Is anti-h-caldesmon useful for distinguishing smooth muscle and myofibroblastic tumors? An immunohistochemical study

Misinterpretation of positive staining of antibodies to desmin, smooth musc le actin, and muscle actin as representing smooth muscle differentiation in the context of a spindle cell tumor is not uncommon. Anti-h-caldesmon is a promising novel immunohistochemical reagent for more specific smooth muscl e differentiation. We studied 72 tumors (II leiomyosarcomas, 26 malignant f ibrous histiocytomas [MFHs], 11 fibromatoses, 11 cellular cutaneous fibrous histiocytomas [CCFHs], 5 malignant peripheral nerve sheath tumors, 4 synov ial sarcomas, and 4 cases of nodular fasciitis), the reactive myofibroblast ic response in 5 cases of acute cholecystitis, and the desmoplastic respons e surrounding 5 invasive breast carcinomas. Tissues were examined for expre ssion of h-caldesmon, desmin, smooth muscle actin, and muscle actin. Diffus e staining for h-caldesmon was present only within the leiomyosarcomas. Foc al staining for h-caldesmon involving less than 1% of lesional cells was pr esent in 3 of 26 MFHs and 1 of 1 CCFHs. There was overlap in staining for t he other "myoid" markers in all of the lesions that contained myofibroblast s. Anti-h-caldesmon seems to be a reliable marker of smooth muscle differen tiation, and its inclusion in a panel of myoid immunohistochemical reagents should allow distinction of smooth muscle and myofibroblastic tumors.