Update: This morning, Bristol-Myers Squibb announced that its immunotherapy, Opdivo, also delayed cancer progression more than Afinitor in kidney cancer. This raises questions about the sales potential of Exelixis’ drug.

On September 2, 2014, shares in Exelixis, a drug maker that has spent two decades trying to turn the early fruits of genetic research into drugs, plunged 48% as it announced that its cancer drug, Cometriq, did not extend survival in patients with advanced prostate cancer that had spread to their bones.

Cometriq is approved for medullary thyroid cancer, but that disease is so rare that the drug is only generated $25 million last year. But this morning, Exelixis is releasing data from another clinical trial that should breathe new life into Cometriq sales: what looks like a clear benefit in kidney cancer based on early results from a 658 patient study.

Most kidney cancer patients initially are treated with Sutent, from Pfizer, or Votrient, from GlaxoSmithKline. When those drugs fail, they are given either Afinitor, made by Novartis, or Inlyta, another Pfizer drug.

The trial result being announced today compared Cometriq to Afinitor in patients who had already been failed by another drug. Patients who got Cometriq were 42% less likely to die or have their cancer worsen than those who got Afinitor. (Cancer researchers express this as a ‘hazard ratio’ of 0.58.)

The data were released early – only 375 patients in – because they were already so statistically significant. It is not certain yet whether the drug is helping patients live longer. Patients who received Cometriq were 33% less likely to die. The result was not statistically significant, because a higher bar is set for statistical significance in early analyses of trials, but it could become so before the trial finishes in 2016.

Exelixis will be filing with U.S. and European regulators to ask to sell Cometriq for kidney cancer based on this data. Analysts think that Novartis sells about $400 million worth of Afinitor in kidney cancer (that drug is approved for other cancers as well), so it is possible that an approval could eventually result in hundreds of millions of dollars in sales.

Those impressive reductions in death are still only likely to mean that Cometriq gave patients, on average, a few more months of life. Exelixis chief executive Michael Morrissey says that he’s confident that the results are “medically important.” The data, outlined via press release, will be revealed in more detail at an upcoming medical conference.

*A previous version of this story mis-stated the name of Afinitor.

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Source: Forbes