Metastatic alveolar soft part sarcoma of the lung: Metastatic alveolar soft part sarcoma of the lung‐a morphologic pitfall on cytology and aberrant CD10 expression on histology

Abstract

Alveolar soft part sarcoma (ASPS) is a rare aggressive soft tissue sarcoma of young adults, typically arising in the deep soft tissue of lower extremities. Although cytomorphology is characteristic enough for an accurate diagnosis in typical clinical scenarios, problems arise when it occurs in older patients, atypical sites, or in primary evaluation at metastatic sites. A 48-year-old smoker presented with breathlessness and headache for 2 months. Imaging showed a heterogeneous enhancing lesion of 6 cm × 6 cm in right middle lobe of lung, smaller miliary nodules in bilateral lungs, multiple bilateral cerebral lesions, and a mass of 3 cm × 3 cm in the left thigh. Primary lung carcinoma with brain and thigh metastases was the clinical diagnosis. Fine-needle aspiration smears of the lung lesion showed cohesive fragments of large cells with a prominent traversing branching capillary network and discohesion at periphery resulting in a pseudo-papillary appearance. Tumor cells had fine granular to vacuolated cytoplasm, frayed borders, and prominent nucleoli. Trucut biopsy from the same showed a tumor arranged in nests composed of large polygonal cells, immunopositive for CD10. Possibility of metastatic renal cell carcinoma (RCC) was offered. Abdominal imaging was, however, normal. Core biopsy from thigh showed a similar tumor, immunonegative for epithelial markers, with cytoplasmic periodic-acid-schiff positive rhomboid crystals, clinching the final diagnosis of ASPS with lung and brain metastases. There is considerable morphological and immunohistochemical overlap between ASPS and RCC. Bare nuclei on air dried smears, binucleation, metachromatic basement membrane material are subtle pointers toward ASPS. Diagn. Cytopathol. 2015.