Keytruda Strikes Out Again in Endometrial Cancer with Phase III Flop

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Pictured: Merck building and sign in Silicon Valley/iStock, Sundry Photography

Merck’s Keytruda swung and missed in endometrial cancer for the second time in six months. Thursday, the pharma giant announced that its bestseller flopped in a Phase III trial in high-risk disease. 

Used as an adjuvant treatment with chemotherapy, with or without radiotherapy for newly diagnosed high-risk patients, the anti-PD-1 treatment did not meet the primary endpoint of disease-free survival compared to placebo at the interim analysis. 

Keytruda already holds two approvals in specified types of endometrial cancer—in combination with Eisai’s Lenvima for advanced, inoperable endometrial carcinoma that has progressed after therapy and as a single agent in similarly diagnosed patients. Merck also has an ongoing development program testing Keytruda in combination with chemotherapy and as a single agent in specified patient populations.  

In December 2023, the Keytruda-Lenvima combination failed to improve survival in patients with advanced or recurrent endometrial carcinoma.  

That announcement came on the heels of back-to-back Keytruda flops in non-small cell lung cancer (NSCLC). In December, the company announced that combined with its experimental anti-TIGIT antibody vibostolimab, the anti-PD1 failed to improve progression free survival in NSCLC patients. The same day, a trial of Keytruda plus AstraZeneca’s Lynparza failed to elicit significant improvement in overall survival in metastatic squamous NSCLC. Then, in March, the company announced that the Lynparza combination fell short of dual primary endpoints in specific patients with metastatic non-squamous NSCLC. 

Despite the recent disappointments, Keytruda is still raking in top sales for Merck. The blockbuster immunotherapy has racked up over 30 indications since its 2014 approval in advanced melanoma patients with a BRAF mutation.   

In April, Merck reported a 20% jump in Keytruda sales for the first quarter of 2024 compared to the same period last year. The treatment brought in $6.9 billion for the quarter, accounting for nearly half of Merck’s $14 billion total pharmaceutical sales. Analysts anticipate Keytruda will top $30 billion in annual sales by 2026 before falling off the patent cliff as biosimilars hit the market as soon as 2028.   

Kate Goodwin is a freelance life science writer based in Des Moines, Iowa. She can be reached at and on LinkedIn. 

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