Merck gets Canadian nod for Keytruda in combo with fluoropyrimidine- and platinum-containing-chemotherapy for HER2-negative gastric or gastroesophageal junction adenocarcinoma

“We are proud of the recent expansion of KEYTRUDA‘s indications in gastric cancers, which often go undetected until an advanced stage, at which point patients face a poor prognosis,” says André Galarneau, PhD, Executive Director & Vice President, Oncology Business Unit at Merck Canada. “This milestone underscores our commitment to helping improve the lives of patients by offering treatment options that can lead to better health outcomes.”

KEYNOTE-859 was a multicenter, randomized, double-blind, placebo-controlled Phase 3 trial (ClinicalTrials.gov NCT03675737) evaluating pembrolizumab in combination with fluoropyrimidine- and platinum-containing chemotherapy for the first-line treatment of locally advanced unresectable or metastatic HER2-negative gastric or GEJ adenocarcinoma. The primary endpoint was overall survival (OS) with progression-free survival (PFS) and objective response rate (ORR) included as secondary endpoints as assessed by blinded independent central review (BICR) using RECIST v1.1 modified to follow a maximum of 10 target lesions and a maximum of 5 target lesions per organ.

The trial enrolled 1579 patients who had not previously received systemic therapy for metastatic disease and were randomized 1:1 to receive pembrolizumab (200 mg every three weeks) in combination with fluoropyrimidine- and platinum-containing chemotherapy (n=790), or placebo in combination with chemotherapy (n=789). All patients received investigator’s choice of chemotherapy (5-fluorouracil plus cisplatin [FP] or capecitabine plus oxaliplatin [CAPOX]). All study medications, except oral capecitabine, were administered as an intravenous infusion for every 3-week cycle. Platinum agents could be administered for 6 or more cycles following local guidelines. Treatment continued until RECIST v1.1-defined progression of disease as determined by BICR, unacceptable toxicity, or a maximum of 24 months.

A statistically significant improvement in OS, PFS and ORR was demonstrated in patients randomized to pembrolizumab in combination with chemotherapy compared with placebo in combination with chemotherapy at the pre-specified interim analysis of OS. In the study, there was a 22% reduction in the risk of death with pembrolizumab plus chemotherapy (HR=0.78 [95% CI, 0.70-0.87]; p<0.0001) versus chemotherapy alone. The median OS for patients receiving pembrolizumab plus chemotherapy was 12.9 months (95% CI, 11.9-14.0) versus 11.5 months (95% CI, 10.6-12.1) for those receiving chemotherapy alone.

A positive association was observed between PD-L1 CPS score and the magnitude of the treatment benefit. The median duration of exposure to pembrolizumab was 6.2 months (range, 1 day to 33.7 months).

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