Primary primitive peripheral neuroectodermal tumor of the prostate. Immunophenotypic and molecular study of a case.

A case of primitive peripheral neuroectodermal tumor arising in the prostate gland of a 31-year-old man and first diagnosed through a biopsy is reported. Microscopically, the tumor was made up of solid nests and sheets of small round cells, and it was difficult to distinguish the neoplasm from other small round cell tumors, such as small cell carcinoma, rhabdomyosarcoma, or malignant lymphoma. Immunohistochemically, the tumor cells showed immunoreactivity for CD99, vimentin, neuron-specific enolase, and synaptophysin. The neoplasm was excised by a radical surgical procedure preceded by chemotherapy and radiation therapy. The morphologic diagnosis of the prostatectomy specimen was complemented by molecular analysis performed on viable microdissected tissue obtained from formalin-fixed, paraffin-embedded tumor sections. Polymerase chain reaction and sequencing assessment showed the presence of EWS/FLI1 type 2 chimeric transcript, confirming the diagnosis of peripheral primitive neuroectodermal tumor. To our knowledge, this is the first description of a primary peripheral primitive neuroectodermal tumor in the prostate gland.