Immunohistochemical profile of myogenin and MyoD1 does not support skeletal muscle lineage in alveolar soft part sarcoma - A study of 19 tumors

Background.-The histogenesis of alveolar soft part sarcoma remains elusive. Myogenic origin is favored, although conflicting data on immunohistochemic al demonstration of muscle-associated markers exist. Myogenin and MyoD1, tr anscription factors of the myogenic determination family, have crucial role s in commitment and differentiation of mesenchymal progenitor cells to myog enic lineage and in maintenance of skeletal muscle phenotype. Their immunoh istochemical detection is specific in characterization of rhabdomyosarcoma. Methods.-Antibodies for myogenin, MyoD1, desmin, and muscle-specific actin were employed on a large series of cases (n = 19) of formalin-fixed, paraff in-embedded alveolar soft part sarcoma. Results.-Minimal scattered nuclear staining was seen with myogenin. All cas es had pronounced, nonspecific granular cytoplasmic immunostaining with Myo D1; nuclei were negative. All tumors were negative for desmin and muscle-sp ecific actin. Ultrastructural study in 10 cases failed to reveal features o f skeletal muscle differentiation. Conclusions.-Cytoplasmic staining with MyoD1 in alveolar soft part sarcoma may correspond to cross-reactivity with an undetermined cytoplasmic antigen . The lack of immunostaining with myogenin, MyoD1,desmin, and muscle-specif ic actin provides evidence against a myogenic origin for alveolar soft part sarcoma.