Although encouraging survival statistics are now reported after hematopoietic stem cell transplantation (HSCT), pulmonary complications occur in up-to half of patients after HSCT and are major causes of morbidity and mortality. In this study, we describe cryptogenic organizing pneumonia (COP) after allogeneic HSCT in our institution between January 1986 and December 2005. Charts and chest radiographs of 601 transplant recipients were retrospectively reviewed for COP. Total 12 cases of COP were observed (2.0%) at a median interval of 148 days after HSCT (range, 53–475 days). They presented low-grade fever, non-productive cough and dyspnea at the onset of COP. The initial antibiotics treatment did not ameliorate these symptoms, but all patients well responded to 0.5–1mg/kg of prednisolone. However, in 9 out of 12 patients, COP eventually flared-up after the tapering-off of steroid, but responded to the retreatment. Although 3 patients died, there was no death due to pulmonary failure and 5-year survival was 74.1%. In remaining 9 patients, there was no relapse of primary disease for which the patient underwent HSCT. The clinical features of 12 patients were similar in that they all received an irradiation containing conditioning and most patients had a history of acute graft-versus-host disease (GVHD). Furthermore, 8 patients had active chronic GVHD (6 extensive and 2 limited) at the onset of COP. These findings suggest that both the irradiation and allogeneic immune reaction may play a crucial role in the development of COP after HSCT. Moreover, the patients with COP might enjoy a relatively good prognosis due to low rate of relapse of primary disease through graft-versus-leukemia reaction, even though facing multiple episodes of disease exacerbation of COP.

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