By Rodney T. Miller, Director of Immunohistochemistry
As all surgical pathologists know, the distinction of invasive breast lesions from certain types of noninvasive lesions can be a difficult one, particularly on small needle biopsy samples. Studies have shown that invasive breast carcinoma lacks an associated myoepithelial layer on the periphery of the invasive nests of tumor cells, although this layer is intact or partially intact in benign lesions and CIS. Therefore, identification of an intact or partially intact myoepithelial layer in a breast lesion provides supportive evidence of a noninvasive process. In the past, smooth muscle actin (SMA) was often used for this purpose, but due to the extensive cross reaction of SMA with myofibroblasts, interpretation of SMA immunostains in a number of these types of cases was problematic.
Fortunately, there are several new markers of myoepithelial cells available (smooth muscle myosin heavy chains and calponin), that do not suffer from this problem (Fig. 1), and for this reason they are extremely useful as aids in the interpretation of certain difficult breast biopsies. Below is an example of a case where immunostains for smooth muscle myosin allowed a confident interpretation of a problematic case to be rendered.
Case Study 46 year-old female with a mammographic lesion underwent stereotactic needle biopsies of the breast. Pathologic examination revealed a background of fibrocystic change, and one focus that raised the possibility of tubular carcinoma (Fig. 2).
These new markers have been found to aid in the following differential diagnostic problems:
— Radial Scar vs. Infiltrating Tubular Carcinoma
— Cancerization of Sclerosing Adenosis by DCIS (mimicking invasive carcinoma)
— Invasive Cribriform Carcinoma vs. DCIS
— Adenoid Cystic Carcinoma vs. Collagenous Spherulosis or Cribriform DCIS
— Papillary Carcinoma vs. Papilloma
— Nipple Adenoma vs Infiltrating carcinoma.
1.Yaziji H, Gown, Am, Sneige N: Detection of Stromal Invasion in Breast Cancer: The Myoepithelial Markers. Advances in Anatomic Pathology 7 (2): 100-109, 2000.
2.Wang NP Wan BC, Skelly M et al: Antibodies to Novel Myoepithelium-Associated Proteins Distinguish Benign Lesions and Carcinoma Insitu from Invasive Carcinoma of the Breast. Applied Immunohistochemistry 5 (3): 141-151, 1997.