Histopathological classification of childhood rhabdomyosarcomas: relationship with clinical parameters and prognosis

To define a useful and prognostically relevant classification system for rhabdomyosarcomas (RMSs), tissue sections of 113 well-documented, protocol-treated cases were retrieved from the files of the Emma Kinderziekenhuis Amsterdam, the Netherlands, and reclassified by a panel of pediatric pathologists. The following subtypes were recognized: embryonal RMS (n = 66), alveolar RMS (including the solid variant) (n = 16), botryoid RMS (n = 11), embryonal sarcoma (n = 6), and spindle cell RMS (n = 5). Nine cases were classified as RMS not otherwise specified (NOS). The above-mentioned histopathological subtypes correlated significantly with survival (P = .005) in patients with nonparameningeal tumors. Indeed, the best prognosis was observed in patients with spindle cell RMS, embryonal sarcoma, and botryoid RMS (10-year survival rates of 80% to 86%). Patients with embryonal RMS had an intermediate prognosis (10-year survival rate of 55%) and patients with alveolar RMS fared poorly (10-year survival rate of 9%). Survival rate was poor in patients with a localized parameningeal tumor, irrespective of histopathological subtype (10-year survival rate of 33%). Furthermore, this study confirmed the known impact on prognosis of localization (P = .008) and tumor node metastasis (TNM) stage (P = .0005). Classification of RMS subtypes proved to be fairly well reproducible (kappa ranging from 0.47 to 0.85 and percentage of concordance ranging from 50% to 85%). The best agreement was noted in botryoid RMS and the worst in embryonal sarcoma. However, improvement of agreement was noted for the latter subtype during the consecutive classification sessions. In summary, this study shows the strong prognostic value of histopathological subtypes and parameningeal tumor localization.