Expression of myogenic marker proteins in human leiomyosarcoma

A series of formalin-fixed, paraffin-embedded leiomyosarcomas (n = 11) was studied immunohistochemically for their expression of various myogenic marker proteins. According to their predominant histological appearance, the tumors were classified as well (n = 4), moderately (n = 5), or poorly (n = 2) differentiated. Using monoclonal anti-muscle specific actin antibodies from clone HHF35 all examined tumors were positively stained. Desmin was not always found in leiomyosarcomas, since positive staining could be demonstrated only in eight cases. As revealed by staining with anti-vinculin antibodies from clone hVIN-1 using the APAAP technique, all leiomyosarcomas with the exception of one expressed vinculin. Typically, the vinculin immunoreactivity was detected diffusely throughout the majority of neoplastic cells as well as in vascular smooth muscle cells of blood vessels. Nine leiomyosarcomas displayed a positive staining for calponin, an actin-binding protein expressed in smooth muscle cells and their precursors. The distribution of calponin resembled that of vinculin in decorating myofibrils of nearly all tumor cells. Actinin immunoreactivity was present in tumor cells of all cases, but was expressed also in nontumor cells such as epithelia. These results suggest that the monoclonal antibodies against vinculin and calponin may serve as additional diagnostic markers for myogenic differentiation in leiomyosarcomas and related tumors.