SOUTH SAN FRANCISCO, Calif. (TheStreet) -- The Exelixis (EXEL) - Get Exelixis, Inc. Report cancer drug Cometriq scored a decisive, much-needed victory in a late-stage trial of kidney cancer patients, setting the stage for an expanded approval next year and a significant bump in commercial sales.

In the phase III study known as "METEOR," Cometriq achieved the primary endpoint of delaying tumor progression or death compared to the Novartis (NVS) - Get Novartis AG Sponsored ADR Report drug Afinitor, Exelixis said Monday. The study enrolled patients with metastatic kidney cancer previously treated with at least one VEGF-targeted drug, such as Pfizer's (PFE) - Get Pfizer Inc. Report Sutent.

Cometriq also demonstrated a strong trend toward prolonging survival compared to Afinitor, although the analysis was still too immature to reach statistical significance.

Exelixis plans to submit the METEOR kidney cancer data for approval in the U.S. and Europe in early 2016.

Cometriq is approved as a treatment for medullary thyroid cancer, but generated just $25 million in 2014 sales because the targeted patient population is so small. The positive kidney cancer results announced Monday represent the latest and best opportunity for Exelixis to boost Cometriq revenue following the disappointing failure of prostate cancer studies last year.

Exelixis says the commercial opportunity for Cometriq in kidney cancer is significant, with approximately 17,000 eligible second-line patients in the U.S. and 37,000 patients globally. In 2014, Novartis' Afinitor sales for kidney cancer totaled a bit more than $400 million, Exelixis estimates.

The METEOR study randomized 658 second-line kidney cancer patients to treatment with Cometriq or Afinitor. At the time of the primary analysis, Cometriq reduced the risk of tumor progression or death (progression-free survival) by 42% compared to Afinitor, achieving the primary endpoint with statistical significance.

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Cometriq benefited kidney cancer patients more than Exelixis expected based on the design of the study, which assumed the drug would reduce the risk of tumor progression or death by 33% compared to Afinitor.

On the survival analysis, Cometriq reduced the risk of death by 33% compared to Afinitor, but the difference was not statistically significant. The METEOR trial will continue and another analysis of survival will be conducted in 2016.

The frequency of serious adverse events reported in the study were "approximately balanced" between Cometriq and Afinitor, Exelixis said, without disclosing details. The rate of treatment discontinuation due to adverse events was 10% in both study arms.

Exelixis intends to present more detailed results from the METEOR study at an upcoming medical conference, the company said.

Hitting the progression-free survival, or PFS, primary endpoint with a strong trend toward a survival benefit should help Exelixis greatly when it makes the case for expanding Cometriq's approval into kidney cancer.

The FDA has used PFS as the basis for approving six of seven kidney cancer drugs. The only exception was Aveo (AVEO) - Get AVEO Pharmaceuticals, Inc. Report Oncology's tivozanib, which the FDA rejected because the PFS benefit was confounded by shorter survival. Exelixis doesn't have a Special Protocol Assessment for the METEOR study, but the company says the trial design and endpoints were "discussed" with regulators in the U.S. and Europe.

Exelixis is conducting additional clinical trials of Cometriq in first-line kidney cancer and liver cancer. The company is also waiting on the FDA approval decision, expected Nov. 11, for the skin cancer drug cobimetinib, which is being developed under a partnership with Roche/Genentech (RHHBY) .

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.