Is fetal cellular rhabdomyoma an entity or a differentiated rhabdomyosarcoma? A study of patients with rhabdomyoma of the tongue and sarcoma of the tongue enrolled in the intergroup rhabdomyosarcoma studies I, II, and III.

A tumor of the tongue with features consistent with the diagnosis of fetal cellular rhabdomyoma was seen in an 18-month-old infant. The tumor recurred 10 and 22 months after initial resection. The histologic condition of the first recurrence was similar to the original tumor except for some increased nuclear irregularities and mitotic activity. No adjunctive therapy was administered initially or after the first recurrence. The second recurrence showed mixed embryonal/alveolar rhabdomyosarcoma. This case represented a unique model of a highly differentiated striated muscle tumor converting to a moderately differentiated rhabdomyosarcoma, and illustrated differential diagnostic difficulties in distinguishing between fetal cellular rhabdomyoma and differentiated rhabdomyosarcoma. The patient was compared with eight children and adolescents with primary sarcomas of the tongue who entered the Intergroup Rhabdomyosarcoma Studies (IRS) I, II, and III protocols. The tumors of all eight arose at the base of the tongue. There were five embryonal, one alveolar, and one mixed embryonal/alveolar rhabdomyosarcomas, and one undifferentiated myxoid sarcoma. Five rhabdomyosarcomas were poorly differentiated, and two had a moderate degree of myogenesis. These sarcomas of the tongue represent approximately 0.34% of all cases entered in IRS studies.