Immunohistochemistry in the diagnosis of papillary lesions of the breast.

AIMS: Many immunohistochemical markers have been studied for differentiating papillary lesions. However, their differentiating power has not been evaluated comprehensively. Additionally, assessment of some markers will require the difficult task of identifying different cell types. In the current study, we aimed to devise a simple papillary panel which can aid in diagnosis irrespective of architectural pattern and cell type differentiation. METHODS AND RESULTS: Immunohistochemical analysis of papillary lesions using myoepithelial markers [p63 and smooth muscle actin (SMA)], high molecular weight cytokeratins (HMWCKs: CK5, CK5/6, CK14 and 34ßE12), hormone receptors (ER and PR) and neuroendocrine markers (chromogranin and synaptophysin) was performed. Among them, neuroendocrine markers showed high specificity but low sensitivity. HMWCK specificity was better than that for myoepithelial markers. Homogeneous staining pattern for hormonal receptors rather than their percentage positivity was more effective in identifying malignant lesions. Negative staining for two or more of HMWCKs, namely CK5/6, CK14 and 34ßE12, achieved the best overall specificity and sensitivity of 87.8% and 94.1%, respectively, irrespective of the architecture. Their discriminatory power was validated with an independent cohort of core needle biopsies. CONCLUSIONS: A marker panel with HMWCKs could be used in differentiating papillary lesions irrespective of architectural pattern or cell type differentiation.