Keros Therapeutics Discontinues Cibotercept for PAH, Announces Strategic Restructuring

Keros Therapeutics, a prominent biotech company, has announced the discontinuation of its fusion protein cibotercept for the treatment of pulmonary arterial hypertension (PAH). This decision comes in the wake of safety concerns and disappointing efficacy results, prompting a significant restructuring of the company's operations.

Safety Concerns and Clinical Setbacks

The development of cibotercept hit a major roadblock in December 2024 when the company detected "unanticipated" cases of pericardial effusion—an abnormal accumulation of fluid around the heart—in patients treated with the drug. This safety signal caused Keros's stock to plummet by more than 70% and led to the suspension of dosing in two higher-dose treatment arms of the ongoing study.

Despite continuing treatment in the lower 1.5-mg/kg arm, Keros encountered additional cases of pericardial effusion in January 2025, including in the remaining dose group. This development forced the company to completely halt dosing in the trial.

Efficacy Results and Competitive Landscape

Recent analysis revealed that cibotercept failed to elicit clinically meaningful improvements in key efficacy measures, including pulmonary vascular resistance and six-minute walk distance. While the data interpretation was complicated by the trial's premature termination, William Blair analysts noted that "it does not appear that cibotercept would be competitive with sotatercept [Merck's Winrevair] on the preliminary evidence."

The trial also reported mortality data, with two cibotercept-treated patients dying due to worsening PAH and one death in the placebo group linked to worsening right heart failure. All mortalities were deemed unrelated to cibotercept.

Strategic Restructuring and Financial Outlook

As a result of cibotercept's discontinuation, Keros has announced a 45% reduction in its workforce, which will be implemented after the legally required 60-day notice period. This move is expected to generate annualized savings of approximately $17 million.

The company is currently undergoing a comprehensive strategic assessment of its business. In April, Keros launched a formal review of potential business alternatives, including a potential sale of the company, business combinations, continued investment in its pipeline, and other transactions. An independent panel of directors has been engaged to oversee this review process.

As of March 31, Keros reported $720.5 million in cash and cash equivalents, which the company believes will sustain its operations into 2029. A preliminary update on the strategic review is expected no later than June 9.