Pathology of Alveolar Soft Part Sarcoma

Abstract

Alveolar soft part sarcoma (ASPS) is a rare orphan sarcoma of uncertain differentiation according to the latest WHO classifcation of soft tissue tumors with a somewhat indolent clinical course. The common histomorphological alveolar-type presentation is unique. It is usually not graded according to the French Federation of Cancer Centers grading system, but nonetheless defined as a high-grade sarcoma. The tumor adopts a clinical pattern with a distinctive natural history marked by local recurrences up to 50% of cases and a high prevalence of metastases in such diverse sites such as the lung, liver, brain, bone that can occur more than 10 years after the primary event. ASPS is driven by a specific recurrent nonreciprocal translocation der(17)t(X;17)(p11;q25). This chimeric gene fusion is also found (albeit in the balanced mode) in a subset of renal cell carcinomas in the young. Nevertheless, its high specificity and sensitivity in ASPS is a recognized feature and accurate diagnosis requires trained pathologists and molecular testing. Prognostication is based on age, size of tumor, primary site, and the presence or not of metastasis.