PFE - Merck Keytruda combo fails lung cancer trial sees another setback in prostate cancer

Merck ( NYSE: MRK ) is discontinuing a phase 3 trial of a Keytruda combination treatment for prostate cancer after the study failed its main goals, while another late stage trial of the blockbuster drug did not meet its main objectives to treat a type of lung cancer.

Prostate cancer trial:

The phase 3 trial, dubbed KEYNOTE-641, was evaluating Keytruda  in combination with enzalutamide — sold as Xtandi by Pfizer ( PFE ) and Astellas Pharma ( OTCPK:ALPMF ) ( OTCPK:ALPMY ) — and androgen deprivation therapy (ADT) versus placebo in combination with Xtandi plus ADT to treat patients with metastatic castration-resistant prostate cancer (mCRPC).

These patients had not received chemotherapy for mCRPC, are abiraterone-naïve or are intolerant to or progressed on abiraterone acetate.

The trial enrolled about 1,240 patients.

Merck said that at an interim analysis, the Keytruda combo did not show an improvement in radiographic progression-free survival (rPFS) or overall survival (OS), the trial's dual main goals, compared to the placebo combo, and crossed a pre-specified futility boundary for OS.

PFS is the length of time during/after treatment a patient lives with the disease without it getting worse.

The pharma giant noted that in the study, the Keytruda combination was associated with a higher incidence of Grade 3-5 adverse events and serious adverse events, compared to the control group.

Merck added that based on the recommendation of an independent Data Monitoring Committee the company is discontinuing the study.

Merck said it is informing study investigators of the decision and advises patients in the trial to speak to their physician regarding treatment.

This a second setback for Merck in prostrate cancer this year, after a study called KEYNOTE-991, evaluating similar Keytruda combo failed and the company decided to stop the trial.

Non-small cell lung cancer (NSCLC) trial:

The phase 3 trial called KEYNOTE-789 was evaluating Keytruda in combination with pemetrexed (sold as Alimta among other names) plus platinum-based chemotherapy, compared to pemetrexed plus platinum-based chemotherapy to treat  patients with with metastatic NSCLC, with epidermal growth factor receptor (EGFR)-genomic tumor mutations.

These patients have previously progressed on a tyrosine kinase inhibitor (TKI) therapy, including osimertinib, marketed as Tagrisso by AstraZeneca ( AZN ).

Merck said that at final analysis, there was an improvement in OS for patients on the Keytruda combo compared to those on pemetrexed and platinum-based chemo.

However, these results did not meet statistical significance. At an earlier interim analysis, the study's other dual main goal — progression-free survival (PFS) was tested and showed an improvement in the Keytruda group compared to chemo alone, but the results did not reach statistical significance, according to the company.

The study had enrolled 492 patients.

Merck said that in both studies the safety profile of Keytruda was consistent with previously reported studies and no new safety signals were seen.

"Science is rarely a straight line, and while we are disappointed in these study results, our research to investigate KEYTRUDA in many difficult-to-treat types of cancer continues in earnest," said Eliav Barr, senior vice president and head of global clinical development, chief medical officer, Merck Research Laboratories.

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