Smooth Muscle-Myosin Heavy Chain (SM-MHC) is a cytoplasmic structural protein that is a major component of the contractile apparatus in smooth muscle cells. Expression of smooth muscle myosin is developmentally regulated, appearing early and is specific for smooth muscle development. SM-MHC stains the intact myoepithelial cell (MEC) layers present in benign and in situ malignant breast and bronchioloalveolar lesions and is therefore very helpful in distinguishing between benign and malignant tumors. Studies have shown that Calponin, SM-MHC and p63 labeled MECs in intraductal and micropapillary DCIS cases while invasive papillary carcinomas (IC) were uniformly negative for all cases. Staining with p63 was discontinuous, making interpretation difficult. Calponin was more sensitive and intense than SM-MHC but less specific exhibiting cross-reactivity with myofibroblastic cells. Although CD10 can aid in the distinction between IC and DCIS, SM-MHC is a more sensitive and specific marker of MEC and shows less heterogeneity of immunostaining pattern. SM-MHC also reacts with visceral and vascular smooth muscle cells.
1. Nicolas MM, et al. Pleomorphic and dedifferentiated leiomyosarcoma:
clinipathologic and immunohistochemical study of 41 cases. Hum Pathol. 2010 May;
2. Hilson JB, et al. Phenotypic alterations in myoepithelial cells associated with benign
sclerosing lesions of the breast. Am J Surg Pathol. 2010 Jun; 34(6):896-900.
3. Saad RS, et al. Distribution of basal/myoepithelial markers in benign and malignant
bronchioloalveolar proliferations of the lung. Appl Immunohistochem Mol Morphol.
2010 May; 18(3):219-25.
4. Hill CB, Yeh IT. Myoepithelial cell staining patterns of papillary breast lesions:
from intraductal papillomas to invasive papillary carcinomas. Am J Clin Pathol. 2005
5. Kalof AN, et al. Immunostaining patterns of myoepithelial cells in breast lesions: a
comparison of CD10 and smooth muscle myosin heavy chain. J Clin Pathol. 2004 Jun;
6. Center for Disease Control Manual. Guide: Safety Management, NO. CDC-22,
Atlanta, GA. April 30, 1976 “Decontamination of Laboratory Sink Drains to Remove
7. National Committee for Clinical Laboratory Standards (NCCLS). Protection of
laboratory workers from infectious diseases transmitted by blood and tissue; proposed
guideline. Villanova, PA 1991; 7(9). Order code M29-P