Exelixis’ fast-growing tyrosine kinase inhibitor Cabometyx just added another FDA approval. It can now treat liver cancer patients if Bayer’s Nexavar is no longer helpful, putting it in a field that’s already crowded with Bayer’s Stivarga and some checkpoint inhibitor stars.

The FDA based the new approval for Cabometyx, which already bears a green light in kidney cancer, on positive data from a phase 3 study dubbed Celestial. In that trial, Cabometyx showed it could extend patients' lives by a median 10.2 months, significantly higher than the eight months patients lived on placebo. 

"Physicians are eager for new options for these patients, and the results of the Celestial trial demonstrate that Cabometyx has the efficacy and safety profile to become an important new therapy in our efforts to slow disease progression and improve treatment outcomes," the study’s lead investigator, Ghassan Abou-Alfa, M.D., of Memorial Sloan Kettering Cancer Center, said in a statement.

However, the liver cancer arena is already filled with experienced players. There is Stivarga, which Bayer pushed on the market as a follow-up to Nexavar. However, the drug hasn’t lived up to the German drugmaker’s expectations as one of its "Big Five" crucial new drugs. Thanks to an 8.8% decline in the U.S. on a currency-adjusted basis, which Bayer attributed to "a highly competitive market," the drug only returned €229 million ($262 million) in global sales through the first nine months of 2018.

More serious competition could come from two PD-1 blockbusters, Bristol-Myers Squibb’s Opdivo and Merck & Co.’s Keytruda. Opdivo earned its second-line liver cancer nod in September 2017, and Keytruda followed just last November. While neither drug has come up with overall survival data, their response rates—18.2% for Opdivo and 17% for Keytruda—look superior to Cabometyx’s 4%, even though these are separate trials not meant for head-to-head comparisons.

Cabometyx is the backbone of Exelixis’ portfolio, enjoying fast growth especially after earning an early FDA nod in first-line kidney cancer in December 2017. During the third quarter, Cabometyx product revenue—as opposed to collaboration revenue from Exelixis' Ipsen partnership—jumped 12% over the previous quarter, to about $158 million. Demand grew by more than 5% and the prescriber base expanded by about 11%, the company’s commercial leader, P.J. Haley, said on its Q3 call in November.

The strong demand reflects Cabometyx as "the best-in-class TKI" in kidney cancer, CEO Mike Morrissey said on the call, adding that the drug "is firmly on its way to becoming a $1 billion global brand." To get there, Cabometyx will need to stand out from several in-class competitors—including Pfizer’s Sutent—and the newly emerging immuno-oncology therapies.

Luckily for Exelixis, Cabometyx has so far held its ground. Citing IMS prescription data, Haley said Cabometyx has managed to grow in both market share and volume, as the entire TKI class’s kidney cancer share remains steady even after Bristol-Myers Squibb’s Opdivo-Yervoy combo nabbed U.S. approval in April.

Moving forward, Exelixis has just started a phase 3 study that examines Cabometyx alone and in combination with Roche’s Tecentriq in previously untreated advanced liver cancer. The Tecentriq-Avastin combo has an FDA breakthrough designation in that setting, and Merck and Eisai’s Lenvima already has an approval.

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