"Atypical steroid response" in a pulmonary inflammatory myofibroblastic tumor

A 6-year-old girl was evaluated for the presence of a paratracheal mass with right upper lobe atelectasis due to an endobronchial mass. Bronchoscopic biopsy established a diagnosis of inflammatory myofibroblastic tumor (IMT) and prednisone initially led to a significant reduction of the endobronchial lesion. However, 8 weeks later, when still on prednisone, the mediastinal mass enlarged dramatically. At thoracotomy, a well-circumscribed, multilobulated mass was partially resected and a diagnosis of IMT confirmed. Immunosuppression by corticosteroids may have favored the rapid progression of this apparently benign, indolent tumor.