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Merck KGaA on Cancer Vaccines: We're Not Crazy, Just Convinced

Merck KGaA claims they aren't crazy for initiating a Phase III breast cancer trial with the therapeutic cancer vaccine Stimuvax -- they're just completely convinced the darn thing is going to work.

I questioned the sanity of the German pharma's trial initiation last month because Stimuvax 1) hasn't been vetted in a Phase II breast cancer trial, 2) failed its Phase II lung cancer trial, and 3) is only about a year away from de-risking itself a bit with interim data from a Phase III lung cancer trial.

Oliver Kisker, Merck's vice president of global clinical development for the oncology unit, defended his firm's decision.

As to the lack of Phase II experience in breast cancer, Kisker noted that Stimuvax targets MUC1, a protein that promotes tumor growth and survival and is overexpressed in several types of cancer, including both lung and breast. If the target worked in lung cancer, it should work in breast cancer, too.

Of course, that rationale didn't pan out so well for ImClone Systems (now part of Eli Lilly): EGFR is overexpressed in prostate, breast, pancreatic, lung, colorectal, head/neck and other cancers, yet EGFR-targeted antibody Erbitux (cetuximab) is approved for both colorectal and head/neck cancers but has suffered setbacks in pancreatic cancer trials.

Kisker said the two situations are completely different, since Erbitux is an antibody and Stimuvax is a vaccine. He should know: Merck KGaA is the overseas partner for Erbitux.

On to point No. 2 -- Stimuvax's only randomized Phase II trial failed to meet its primary endpoint of improving survival. Yet Kisker said what's really important is the data from a pre-stratified yet retrospective subset analysis of earlier-stage patients, which showed median survival of 30.6 months with the vaccine compared to 13.3 months with placebo. The overall trial had too few patients and was "never expected" to improve survival, Kisker said, but the subset analysis provides the rationale for the ongoing Phase III lung cancer trial.

The first interim analysis from that Phase III lung cancer trial is expected in about a year, so why didn't Merck wait for those data before jumping into an expensive Phase III breast cancer trial? "The most important question for us is, do we believe in the Phase II data? We believe that we do have proof of concept," Kisker said.

In for a penny, in for a pound indeed!

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