Gossamer ends $486M PAH partnership with Chiesi after phase 3 miss

Gossamer Bio announced it is terminating its collaboration and licensing agreement with Italy's Chiesi, regaining worldwide development and commercial rights to its pulmonary arterial hypertension candidate seralutinib.

The decision follows a phase 3 trial in which seralutinib showed a placebo‑adjusted improvement of 13.3 meters in six‑minute walk distance, but the result did not meet the prespecified statistical threshold of 0.025 (p=0.032). While four secondary measures favored the drug, the primary endpoint shortfall prompted the split.

Under the original deal, Chiesi had paid $160 million as a development reimbursement and the agreement included potential regulatory milestones of up to $146 million and sales milestones of up to $180 million. Pulmonary arterial hypertension affects roughly 40,000 people in the United States, a rare and rapidly progressing condition.