Immunoperoxidase demonstration of a new muscle protein (Z-protein) in myogenic tumors as a diagnostic aid.

Z-protein, a new muscle protein with a molecular weight of 55,000 daltons recently discovered in Japan, is an excellent marker for muscle differentiation in paraffin sections. Positive staining by a peroxidase-antiperoxidase technique for detection of intracellular Z-protein was observed in 2 of 2 cardiac rhabdomyomas, 5 of 5 leiomyomas, 9 of 10 leiomyosarcomas, and in 15 of 18 rhabdomyosarcomas including 5 of 5 of the pleomorphic type, 7 of 9 of the embryonal type, and 3 of 4 of the alveolar type. Other types of tumors (77 cases) that sometimes mimic myogenic tumors on histologic examination gave negative results. The immunoperoxidase method for detection of intracellular Z-protein is of use in distinguishing myogenic tumors from other types of tumors.