Alveolar soft tissue sarcoma

: Clinical and morphological manifestations of alveolar soft tissue sarcoma (ASTS) are presented on the basis of 19 examinations performed by the authors and data available in the literature. ASTS has been found to be more common in young women and to be usually located in the thick layers of the proximal parts of the extremities. The tumor generally shows slow growth and late occurrence of metastases. It has been demonstrated that ASTS has an organoid structure, namely alveolar grouping of cells, abundance of capillaries, and its cells contain PAS-positive inclusions. In atypical ASTS, the prognosis has been found to be less favourable. The crystalloid inclusions that are absent in other soft tissue neoplasms are a characteristic ultrastructural sign of ASTS. The genesis of ASTS remains controversial but it cannot be ruled out that it is related to the elements of the APUD-system.