Alveolar rhabdomyosarcoma with neuroendocrine/neuronal differentiation: report of 3 cases.

The aim of this study is to report the clinicopathologic characteristics of 3 cases of alveolar rhabdomyosarcoma with neuroendocrine/neuronal differentiation. Specimens of 3 cases of alveolar rhabdomyosarcoma were studied using histologic, immunohistochemical, ultrastructural, and molecular genetic techniques. The patients were a 19-year-old man with metastatic alveolar rhabdomyosarcoma in a groin lymph node, a 16-year-old girl with alveolar rhabdomyosarcoma of the perineum, and a 20-year-old man with recurrent orbital alveolar rhabdomyosarcoma. Microscopically, case 1 was composed of compact sheets of medium to large tumor cells. Cases 2 and 3 were small blue round cell tumors. Cases 1 and 3 were solid throughout, whereas case 2 demonstrated alveolar and solid architecture. By immunohistochemistry, the following markers were positive: desmin (3/3), myogenin (3/3), synaptophysin (3/3), and chromogranin (2/3). Ultrastructurally, sarcomeric filaments were seen in all cases, while neuroendocrine granules were detected only in case 1. PAX:FKHR fusion transcript was identified in case 2, case 3 had a variant PAX3 transcript, and case 1 was negative. The data presented expands the known differentiation of alveolar rhabdomyosarcoma.