Insmed (INSM) said Thursday that 12-month data from an ongoing open-label extension study showed its investigational treprostinil palmitil inhalation powder provided sustained improvement across all efficacy endpoints in patients with pulmonary arterial hypertension.

The company said patients continuing the treatment and those who switched from placebo showed similar benefits at 12 months, including mean improvement of over 55 meters in six-minute walk distance, roughly 60% reduction in NT-proBNP levels, and improved World Health Organization functional class.

Insmed said the findings support the ongoing phase 3 trial evaluating its drug over 24 weeks.

Shares of Insmed were down more than 1% pre-bell Thursday.