Management Challenges and Outcomes of Bronchiolitis Obliterans Syndrome After Hematopoietic Stem Cell Transplantation: First Case Series Report From Vietnam.

Bronchiolitis obliterans syndrome (BOS) is a serious pulmonary manifestation of chronic graft-versus-host disease (cGvHD) after allogeneic hematopoietic stem cell transplantation (HSCT). Data from low- and middle-income countries remain scarce. We conducted a case series of 11 patients diagnosed with BOS between November 2023 and June 2025 at the National Lung Hospital, Hanoi, Vietnam. Clinical characteristics, treatments, pulmonary function, and outcomes over 12 months were analyzed. The series was predominantly male (81.8%), with a median age of 34 years (range, 12-57). The median time from HSCT to BOS diagnosis was 24 months (range, 11-72). All patients received fluticasone, azithromycin, montelukast (FAM) plus long-acting bronchodilators, and 4 patients also received systemic corticosteroids. Median baseline forced expiratory volume in one second (FEV1) was 1.35 L (range, 0.53-2.48), corresponding to 40% predicted (range, 18-68). Over 12 months, 9/11 patients (81.8%) were hospitalized for respiratory infections, with invasive aspergillosis in 7/14 episodes (50%). Four patients (36.4%) died, three from infections, and one from autoimmune cerebritis. Median survival among deceased patients was 6.5 months. Among survivors, lung function was generally stable, with no significant change in FEV1 across baseline, 3, 6, and 12 months (Friedman test, p value = 0.37). BOS after HSCT in Vietnam was associated with high early mortality and a high incidence of invasive fungal disease. Systemic corticosteroid use appeared to increase infection-related deaths, while steroid-sparing regimens such as FAM combined with bronchodilators stabilized lung function in most survivors. Early detection, antifungal prophylaxis, and steroid-sparing strategies are crucial in this high-risk population.