Bronchiolitis obliterans syndrome (BOS) is a significant complication after allogeneic hematopoietic stem cell transplantation (HSCT). However, the pathogenesis and risks for the development of BOS have remained unclear. Therefore, a case-control study was conducted to investigate the risk factors for the development of BOS, which included the largest number of BOS cases; 196 patients with BOS were identified and compared with 1960 control recipients. The following were identified as significantly higher risk factors for the development of BOS: female recipients (OR 1.47, P = 0.019), ABO-mismatch HSCT (minor mismatch, OR 1.67, P = 0.015; major mismatch, OR 1.73, P = 0.012; bidirectional mismatch, OR 1.96, P = 0.018), busulfan+cyclophosphamide-based myeloablative conditioning (OR 1.74, P = 0.016), and acute graft-versus-host disease (GVHD) involving the skin (OR 1.55, P = 0.011). On the other hand, the risk for the development of BOS was significantly lower in patients receiving cord blood transplantation (OR 0.26, P = 0.0011). With respect to other target organs of chronic GVHD, ocular involvement was significantly associated with BOS (OR 2.53, P < 0.001). Prospective studies are required to elucidate the risk factors for the development of BOS, and future investigations should focus on finding a prophylactic approach against BOS based on these findings.
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