Merck's Keytruda Takes Another Hit with Phase III Prostate Cancer Fail

Merck_Smith Collection/Gado/Getty Images

Smith Collection/Gado/Getty Images

Merck's Keytruda (pembrolizumab) has taken another hit after the drug failed to meet dual primary endpoints in the Phase III KEYNOTE-921 trial for metastatic castration-resistant prostate cancer (mCRPC).

The randomized, double-blind study enrolled 1,030 patients who received either 200mg of Keytruda every three weeks for around two years plus prednisone and chemotherapy or a placebo with prednisone and chemotherapy. The participants were mCRPC patients who have not undergone chemotherapy but whose disease has progressed or are intolerant to a next-generation hormonal agent.

The two primary endpoints were overall survival (OS) and radiographic progression-free survival (rPFS). The secondary endpoints were prostate-specific antigen response rate, time to initiation of the first subsequent anti-cancer therapy, duration of response and objective response rate.

At the end of the study, although no new safety concerns were observed, Keytruda did not demonstrate significant improvements based on the pre-specified statistical plan. Full details will be shared at a future medical conference.

Keytruda is an anti-programmed death receptor-1 (PD-1) therapy that works by boosting the immune system's ability to detect and kill tumor cells. Prostate cancer is the second most common cancer in men worldwide, and 10% to 20% of patients with the advanced version are likely to develop CRPC in five years. At least 85% of these will have metastases upon CRPC diagnosis.

"Results from this study serve as an important reminder that metastatic prostate cancer remains very difficult to treat, and more research is needed. We will continue to advance our clinical development program to evaluate KEYTRUDA-based combinations and novel candidates for patients with this disease. We are grateful to the patients and investigators for their participation in this study," Dr. Eliav Barr, the senior vice president, head of global clinical development and chief medical officer of Merck Research Laboratories, said in a statement.

This disappointing news follows one month after the company announced that its Phase III trial of Keytruda for unresected, locally advanced head and neck squamous cell carcinoma (HNSCC) failed to achieve the primary endpoint of event-free survival. That same week, Merck also said it is no longer continuing its Phase III study on Lynparza for colorectal cancer.

Despite the results, Merck, known as MSD outside the United States and Canada, is not backing down on its oncology research and development activities, particularly for prostate cancer. It has several ongoing studies involving Keytruda to find a viable treatment for the said disease. These include Phase II trials KEYNOTE-199 and KEYNOTE-365 and Phase III trials KEYNOTE-641 and KEYNOTE-991.

Keytruda is approved in the U.S. for various indications, including unresectable or metastatic melanoma, relapsed or refractory classical Hodgkin lymphoma, locally advanced or metastatic urothelial carcinoma and non-muscle invasive bladder cancer, among others. There are currently over 1,600 trials studying Keytruda for various cancers and rare diseases worldwide.

Back to news