Seagen touts new Tukysa colorectal cancer data, setting up FDA filing and a potential $500M opportunity

Seagen unveiled full results from a pivotal trial that could expand Tukysa’s use into treatment for colorectal cancer. The new tumor progression and patient survival data make the Seagen med look stronger than Novartis' Tykerb.

A combination of Tukysa and Roche's Herceptin helped patients with previously treated HER2-positive metastatic colorectal cancer live a median 24.1 months. The patients also went median 8.2 months without tumor progression. 

Investigators presented the latest progression-free survival and overall survival data from the phase 2 MOUNTAINEER trial at the European Society for Medical Oncology (ESMO) World Congress on Gastrointestinal Cancer. They add onto the 38% tumor shrinkage rate Seagen unveiled in May.

Seagen plans to use the data to pursue an accelerated approval for Tukysa in patients with previously treated HER2-positive colorectal cancer. Analysts at SVB Securities projected a potential U.S. launch in 2023.

The SVB team noted the latest Tukysa data appeared stronger than those from Novartis' fellow anti-HER2 small molecule, Tykerb, in HER2-positive colorectal cancer. 

In a separate phase 2 trial dubbed HERACLES, a combination of Tykerb and Herceptin triggered a response in 30% of patients. The median time before disease progression or death was 4.8 months for that combo, and patients lived a median of just 10.6 months on that combo.

Tykerb is not approved in colorectal cancer. In fact, there are currently no FDA-approved therapies that specifically target HER2 in colorectal cancer, Seagen noted.

If Tukysa eventually wins a label expansion under the accelerated approval pathway, it'd need to further validate its strength in a confirmatory trial. The Phase 3 MOUNTAINEER-03 study pitting a cocktail of Tukysa, Herceptin and the chemo regimen mFOLFOX6 against standard of care in newly diagnosed HER2-positive metastatic colorectal is already underway, and the SVB team expects a readout in 2024.

All told, the SVB analysts estimated metastatic colorectal cancer could mean $542 million in global peak sales for Tukysa, they said in a Tuesday note.

Tukysa is approved in 36 countries and won its FDA nod back in April 2020. That approval came four months ahead of schedule and marked the company’s first foray into the breast cancer field. Competition to the drug includes Roche’s Kadcyla and AstraZeneca and Daiichi Sankyos Enhertu.