Gliosarcoma with alveolar rhabdomyosarcoma-like component: report of a case with a hitherto undescribed sarcomatous component

Gliosarcoma (GS) is a relatively rare glioblastoma variant characterized by biphasic glial and mesenchymal differentiation patterns. The sarcomatous part most commonly resembles fibrosarcoma or so-called malignant fibrous histiocytoma. Rarely, GS shows heterologous lines of differentiation in the form of osteosarcoma, chondrosarcoma, liposarcoma, leiomyosarcoma, squamous or glandular malignant epithelial differentiation, or primitive neuroectodermal tumor (PNET)-like foci. When rhabdomyoblastic differentiation occurs, it is in the form of malignant spindle cells, with cross-striated strap cells or rounded rhabdomyoblasts reminiscent of the embryonal type of rhabdomyosarcoma. We are reporting a case of GS with an alveolar rhabdomyosarcoma-like component. The tumor consisted of poorly differentiated primitive small round cells growing in a solid and alveolar pattern, with minimal cytoplasm, markedly elevated mitotic activity and numerous apoptotic nuclei. Rhabdomyosarcomatous differentiation was confirmed by desmin and myogenin immunopositivity. To the best of our knowledge, this histologic pattern has not been previously reported in GS. Differential diagnostic considerations are discussed. gliosarcoma - alveolar rhabdomyosarcoma - myogenin - desmin.