Why GlaxoSmithKline's positive trial news matters

When GlaxoSmithKline bought Tesaro for $5 billion last December, one of management’s big arguments in favor of the deal was that the company's lead drug, Zejula, would be useful in many more cancers than investors expected. Zejula inhibits a protein called PARP, which is involved in repairing DNA. So far, it has proved useful mainly in cancers that are caused by mutations in the BRCA gene, the same one that causes breast and ovarian cancer. But GSK argued that there are cancers where Zejula would work in a larger group of patients.

At the time, STAT's Matthew Herper peppered GSK with questions on the reasons for its confidence. Were there other trials that would prove the company's case? Did GSK have data from its genomics efforts, which it had been talking up, that others didn't have? What made this worth a $5 billion bet?

The most important of those studies, GSK Chief Scientific Officer Hal Barron said, was one called PRIMA, which would test whether using Zejula in front-line ovarian cancer, before other drugs, would slow the cancer's progress in patients who tested positive for homologous recombination defect, or HRD.

On Monday, GSK announced that this ovarian study was positive not only in ovarian cancer patients with BRCA mutations, or who tested positive for HRD, but in the entire group as well.

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