Pembrolizumab versus placebo as adjuvant therapy in resected stage IIB or IIC melanoma: Long-term follow-up, crossover, and rechallenge with pembrolizumab in the phase III KEYNOTE-716 study

Background: Adjuvant pembrolizumab prolonged recurrence-free survival (RFS) and distant metastasis-free survival (DMFS) in patients with resected stage IIB/IIC melanoma in KEYNOTE-716. Results of a post hoc 4-year analysis are reported, including progression/recurrence-free survival 2 (PRFS2). Methods: Patients were randomly assigned 1:1 to pembrolizumab 200 mg or placebo intravenously every 3 weeks (part 1). RFS was the primary end point; DMFS was secondary. Patients with recurrence following placebo or 17 cycles of pembrolizumab could cross over to or be rechallenged with pembrolizumab (part 2). Results: Median follow-up (n = 976) was 52.8 months (range, 39.4–64.8). RFS (HR, 0.62 [95 % CI, 0.50–0.78]) and DMFS (HR, 0.59 [0.45–0.77]) favored pembrolizumab. At 48 months, RFS rates were 71.3 % for pembrolizumab and 58.3 % for placebo, and DMFS rates were 81.0 % and 70.1 %, respectively. The HR for PRFS2 was 0.75 (95 % CI, 0.56–1.01); 48-month PRFS2 rates were 82.5 % for pembrolizumab and 76.7 % for placebo. In the crossover population, median follow-up was 36.9 months; median RFS was not reached (NR; 95 % CI, 16.8-NR; 48-month RFS, 50.6 %) in patients with resectable disease (n = 41) and median progression-free survival was 22.0 months (4.5-NR) in patients with unresectable disease (n = 30). Among patients rechallenged, median follow-up was 21.9 months; none with resectable disease had recurrence (n = 6) and 1 with unresectable disease had best response of stable disease (n = 3). No new safety signals were observed. Conclusions: With > 4 years follow-up, pembrolizumab continued to prolong RFS and DMFS and had antitumor activity in patients who crossed over to pembrolizumab.