Metastatic behavior of rhabdomyosarcoma

Embryonal and alveolar rhabdomyosarcoma probably have the same histogenesis, yet alveolar rhabdomyosarcoma has a considerably worse prognosis and is generally less responsive to treatment. The metastatic behavior of rhabdomyosarcoma in 22 autopsied subjects was analyzed with respect to the histologic subtypes of the tumors to determine whether the more aggressive behavior of alveolar rhabdomyosarcoma was related to greater tumor burden and/or more widely disseminated metastases. Subjects with embryonal rhabdomyosarcoma tended to survive longer and had greater numbers of metastatic sites at autopsy compared to subjects with alveolar rhabdomyosarcoma, but these differences were not statistically significant. In addition, there were no significant differences in the overall distribution of metastases between embryonal and alveolar rhabdomyosarcoma. The most frequent sites of metastases from both types of tumor were soft tissues (73%), serosal surfaces (64%), lymph nodes (64%), lungs (55%), and bone marrow (50%). The findings suggest that the metastatic behavior of rhabdomyosarcoma does not vary as a function of length of survival, mode of therapy, or histologic subtype. We propose that factors such as stage of disease at presentation and location of the primary tumor, rather than histologic subtype, are probably the most important variables governing the therapeutic responsiveness of rhabdomyosarcoma.