Alveolar soft part sarcoma of the pulmonary vein

Alveolar soft part sarcoma of the lung seen in a 42-year-old female is reported. In the partial pneumonectomy specimen, there was a 3 x 2.5 cm tumor arising from the pulmonary vein at the level of the right lung hilus, with tumor thrombus formation. The transition between the tumor and venous smooth muscle layer was microscopically confirmed. At autopsy, performed 18 months after surgery, metastases were noted in the left lung and brain. No primary focus was identified in the soft tissue. The alveolus-forming clear tumor cells contained diastase-resistant periodic acid-Schiff-reactive granules. Immunohistochemically, granular cytoplasmic reactivities with monoclonal antibodies against pan-actin and alpha-sarcomeric actin were demonstrated, whereas other muscle markers such as desmin, alpha-smooth muscle actin, myoglobin, fast skeletal myosin, and the mm-isozyme of creatine kinase were negative. Ultrastructurally, crystallized structures were occasionally identified in the membrane-bound, electron lucent granules, which often filled the tumor cell cytoplasm. The muscle cell nature of the neoplasm is discussed.