Pulmonary leiomyosarcoma arising in pulmonary hamartoma: an exceptional occurrence in a rare tumor.

A solitary peripheral lung nodule was found in the left lung of a 52-year-old man. It was located in the lower lobe and measured 18.5 cm of major axis on chest computed tomography. A tru-cut core biopsy was obtained and a proliferation of bland, monomorphic, spindle cells in interlacing fascicles was observed. Accordingly, a surgical resection of the neoplasm was subsequently carried out. Macroscopically, the tumor appeared as a well-circumscribed nodule with a firm and whitish cut surface. Histologically, the neoplasm was predominantly composed of bland and monomorphic spindle cells, with a predominantly fascicular growth pattern, in which many tubular and cleft-like spaces of entrapped normal respiratory epithelium were involved. Myxoid change, stromal hyalinization and scattered bizarre mononucleated and multinucleated cells were also observed. Based on clinico-morphological, immunophenotypical and molecular features, we made a diagnosis of malignant transformation of pulmonary adenoleiomyomatous hamartoma into pulmonary leiomyosarcoma. As far as we know, this is the first described case of this exceptionally rare occurrence in an already rare neoplasm.