Preemptive Intervention in Airflow Obstruction Status Prevents the Development of Bronchiolitis Obliterans Syndrome after Allogeneic Stem Cell Transplantation: Multicenter, Prospective Phase II Study (Chiba AFO-01)

Background: Bronchiolitis obliterans syndrome (BOS) after allogeneic hematopoietic stem cell transplantation (allo-HCT) is recognized as pulmonary chronic graft-versus-host disease (GVHD), a progressive, irreversible, and sometimes fatal complication. Periodic pulmonary function testing (PFT) for early diagnosis and timely therapeutic intervention is essential. However, effective monitoring and adequate treatment strategy for BOS have not been established. The airflow obstruction (AFO) criteria (predicted FEV1 second decreased by 5% a year or more, and FEV1-second rate