Alveolar soft-part sarcoma: a new type of rhabdomyosarcoma?

Alveolar soft part sarcoma (ASPS) was described as a distinct entity in 1952. ASPS mainly affects young adults, with a slight prevalence of female patients. It arises in the extremities, trunk, and head and neck region. Metastases are frequent and are mainly localized to lungs, brain, and bone. Local recurrences are rare if the primary tumor is completely excised. Adjuvant chemotherapy or radiotherapy are not useful. Death eventually supervenes, after several years, in most of the patients. Histogenesis and differentiation of ASPS, since its first description, have remained a matter of controversy. Many hypotheses have been taken into consideration, among which neural and muscular differentiation are the most plausible. The finding that intracytoplasmic crystals, present in most of the cases, are composed of actin, and the immunocytochemical localization in ASPS of several muscular markers, such as actin (skeletal and smooth muscle actin), desmin, and MyoD1 are all features that point towards skeletal muscle differentiation.