Best change from baseline in target lesion size assessed by RECIST v1.1 per independent central review in patients with ≥1 evaluable postbaseline imaging assessment (n = 101). C, Kaplan-Meier estimates of progression-free survival assessed by RECIST v1.1 per independent central review in the efficacy population (N = 107); D, Kaplan-Meier estimates of overall survival in the efficacy population (N = 107). PR, partial response.