Immunohistochemistry of myoglobin in rhabdomyosarcomas.

Immunoperoxidase staining for myoglobin was performed on formalin-fixed, paraffin-embedded tissues of normal human skeletal muscle and rhabdomyosarcomas in order to assess its potential diagnostic value. Myoglobin-positive cells were observed in normal adult and fetal muscles, and in 13 of 26 rhabdomyosarcomas. In normal skeletal muscle, the intensity of staining for myoglobin varied in individual cells. Of the 13 myoglobin-positive rhabdomyosarcomas tested, 6 showed cross striations in tumor cells, whereas the others did not. Myoglobin-positive tumor cells were not demonstrated in two rhabdomyosarcomas in which cross striations were observed. In other types of tumors examined that sometimes resembled rhabdomyosarcomas, no myoglobin was detected. Thus tests for myoglobin by the immunoperoxidase method seem helpful in identifying rhabdomyosarcomas and confirming their histological diagnosis.