Comparative immunohistochemical staining for desmin and muscle-specific actin: A study of 576 cases

Muscle-specific actin (MSA) and desmin are considered to be sensitive and specific markers for muscle differentiation. The authors compared staining patterns for these markers in 576 samples of normal, reactive, and neoplastic tissues. The standard avidin-biotin-peroxidase complex technique was performed with the use of two commercial antibodies against MSA (HHF35; Enzo Biochemical, Inc., New York, NY) and desmin (DER11; DAKO Corporation, Santa Barbara, CA), respectively, on consecutive paraffin-embedded tissue sections from these cases. Both MSA and desmin were found in all 80 normal muscle samples. Although MSA appeared diffusely in all vascular smooth muscle samples, desmin was demonstrated focally in vascular smooth muscle cells in 100 of 196 samples. MSA but not desmin always was found in myoepithelial cells (25 samples), pericytes (286 samples), and decidual cells (7 samples). Among 76 cases of myofibroblast-containing lesions, 14 and 54 were found to have desmin and MSA, respectively. MSA and desmin were found in 4 of 4 cardiac rhabdomyomas, 34 of 34 rhabdomyosarcomas, and 5 of 6 leiomyomas. Among 22 leiomyosarcomas, 7 displayed either MSA or desmin and 7 showed both markers. In general, more tumor cells showed staining for MSA than desmin, but the reverse was true in some cases. Tissue fixed in Zenker's solution seemed to show a significant decrease in MSA immunoreactivity, but no significant change for desmin staining was observed. None of the 154 normal tissues and 22 benign nonmyogenic tumors expressed MSA or desmin. Among 133 malignant nonmyogenic tumors, positive staining for both desmin and MSA was found in 3 of 8 cases of glioblastoma multiforme, 1 of 10 malignant schwannomas, and 1 of 14 malignant fibrous histiocytomas; staining for only MSA was found in 3 of 14 malignant fibrous histiocytomas, 1 of 10 malignant schwannomas, 6 of 6 fibromatoses, 1 of 1 mammary myofibroblastoma, and 1 of 7 malignant mesotheliomas; and staining for desmin only was seen in 1 of 7 malignant mesotheliomas. The authors conclude the following: (1) MSA is found consistently in muscle cells, pericytes, decidual cells, and myoepithelial cells, and frequently in myofibroblasts; (2) although the type of fixative does not influence the staining for desmin significantly, Zenker's fixative causes a marked decrease in the intensity of MSA staining; (3) both MSA and desmin are sensitive and specific markers for rhabdomyosarcoma; (4) for the diagnosis of formalin-fixed leiomyosarcomas, the sensitivities of MSA and desmin are roughly equal, but both are rather low; simultaneous staining for both antigens significantly increases the diagnostic yield but will not detect every case of leiomyosarcoma, especially those in the gastrointestinal tract; and (5) as many as 17% of nonmyogenic sarcomas display focal but unequivocal staining for MSA, desmin, or both.