Gossamer Bio reported a pivotal Phase III miss for seralutinib in pulmonary arterial hypertension (PAH), with the study failing to meet its primary endpoint amid an outsized placebo response. The announcement triggered a steep share price collapse and prompted the company to pause enrollment in a second Phase III study while it pursues additional analyses and regulatory dialogue. BioCentury coverage and company statements noted elevated adverse‑event signals including cough and liver enzyme elevations; Gossamer said it will engage the FDA to assess potential paths forward despite the negative topline result.