Cellular differentiation and prognosis in embryonal rhabdomyosarcoma. A report from the Cooperative Soft Tissue Sarcoma Study 1981 (CWS 81).

Sixty-four cases of embryonal rhabdomyosarcoma (eRMS) were investigated for cellular differentiation by light microscopy. Of these 64 cases 20 were studied by means of immunohistochemistry. Histologically, three subgroups could be distinguished: primitive (less than 10% rhabdomyoblasts), intermediate (10-50% rhabdomyoblasts) and well differentiated (greater than 50% rhabdomyoblasts) eRMS. Vimentin-positive cells predominated in the primitive eRMS. Intermediate eRMS showed large proportions of desmin-positive cells but vimentin containing cells were also numerous. Myoglobin could only be demonstrated in well differentiated eRMS. Primitive and well differentiated eRMS mainly occurred in the head and neck area, whereas intermediate eRMS were predominantly located in the abdomen. Stage III and IV tumours predominated in cases of primitive eRMS, whereas lower stages were noted in cases of intermediate and well differentiated eRMS. Response to chemotherapy, evaluated after seven weeks of treatment, was achieved in 10/15 (66%) cases of primitive, in 16/19 (84%) cases of intermediate and 5/5 cases of well differentiated eRMS. It is concluded from the current study that the three subgroups of eRMS differ not only by cytological differentiation but also by site of predilection, stage at time of diagnosis and response to chemotherapy.