Therapeutic cytodifferentiation in alveolar rhabdomyosarcoma without genetic change of the PAX3-FKHR chimeric fusion gene: a case study.

Alveolar rhabdomyosarcoma (ARMS) is a subtype of rhabdomyosarcoma and usually occurs in childhood and adolescence. ARMS is characterized by its aggressive behavior and poor prognosis. To improve the unfavorable prognosis, new therapeutic developments and the establishment of methods for precise prognostic prediction are required. We describe a case of ARMS, solid variant, which occurred in a 10-year-old boy. After chemotherapy and radiotherapy, the tumor morphologically and immunohistochemically showed marked cytodifferentiation, whereas the exact same PAX3-FKHR chimeric fusion gene transcript was detected in samples before and after treatment. The result of this study seems to indicate that therapeutic cytodifferentiation does not always correlate with genetic change and favorable prognosis in ARMS.