On May 5, 2021, the FDA accelerated the approval of the PD-1 inhibitor pembrolizumab (Keytruda; Merck & Co), in combination with trastuzumab plus fluoropyrimidine- and platinum-containing chemotherapy, for the first-line treatment of patients with locally advanced unresectable or metastatic HER2-positive gastric or gastroesophageal junction (GEJ) adenocarcinoma.
This approval was based on findings from the prespecified interim analysis of 264 patients with advanced unresectable or metastatic HER2-positive gastric or GEJ adenocarcinoma in the ongoing KEYNOTE-811 clinical trial who had not received systemic therapy for metastatic disease. This multicenter, randomized, double-blind, placebo-controlled study randomized the 264 patients in a 1:1 ratio to pembrolizumab 200 mg or to placebo every 3 weeks, in combination with trastuzumab and either fluorouracil plus cisplatin or capecitabine plus oxaliplatin.
The main efficacy measure for this analysis was the overall response rate (ORR). The ORR was 74% (95% confidence interval [CI], 66-82) in the pembrolizumab arm versus 52% (95% CI, 43-61) in the placebo arm, a significant difference (one-sided P value <.0001). The median duration of response was 10.6 months in the pembrolizumab arm versus 9.5 months in the placebo arm.
The adverse reactions reported in this study for pembrolizumab were consistent with the drug’s known safety profile.
The recommended pembrolizumab dose for these indications is 200 mg every 3 weeks or 400 mg every 6 weeks.