BackgroundHereditary hemorrhagic telangiectasia (HHT) is characterized by extensive telangiectasias and arteriovenous malformations. The primary clinical manifestation is epistaxis that results in iron-deficiency anemia and reduced health-related quality of life.MethodsWe conducted a randomized, placebo-controlled trial to evaluate the safety and efficacy of pomalidomide for the treatment of HHT. We randomly assigned patients, in a 2:1 ratio, to receive pomalidomide at a dose of 4 mg daily or matching placebo for 24 weeks. The primary outcome was the change from baseline through week 24 in the Epistaxis Severity Score (a validated bleeding score in HHT; range, 0 to 10, with higher scores indicating worse bleeding). A reduction of 0.71 points or more is considered clinically significant. A key secondary outcome was the HHT-specific quality-of-life score (range, 0 to 16, with higher scores indicating more limitations).ResultsThe trial was closed to enrollment in June 2023 after a planned interim analysis met a prespecified threshold for efficacy. A total of 144 patients underwent randomization; 95 patients were assigned to receive pomalidomide and 49 to receive placebo. The baseline mean (±SD) Epistaxis Severity Score was 5.0±1.5, a finding consistent with moderate-to-severe epistaxis. At 24 weeks, the mean difference between the pomalidomide group and the placebo group in the change from baseline in the Epistaxis Severity Score was −0.94 points (95% confidence interval [CI], −1.57 to −0.31; P=0.004). The mean difference in the changes in the HHT-specific quality-of-life score between the groups was −1.4 points (95% CI, −2.6 to −0.3). Adverse events that were more common in the pomalidomide group than in the placebo group included neutropenia, constipation, and rash.ConclusionsAmong patients with HHT, pomalidomide treatment resulted in a significant, clinically relevant reduction in epistaxis severity. No unexpected safety signals were identified. (Funded by the National Heart, Lung, and Blood Institute; PATH-HHT Clinicaltrials.gov number, NCT03910244).