Myoglobin, an intracellular hemoprotein expressed in the heart and oxidative skeletal myofibres of vertebrates, binds molecular oxygen and may facilitate oxygen transport from erythrocytes to mitochondria, thereby maintaining cellular respiration during periods of high physiological demand. 

Myoglobin is a globular protein which functions as the primary oxygen carrier of muscle tissues. It is found solely in skeletal and cardiac muscle, and therefore it may be used to differentiate rhabdomyosarcoma from other soft tissue tumors.

Anti-myoglobin labels skeletal and cardiac muscle cells. In combination with other striated muscle markers such as vimentin and myogenin, myoglobin is helpful in the identification of rhabdomyosarcoma and tumors with skeletal muscle differentiation. Anti-Myoglobin is also utilized to establish rhabdomyoblastic differentiation in other tumors, such as neurogenic sarcomas and malignant mixed mesodermal tumors of the uterus and ovary. Recently, myoglobin has been reported to be expressed on epithelial cancer cells due to changed metabolic and environmental conditions. Myoglobin expression on cancer cells may play a causative role in tumor progression.