Double immunohistochemical labeling technique applied to different types of cytokeratins in epithelial proliferations of the breast

Luminal cytokeratin expression profiles of breast papillomas and papillary carcinomas and the utility of a cytokeratin 5/p63/cytokeratin 8/18 antibody cocktail in their distinction

Luminal cytokeratin (CK) expression in breast papillary lesions, and its potential diagnostic utility among other markers in distinguishing between papillomas and papillary carcinomas, has not been previously evaluated. Such expression was determined in 42 papillary lesions (18 papillary carcinomas and 24 papillomas) by immunostaining with a CK5/p63/CK8/18 antibody cocktail. The mean CK8/18 intensity score and percentage of positive cells were significantly higher in papillary carcinomas (227 and 95%, respectively, vs 86 and 42% in papillomas; both P-values <0.0001), whereas the mean CK5 intensity score and percentage of positive cells were significantly lower (7 and 5%, respectively, vs 107 and 58% in papillomas; both P-values <0.0001). Half (9/18) of the papillary carcinomas expressed p63 vs all (24/24) of the papillomas (P = 0.0001). P63 expression in papillary carcinoma was always (9/9; 100%) focal/limited in nature (expression in <10% of cells), whereas focal expression was seen in only four (17%) papillomas (P<0.0001). Both differential CK (CK8/18 and CK5) expression and p63 were equally sensitive (100%) for the diagnosis of papillary carcinoma, but differential CK expression was more specific (96 vs 83%), resulting in a greater accuracy. However, the best discriminatory power in the distinction from papilloma was achieved when all three markers were used in combination, resulting in 100% sensitivity and specificity values. It is concluded that breast papillary lesions have differential CK expression profiles that, especially in combination with p63, can be useful for their stratification, potentially also in needle biopsy material, in which more accurate and reproducible characterization is needed.

Methylation of CpG islands of p16(INK4a) and cyclinD1 overexpression associated with progression of intraductal proliferative lesions of the breast

P16(INK4a) is a tumor suppressor gene frequently inactivated by aberrant promoter hypermethylation. In this study, p16(INK4a) methylation was evaluated in intraductal proliferative lesions of the breast, using real-time quantitative polymerase chain reaction (MethyLight) and methylation-sensitive restriction endonuclease polymerase chain reaction. Immunohistochemistry was performed to compare and validate the methylation analysis. P16(INK4a) methylation associated with oncogene cyclinD1 expression, detected through the use of in situ hybridization and immunohistochemistry, was likewise characterized. P16(INK4a) methylation displayed varying significance among different types of intraductal proliferative lesions. Both the positive rate and the median quantitative methylation value increased with the evolution of intraductal proliferative lesions through the use of quantitative and qualitative assays. P16(INK4a) methylation was positively correlated to cyclinD1 overexpression. This study demonstrated that p16(INK4a) methylation served as the silencing mechanism of p16(INK4a) protein expression and played a crucial role in the intraductal proliferative lesions' progression. In the differential diagnosis of intraductal proliferative lesions, quantitative DNA methylation analysis of p16(INK4a) by MethyLight may be used as a surrogate, especially to distinguish atypical ductal hyperplasia from usual ductal hyperplasia and low-grade ductal carcinoma in situ. Furthermore, this study discovered that flat epithelial atypia do not share similar molecular profiles of p16(INK4a) epigenetic modification with atypical ductal hyperplasia and low-grade ductal carcinoma in situ.