Merck & Co.'s Keytruda fails late-stage study as second-line treatment for gastric cancer

Merck & Co. announced that a pivotal Phase III study of Keytruda (pembrolizumab) as a second-line treatment for patients with advanced gastric or gastroesophageal junction (GEJ) adenocarcinoma failed to meet its primary endpoint of overall survival (OS) in patients whose tumours expressed PD-L1. The company added that in the KEYNOTE-061 trial, progression-free survival (PFS) in the PD-L1 positive population did not show statistical significance.

In September, the FDA cleared Keytruda as a third-line treatment for previously treated patients with recurrent locally advanced or metastatic gastric or GEJ cancer whose tumours express PD-L1, with disease progression on or after two or more prior lines of therapy including fluoropyrimidine- and platinum-containing chemotherapy and if appropriate, HER2/neu-targeted therapy. The accelerated approval is based on tumour response rate and durability of response.

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The KEYNOTE-061 study randomised 592 patients with advanced gastric or GEJ adenocarcinoma whose disease progressed after first-line treatment with platinum and fluoropyrimidine doublet therapy to receive Keytruda or paclitaxel. The trial's main goals are OS and PFS in patients whose tumors express PD-L1, while secondary endpoints include PFS, OS and overall response rate in patients regardless of PD-L1 expression.

Merck noted that the study was designed to initially evaluate efficacy in patients whose tumours expressed PD-L1, which if positive, would lead to further analysis in the overall population. "We remain committed to the continued study of Keytruda for gastric cancers," remarked Roy Baynes, chief medical officer at Merck Research Laboratories.

The company is currently studying Keytruda as a monotherapy or in combination with chemotherapy as first-line treatment for patients with PD-L1 positive advanced gastric or GEJ cancer in the Phase III KEYNOTE-062 trial, while the late-stage KEYNOTE-585 study is investigating the therapy in combination with chemotherapy in a neoadjuvant/adjuvant setting.

Last month, Merck KGaA and Pfizer announced that the anti-PD-L1 antibody Bavencio (avelumab) failed to demonstrate superior OS versus physician's choice of chemotherapy as a third-line treatment for patients with unresectable, recurrent or metastatic gastric cancer, missing the primary endpoint of a Phase III study. For related analysis, see ViewPoints: Bavencio’s failure in 3L gastric cancer fuels speculation in battle of PD-1 versus PD-L1.

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