Creatine kinase subunits M and B as markers in the diagnosis of poorly differentiated rhabdomyosarcomas in children.

Antibodies against the M and B subunits of creatine kinase were assessed for their usefulness in the diagnosis of poorly differentiated rhabdomyosarcoma. Routinely processed formaldehyde-fixed tissue and the avidin-biotin-peroxidase complex technique were used. The majority of the poorly differentiated and all of the moderately and well-differentiated rhabdomyosarcomas studied showed immunostaining for the M subunit. The rhabdomyoblastic component of malignant "triton" tumors was also positive. Staining, although weak compared with that of the rhabdomyosarcomas, was also observed in a few leiomyosarcomas, hemangioendotheliosarcomas, malignant fibrous histiocytomas, and ganglioneuroblastomas. On the other hand, staining for the B subunit was seen in many types of soft tissue tumors, including rhabdomyosarcoma, Ewing's sarcoma, and (ganglio)neuroblastoma. The results indicate that creatine kinase subunit M is a useful marker for distinguishing poorly differentiated rhabdomyosarcoma from other types of small round cell tumors in children, such as neuroblastoma, Ewing's sarcoma, and malignant lymphoma.