Clinical response to belumosudil in bronchiolitis obliterans syndrome: a combined analysis from 2 prospective trials

Chronic graft-versus-host disease (cGVHD) of the lung, or bronchiolitis obliterans syndrome (BOS), is a high-risk disease manifestation associated with poor outcomes. Currently available treatments have demonstrated limited clinical efficacy in this setting. Belumosudil is a novel oral selective rho-associated coiled-coil–containing protein kinase-2 inhibitor that was recently approved by the US Food and Drug Administration in the treatment of cGVHD. We identified 59 subjects with BOS who were enrolled and treated in 2 prospective clinical trials of belumosudil. Patients with BOS had a percentage predicted forced expiratory volume in 1 second (FEV1) of ≤79% at enrollment and clinician attribution of lung disease owing to cGVHD. The National Institutes of Health (NIH) cGVHD lung scores at enrollment were 1 (n = 30, 59%), 2 (n = 23, 39%), or 3 (n = 6, 10%). According to NIH response criteria, the best overall response rate (ORR) for lung cGVHD was 32% (partial response: 17%; complete response: 15%). Response rates were inversely proportional to baseline NIH GVHD lung score at enrollment (lung score 1: ORR 50%; lung score 2: ORR 17%, lung score 3: ORR 0%) (P = .006). In multivariable analysis, male sex, lower baseline NIH cGVHD lung score, and partial response to previous line of cGVHD therapy before enrollment were associated with higher rates of lung-specific response. No significant correlation was identified between pulmonary function evaluations and measures of patient symptoms (NIH lung symptom score or Lee Symptom Scale score for lung). In conclusion, belumosudil treatment was associated with lung-specific clinical responses for subjects with BOS, which were more commonly observed in less advanced disease. Optimization of treatment response evaluations remains a challenge in patients with BOS.