MYOGENIC REGULATORY PROTEIN EXPRESSION IN ADULT SOFT-TISSUE SARCOMAS A SENSITIVE AND SPECIFIC MARKER OI SKELETAL-MUSCLE DIFFERENTIATION

Myogenic regulatory protein (MyoD1) is a DNA-binding nuclear protein t hat initiates myogenesis in mesenchymal stem cells. Its expression has proved a very sensitive marker of myogenic differentiation in maligna nt tumors of childhood In this study, the reliability of MyoD1 express ion as marker of skeletal muscle differentiation has been tested in 38 cases of adult-type sarcomas. Frozen sections were stained with the m onoclonal antibody 5.8A (MAb 5.8A) developed against recombinant wild- type murine MyoD1. Routinely processed formalin-fixed sections from th e same cases were reviewed and immunostained with a panel of antibodie s commonly used to detect muscle differentiation: myoglobin, fast-myos in, desmin, muscle-specific actin, alpha-smooth muscle actin. Four cas es positively stained with MAb 5.8A: three were high-grade spindle cel l sarcomas, the fourth case was an alveolar soft-part sarcoma. Only tu mors in which skeletal muscle histogenesis was inferred on the basis o f histology and/or immunohistochemistry with conventional muscle marke rs stained positively for MAb 5.8A. All the other tumors tested, inclu ding leiomyosarcomas (11), liposarcomas, (10, including four dediffere ntiated liposarcomas), fibrosarcomas (three), malignant fibrous histio cytomas (two), synovial sarcomas (two), and malignant peripheral nerve sheath tumors (two), were negative for MAb 5.8A. The high level of se nsitivity and specificity of MyoD1 expression indicates the value of t his marker in the diagnosis of soft tissue sarcomas.