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Merck Nets Confirmatory Data on Keytruda, Herceptin, Chemo Combo in HER2-Positive Gastric Cancer

NEW YORK – Merck said Wednesday that its Phase III KEYNOTE-811 trial met its primary endpoint by showing that the addition of its checkpoint inhibitor Keytruda (pembrolizumab) to Genentech's anti-HER2 therapy Herceptin (trastuzumab) and chemotherapy significantly extended overall survival when given as a first-line treatment to patients with HER2-positive, locally advanced, unresectable or metastatic gastric or gastroesophageal junction cancer.

Merck will share the full results from the trial with regulatory authorities worldwide.

The US Food and Drug Administration granted accelerated approval to Keytruda plus Herceptin and chemo in this setting in 2021 based on earlier results from the KEYNOTE-811 trial showing that Keytruda-Herceptin-chemo improved response rates and duration of response compared to Herceptin-chemo. Then, in 2023, the FDA limited the regimen's indication to only HER2-postive gastric or gastroesophageal junction cancer patients whose tumors express PD-L1 with a combined positive score (CPS) greater than or equal to one.

Now, according to Merck, the final analysis of the KEYNOTE-811 trial has demonstrated a statistically significant and clinically meaningful improvement in overall survival in the intent-to-treat population with Keytruda-Herceptin-chemo compared to Herceptin-chemo. The greatest benefit, however, was seen in the PD-L1-positive subset in which the regimen is currently approved.

The final overall survival and progression-free survival data readout from KEYNOTE-811 is the confirmatory data the firm needs to convert this combination's accelerated approval to full approval. Merck will present the full results from KEYNOTE-811 at an upcoming medical meeting.

In Europe, the Keytruda-Herceptin-chemo combination was also approved in 2023 as a first-line treatment for HER2-positive advanced gastric and gastroesophageal cancer patients whose tumors express PD-L1.