Few advancements in treating limited-stage SCLC (LS-SCLC) have been made in decades. We report here a phase 1/2 trial of concurrent chemoradiotherapy (CRT) and pembrolizumab.

This single-center, open-label phase 1/2 study recruited adults with LS-SCLC or other neuroendocrine tumors and good performance status (Eastern Cooperative Oncology Group ≤ 2). The primary end point was safety, as assessed by dose-limiting toxicities. Concurrent CRT consisted of etoposide and a platin with 45 Gy radiotherapy (30 twice daily). Prophylactic cranial irradiation (25 Gy, 10 fractions) was given at the physician's discretion. Pembrolizumab was started concurrently with CRT and continued for up to 16 cycles. The phase 1 portion consisted of a 3 + 3 design. Toxicity was assessed with Common Terminology Criteria for Adverse Events version 4.0. Secondary outcomes were progression-free survival, overall survival, and tumor response as measured by the immune-related response criteria.

A total of 45 patients were screened, and 40 were enrolled. All completed radiation therapy and received greater than or equal to one cycle of pembrolizumab. A total of 27 (61%) received percutaneous coronary intervention. One dose-limiting toxicity was observed in the phase 1 portion. There were no grade 5 toxicities, but there were three grade 4 events (two neutropenia, one respiratory failure). Pneumonitis rate was 15% (three grade 2 and three grade 3). All 17 esophagitis events (42.5%) were grades 1 to 2. At median follow-up time of 23.1 months, the median progression-free survival time was 19.7 months (95% confidence interval: 8.8‒30.5) and the median overall survival time was 39.5 months (95% confidence interval: 8.0‒71.0).

Concurrent CRT and pembrolizumab for LS-SCLC was well tolerated and yielded favorable outcomes, providing a basis for randomized studies.