Immunohistochemical characterization of molecular subtypes of invasive breast cancer: a study from North India

In recent years breast cancer has been classified on the basis of its molecular characteristics by gene expression profiling. A similar classification using immunohistochemistry has been identified so that it has a wider application. This study was designed to define the precise prevalence of molecular subtypes of invasive breast carcinoma using immunohistochemistry in patients from north India and to correlate it with known clinical and histological prognostic factors. Based on ER/PR/Her2/neu expression, 100 cases of invasive breast cancer were categorized into: ER+ and ⁄ or PR+ and Her2/neu- (47%), ER+ and⁄or PR+ and Her2/neu+ (15%), ER- and ⁄ or PR- and Her2/neu+ (Her2/neu overexpressing, 21%), ER-, PR- and Her2/neu- (Triple negative, 17%). All cases demonstrated positivity for the luminal Cytokeratins 8/18. In addition, 10% of these tumours showed expression of the basal markers (CK4/14, CK5/6). Among the 17 triple negative cases, eight cases were positive for one of the basal markers and two cases with basal marker expression were Her2/neu overexpressing. The basal markers showed significant correlations only with histological grade and ER negative status. On the basis of hormone receptor, Her-2/neu and cytokeratin expressions, distinct subclasses of breast cancer have been identified which show significant differences in relation to histological grade and ER status. Expression of basal markers is needed to define basal-like breast cancer.