Fetal heavy chain skeletal myosin. An oncofetal antigen expressed by rhabdomyosarcoma.

Fetal heavy chain skeletal myosin is normally present in fetal skeletal muscle. The study of 21 cases of rhabdomyosarcoma using specific antisera for fetal myosin, as well as for slow myosin, myoglobin, and desmin, led to positive findings in all cases with at least one antiserum. Desmin was localized in all cases and fetal myosin in 17 cases (81%), while myoglobin and slow myosin were present in 11 and eight cases, respectively. The localization of fetal myosin in rhabdomyosarcoma indicates that it is a type of oncofetal antigen. Because fetal myosin is found in small rhabdomyoblasts, it can be a useful marker in cases that usually constitute diagnostic problems.