Abstract
Background : Alveolar soft part sarcoma (ASPS) is a rare soft tissue tumor that usually affects the extremities of young patients. Herein, we report a case of metastatic ASPS of the lungs diagnosed prior to the primary tumor in the thigh.
Case : A 35-year-old female who was diagnosed as having multiple tumors in both lungs underwent thoracoscopic partial lung resection. In the imprint cytology specimen, many atypical cells with round nuclei and prominent nucleoli were found dispersed either in loose cohesive clusters or as single cells. The atypical cells had abundant finely granular cytoplasm and intracytoplasmic diastase-resistant, PAS-positive rod-shaped crystals. In addition, the nuclei of the atypical cells showed positive immunoreactivity for TFE3. The cytologic findings were suggestive of ASPS metastasis to the lungs. Histological examination also revealed features consistent with ASPS. On electron microscopy, crystals consisting of filaments arranged in parallel were observed in the cytoplasm. Furthermore, reverse-transcriptase PCT analysis revealed ASPL-TFE3 fusion gene transcripts. Then, a careful search for the primary lesion revealed the primary tumor in the right thigh.
Conclusion : ASPSs are often detected as metastatic foci prior to the diagnosis of the primary lesion. Examination of the cytology material obtained from the metastatic tumor is useful for obtaining the correct diagnosis.
