Crystal-deficient alveolar soft-part sarcoma with cutaneous involvement: a case report.

Alveolar soft-part sarcoma (ASPS) is a rare distinctive sarcoma, in most cases involving deep soft tissues of the extremities. It is associated with a specific unbalanced translocation, der(17)t(X;17)(p11;q25) that results in the formation of an ASPL-TFE3 fusion gene. Microscopically, it is typified by an alveolar growth of large cells containing typical periodic acid-Schiff-positive rod-shaped crystals, often serving as a diagnostic clue. Other distinctive features include nuclear immunoreactivity for transcription factor 3 (TFE3) protein and a typical ultrastructural finding of large crystals with a rectangular or rhomboid shape. The authors present an unusual case of ASPS with cutaneous involvement, which did not exhibit typical large crystals; there were striking round granules. Molecular genetic study revealed fusion transcript ASPL-TFE3, type 2. To the best of our knowledge, cutaneous involvement of a crystal-deficient ASPS has not been reported.