The role of immunohistochemistry in the differential diagnosis of breast lesions.

Immunohistochemistry may be helpful in the diagnosis of various breast lesions. It can be used to assist in distinguishing benign and malignant conditions, or to clarify the histological subtype of invasive carcinomas. There are several markers relatively frequently utilised. Myoepithelial markers (p63, alpha-SMA, smooth muscle myosin heavy chain, and others) are useful to highlight myoepithelial cells. They are employed to verify myoepithelial cell lining in intraductal papillary lesions, or to recognise peripheral myoepithelial cells for non-invasive carcinoma, although their staining results are not always excellent. High molecular weight cytokeratins (CK5/6, CK14, 34betaE12) typically show a mosaic-like pattern of expression in benign papillary/hyperplastic lesions, and are mostly negative in ductal in situ carcinoma, but some exceptions exist. Neuroendocrine differentiation (confirmed by anti-chromogranin A or synaptophysin) suggests malignancy in solid and papillary intraductal epithelial proliferations. The significance of immunohistochemical evaluation of apocrine lesions is still controversial. Negative E-cadherin staining is used for making confirmative diagnosis of lobular carcinoma, with a specificity and sensitivity of approximately 90%. Cytokeratins, especially the antibody 34betaE12, are of value to differentiate spindle cell carcinoma from phyllodes tumour. There are some other useful markers for characterising certain histological subtypes. Nevertheless, for accurate diagnosis, it is essential to correlate the immmunohistochemical staining results with the histological findings.