On Nov. 7, 2023, the FDA revised the existing indication of pembrolizumab (Keytruda, Merck) with trastuzumab-, 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 updated indication, which remains approved under accelerated approval regulations, restricts its use to patients whose tumors express programmed death ligand-1 (PD-L1) (combined positive score [CPS] ≥1) as determined by an FDA-approved test. The FDA also approved the Agilent PD-L1 IHC 22C3 pharmDx as a companion diagnostic device to selected patients with gastric or GEJ adenocarcinoma whose tumors express PD-L1 (CPS ≥1).


Efficacy was evaluated in KEYNOTE-811, a multicenter, randomized, double-blind, placebo-controlled trial in patients with HER2-positive locally advanced or metastatic gastric or GEJ adenocarcinoma who have not previously received systemic therapy for metastatic disease. Patients were randomized (1:1) to receive pembrolizumab 200 mg intravenously or placebo every two weeks with trastuzumab and either 5-fluorouracil plus cisplatin or capecitabine plus oxaliplatin.

The major efficacy outcomes of KEYNOTE-811 are overall survival (OS) and progression-free survival (PFS). The May 5, 2021, approval was based on an interim analysis of objective response rate (ORR) and duration of response (DOR). At that time, ORR and DOR were assessed in the first 264 patients who were randomized. ORR was 74% (95% CI, 66%-82%) in the pembrolizumab plus chemotherapy arm and 52% (95% CI, 43%-61%) in the placebo plus chemotherapy arm (P<0.0001). Median DOR was 10.6 months (range, 1.1+ to 16.5+ months) and 9.5 months (range, 1.4+ to 15.4+ months) in the respective arms.

In a recent, prespecified interim analysis of the fully enrolled trial (n=698), in a subgroup analysis conducted in patients with PD-L1 (CPS <1; n=104), the hazard ratios for OS and PFS were 1.41 (95% CI, 0.90-2.20) and 1.03 (95% CI, 0.65-1.64), respectively.

The safety profile for participants treated with pembrolizumab and trastuzumab plus chemotherapy in KEYNOTE-811 was generally consistent with the known safety profiles of either trastuzumab plus chemotherapy alone or pembrolizumab monotherapy.

View the full prescribing information for pembrolizumab.


—GEN Staff

Based on a press release from the FDA.