Diagnosis and behavior of juvenile rhabdomyosarcoma.

The main problems in the diagnosis of rhabdomyosarcoma are 1) distinction of undifferentiated examples from other small cell malignancies, especially soft-tissue Ewing's tumor and lymphoma; 2) distinction of spindling examples from fibrosarcoma, leiomyosarcoma, malignant fibrous histiocytoma, polyhistioma, and other sarcomas; 3) recognition of minimal criteria on small samples such as needle biopsy specimens or frozen sections; and 4) recognition of rhabdomyosarcoma in uncommon sites such as bone (mandible), perineum, retroperitoneum, and chest. In 95 pediatric cases diagnosed and treated at Royal Alexandria Hospital for Children--45 after the introduction of combined therapy--minimal diagnostic criteria were assessed. Cross-striations were found in only one third of cases; longitudinal myofibrils were more common and more helpful. There was much overlap between histologic types, and the microscopic patterns had little bearing on prognoses in preadolescent children. Fourteen cases could not be further differentiated ("embryonal sarcoma, probably rhabdomyosarcoma")--nine small-cell tumors; four tumors from genitourinary tract or head for which very small biopsy specimens were available, and one spindling retroperitoneal neoplasm. In all, slight evidence suggested embryonal rhabdomyosarcoma; this evidence included oat-shaped nuclei and, in a few cells, deeply eosinophilic cytoplasm, small elongated processes, or myxoid or alveolar foci--features that exclude lymphoma and Ewing's tumor. In six cases that were originally classified as poorly differentiated or undifferentiated, later material confirmed the presence of rhabdomyosarcoma by showing a predominantly well-differentiated (pleomorphic) or alveolar pattern after therapy. In 14 remaining undifferentiated cases, immunoperoxidase staining with antihuman-myoglobin serum was positive in five. With combined therapy there was 100 per cent survival among patients with paratesticular, limb, and stage I and stage II tumors; considerably improved survival among patients with head and neck, pelvic, and stage III tumors; and 100 per cent mortality among patients with intra-abdominal and stage IV tumors.