Merck's PD-1 star Keytruda shines at ASH, but lags behind Bristol-Myers' rival

Merck's new PD-1 cancer drug Keytruda (pembrolizumab) has posted another round of positive early-stage results that help demonstrate its potential in an important cancer R&D arena: hematology. But some of the biggest players and punters in the immuno-oncology field may be left wondering if Merck's ($MRK) top therapeutic hopeful is losing market ground to Bristol-Myers Squibb's ($BMY) rival treatment.

Merck showed up at the American Society of Hematology meeting in San Francisco determined to once again showcase a drug that has been capturing the attention of the entire oncology R&D field. And it pushed beyond its initial success in solid tumors into classical Hodgkin lymphoma, underscoring its wide impact on a range of cancers--particularly with upcoming combination studies in the works.

Among a group of very advanced patients who had failed standard therapies, the drug spurred a 66% overall response rate in preliminary results, with about 9 of 10 responses ongoing, making it too early to establish the median duration of response--exactly the kind of durability that the company wants to see at this stage. A complete response was seen in 21% of patients.

Merck's Eric Rubin

"This type of effect in the cancer field is unprecedented," says Eric Rubin, the vice president of clinical oncology for Merck, who says he was skeptical 5 or 6 years ago that PD-1 and PD-L1 in immuno-oncology would be the game-changing area that it is today. Not only are there clear signs of efficacy for hematological malignancies, the safety profile is clean of any unusual or unexpected outcomes.

"This is the seventh cancer type where we have presented data," adds Rubin. "And I think it is remarkable that one mechanism is showing such efficacy across the board."

Keytruda, though, isn't being developed in a vacuum, and analysts are likely to wonder whether Bristol-Myers' Opdivo could start breaking away from Merck's drug with better efficacy results. Bristol has achieved an 87% response rate in an early Hodgkin lymphoma study of its own--though Rubin notes that these small early studies involve such a small group of patients they can produce statistical differences that aren't necessarily significant in the long run. Differences in patient selection and prior treatment could also all influence outcomes and have to be taken into consideration. The final data from registration studies, which are expected to launch in the "very near future," will be the most important distinguishing factor, says Rubin.

For Bristol-Myers' Opdivo (nivolumab, the 87% response rate broke down into a 17% complete response rate with 70% achieving a partial response. 13% experienced stable disease. "Of the patients who achieved a complete and partial response, 60% (n=12) had their first response within eight weeks (range: 3-39 weeks)," investigators reported. "Data from the study also showed a progression-free survival rate of 86% at 24 weeks, meaning patients lived six months longer without their disease worsening."

Both of these drugs, along with similar programs at Roche ($RHHBY) and AstraZeneca ($AZN), represent the cutting edge of a new wave of drugs that can finally start to unleash a major immune response to cancer for many patients. It's a natural combinatorial approach that is producing significant gains for patients, and Merck currently has a program that involves more than 30 cancer types. And as Rubin notes, the FDA has kept an open-door in place at the agency to help accelerate new drug approvals in immuno-oncology.