Merck halts prostate cancer study while reporting positive readout in biliary tract cancer

Merck is slamming the brakes on a late-stage Keytruda study in prostate cancer after an interim analysis showed no improvement in survival, the company announced on Wednesday. However, the pharma giant cushioned the blow with a positive look at a separate study in biliary tract cancer.

An independent data monitoring committee reviewing the Phase III KEYNOTE-991 trial saw no improvement in overall survival or radiographic progression-free survival in a Keytruda combination group compared to the control group, Merck said in a news release. The trial was conducted in more than 1,200 patients with metastatic hormone-sensitive prostate cancer (mHSPC), or those whose cancer is controlled by keeping testosterone levels as low as would be expected after castration.

Researchers paired Keytruda with enzalutamide, sold by Astellas and Pfizer under the brand name Xtandi, and androgen deprivation therapy (ADT), while control patients received a placebo in combination with enzalutamide and ADT. The study wasn’t slated for completion until 2026, according to a federal register of clinical trials.

In addition to failing the primary endpoints, the Keytruda combo group experienced a greater amount of serious adverse events, according to the news release.

“Merck is informing study investigators of the decision and advises patients in the study to speak to their physician regarding treatment,” the company said.

The news comes on the heels of Keytruda’s late-stage fail in metastatic castration-resistant prostate cancer (mCRPC) back in August. More than 1,000 patients with mCRPC who did not respond to hormone therapy enrolled in the trial, dubbed KEYNOTE-921. However, Keytruda alongside chemotherapy failed to best chemotherapy alone in both overall and progression-free survival.

Scientists continue to test Keytruda in a handful of studies for mCRPC patients, Merck said on Wednesday.

Meanwhile, the Big Pharma unveiled some positive results from a final analysis of its KEYNOTE-966 trial in advanced or unresectable biliary tract cancer (BTC), lining up a rivalry with AstraZeneca’s Imfinzi.

Eliav Barr

First-line patients who took Keytruda along with standard-of-care chemotherapy saw a statistically significant change in overall survival compared to those who took only chemo, according to Merck. While the company has yet to show the hard numbers, Merck Research Laboratories’ senior VP, head of clinical development and CMO Eliav Barr said in a news release that the company is “very encouraged” by the results.

“Biliary tract cancer is typically diagnosed at an advanced stage, and these patients face a poor prognosis, with five-year survival rates estimated to be approximately 5% to 15%,” he said.

AstraZeneca’s PD-L1 blockbuster Imfinzi beat Keytruda across the finish line in this setting, claiming a win for advanced BTC patients back in September. The rival drug is indicated alongside the chemotherapy drugs gemcitabine and cisplatin. An estimated 25% of patients treated with Imfinzi plus chemo in a Phase III trial were still alive at two years, versus 10% treated with chemotherapy alone, according to AstraZeneca.

Merck’s stock $MRK was up by less than 1% on Wednesday, trading at around $109.41 per share.

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