Current practical applications of diagnostic immunohistochemistry in breast pathology.

In recent years, immunohistochemistry has assumed an increasingly prominent role in diagnostic breast pathology. Immunohistochemistry is now frequently used in the evaluation of many epithelial proliferations of the breast. Common applications include the use of myoepithelial markers to evaluate for stromal invasion, E-cadherin to distinguish between ductal and lobular neoplasia, high molecular weight cytokeratins to differentiate usual ductal hyperplasia from ductal carcinoma in situ, immunohistochemical profiles to characterize site of origin of metastatic carcinomas, and cytokeratin stains to detect metastases in sentinel lymph nodes. Recent advances, practical considerations, and potential pitfalls in the use of immunohistochemistry in these five diagnostic categories are discussed herein.