Merck aims for prostate cancer dominance with 3 new phase 3 Keytruda studies

Merck says it now has the largest prostate cancer development program for PD-1/PD-L1 drugs. (Merck)

If Merck & Co. gets its way, it won’t be long before the prostate cancer treatment landscape looks pretty different.

After fielding promising early results for immuno-oncology star Keytruda in metastatic, castration-resistant forms of the disease, the New Jersey drugmaker is adding a trio of late-stage studies to its Keytruda program, hoping they'll deliver some combo approvals.

Merck will run phase 3 studies testing its standout drug in tandem with Lynparza, the PARP inhibitor it shares with AstraZeneca; in a cocktail containing the chemotherapy docetaxel and steroid prednisone; and alongside Xtandi, a hot prostate cancer drug from Pfizer and Astellas.

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The move comes on the back of positive data from the phase 1b/2 Keynote-365 trial that Merck trotted out Thursday morning. In the cohort of patients receiving the Keytruda-Lynparza duo, 12% recorded a decrease of 50% or more in prostatic specific antigen, a protein whose levels are often elevated in men with prostate cancer. The Keytruda-docetaxel-prednisone regimen produced a PSA response rate of 31%, while the Keytruda-Xtandi posted a rate of 26%.

RELATED: AstraZeneca pioneer Lynparza scores with Zytiga combo in prostate cancer

In each of the groups, at the six-month mark, more than 70% of patients had survived, and in the docetaxel-prednisone and Xtandi groups, more than 90% of patients were still alive.

Of course, Merck isn’t the only company that’s testing its PD-1/PD-L1 drug in prostate cancer—or its PARP inhibitor, for that matter. In 2017, archrival Bristol-Myers Squibb teamed up with PARP drugmaker Clovis Oncology for a phase two prostate cancer test of Opdivo and Rubraca, and BMS has Opdivo going in a number of other prostate cancer trials, too.

RELATED: With Clovis team-up, Bristol-Myers' Opdivo eyes dynamic-duo attack on a trio of cancers

And Thursday, Johnson & Johnson trumpeted phase 2 data showing that Zejula—the third major player in the PARP class, and a drug to which it owns the rights in prostate cancer—could provoke a response in about 40% of mCRPC patients with BRCA mutations.

But Merck is aiming to show up its rivals. The addition of the three new studies will give it the largest development program with a PD-1/PD-L1 drug in prostate cancer, and it’ll also make it the only drugmaker to feature overall survival—considered the gold standard in cancer trials—as a coprimary endpoint through phase 3 trials.

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