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Only 12% of patients with advanced kidney cancer survive five years or more. Exelixis (NASDAQ:EXEL) hopes to increase that number, and based on its latest clinical trial results, the small biotech appears to be on the right track. That's great news for kidney cancer patients. But Exelixis' great news could present a big threat for Pfizer (NYSE:PFE) and Bristol-Myers Squibb (NYSE:BMY).

CABOSUN shines

On Oct. 10, Exelixis announced results from its phase 2 CABOSUN study of Cabometyx in patients with previously untreated advanced kidney cancer. This clinical trial was structured as a head-to-head comparison between Cabometyx and Pfizer's Sutent, and Cabometyx emerged as the clear winner.

The median progression-free survival for patients taking Exelixis' drug was 8.2 months compared to 5.6 months for patients taking Sutent. Nearly half (46%) of patients who were given Cabometyx were either completely cleared of cancer or had tumors shrink significantly. For patients who took Sutent, the objective response rate was only 18%. 

What about safety? The two drugs seemed to be about even. Nearly all of the patients who took either one experienced at least one adverse event. Side effects for patients in both arms of the study included hypertension, diarrhea, and fatigue. Three of the patients who were administered Cabometyx experienced grade 5 (most serious) adverse events (acute kidney injury, sepsis, and gastrointestinal perforation). Two of the patients taking Sutent experienced grade 5 adverse events (sepsis and vascular disorder).

Overall, the results were so impressive that Exelixis now plans to submit a Supplemental New Drug Application (sNDA) for Cabometyx as a first-line treatment for advanced kidney cancer. The drug received regulatory approval in the U.S. and Europe earlier this year as a second-line treatment for advanced kidney cancer.

Potential ripple impact

Right now, Sutent is the standard of care in fighting kidney cancer. Pfizer made $1.12 billion from the drug in 2015, and sales in the first half of 2016 were up 10% year over year. It should be noted, though, that these figures include sales for two other indications for which the drug is approved -- gastrointestinal stromal tumor and a type of pancreatic cancer.Exelixis should be in good position to take away a chunk of Pfizer's market share if Cabometyx wins approval.

Pfizer isn't the only Big Pharma company that could see its revenues threatened by the biotech, though.

Bristol-Myers Squibb gained FDA approval in late 2015 for Opdivo to be used as a second-line treatment for advanced kidney cancer. The drugmaker also has a phase 3 study in progress testing Opdivo and Yervoy as a first-line advanced kidney cancer treatment. Like Exelixis' CABOSUN study, Bristol's late-stage trial pits its regimen against Sutent.

Bristol's study isn't scheduled to wrap up until 2019. However, Exelixis will have a head start if Cabometyx is approved as a first-line treatment for kidney cancer. Therefore, the Opdivo regimen will probably need to outperform Sutent by more than Cabometyx did to be as successful as Bristol hopes it will be.

Pfizer and Bristol-Myers Squibb should both feel at least a little threatened by Exelixis' great results with Cabometyx. However, neither of the two big drugmakers will be hurt too badly if Exelixis' drug gains approval and does as well as expected. Both Sutent and Opdivo are approved for multiple indications (with possibly more on the way). And, unlike Exelixis, Pfizer and Bristol both have large product lineups and pipelines that help insulate them from the occasional threat that crops up to the sales of individual drugs.  

 

Keith Speights has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Exelixis. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.