Seagen's potential breast cancer blockbuster Tukysa shows promise in colorectal cancer

Two years after its approval, Seagen’s potential blockbuster Tukysa is off to a promising start as a treatment for breast cancer. Now the Seattle-area biotech is hoping to expand its use to colorectal cancer patients.       

On Monday, the company revealed successful top-line results from the 2 Mountaineer trial investigating the use of Tukysa plus chemotherapy (Roche's Herceptin) on patients with previously treated HER2-positive metastatic colorectal cancer (mCRC).

Of 117 patients to receive the treatment, 38% experienced a complete or partial response, allowing the trial to meet its primary objective. Of those who achieved response to the regimen, their median duration without tumor growth was 12.4 months. The trial didn't have a placebo arm.

Analysts at SVB Securities noted that while the ORR (response rate) fell short of the 52% figure Seagen reported for its trial of Tukysa in 2019, that study included only 23 patients. On the plus side, the duration of response (mDOR) exceeds the previously reported 10.4 months.

“The longer duration of response could be an encouraging indicator of other durability parameters, such as progression-free survival and overall survival (OS), as well as a key lever of the commercial opportunity,” analyst wrote Andrew Berens in a note to clients.

The medicine also was well-tolerated, Seagen said. About 20% or more of patients experienced side effects that included diarrhea, fatigue, nausea or infusion-related reaction.

Seagen plans to submit a new drug application to the FDA under its accelerated approval program.

SVB analysts believe the drug could generate peak sales of $542 million in the tumor type.

Earlier this year, Seagen reported sales of Tukysa at $334 million in its first full year on the market. The drug won its original FDA nod for advanced unresectable or metastatic HER2-positive breast cancer in April 2020 and its peak sales were tagged at $1.6 billion in that indication.

Later this summer, trial investigator John Strickler, M.D., of Duke University Medical Center, will present full data from 2 Mountaineer at the European Society for Medical Oncology World Congress on Gastrointestinal Cancer in Barcelona.