Birgitta Versluijs

16 1 Pulmonary complications of HCT Reported incidence rate of BOS in literature varies widely from 0-48%, depending on de- finition and cohort of patients. Prognosis is poor, with improvement of lung function on aggressive therapy in only 8-20% and mortality rates of 50-80%. In many reports BOS following HCT is seen as a chronic progressive disease leading to irreversible air flow obstruction, with patients usually dying from pneumonia. 12,18 Cryptogenic Organizing Pneumonia (COP; formerly called Bronchiolitis Obliterans Organizing Pneumonia , BOOP) is also considered a late non-infectious lung complication of HCT, with an incidence of 1-2%. COP usually develops earlier than BOS, has a more acute onset and is accompa- nied by fever. COP has a better prognosis with good response to corticosteroid therapy and mortality rate of around 19%. 12,13 In all abovementioned disease-entities (allo)immunity and pro-inflammatory state play an important role. The clinical observation that there was an increase in the incidence of Allo-immune mediated Lung Syndromes (Allo-LS) in our pediatric HCT patients, with a very poor outcome raised our interest in this subject, and was the basis for this thesis.