OBJECTIVETo determine the differential diagnostic value of high molecular cytokeratin 34betaE12 as a benign marker in mammary lesions.

METHODS90 cases (30 benign non-proliferative diseases, 20 benign proliferative diseases, 10 intraductal carcinomas and 30 invasive carcinomas) were collected, all of which had undergone fine needle aspiration cytology (FNAC) examination and a follow-up operation. Immunohistochemical staining was performed using monoclonal antibodies against 34betaE12 on FNAC smears and the follow-up paraffin sections. SPSS 10.0 software was applied to analyze the differential diagnostic value of 34betaE12 in benign and malignant mammary lesions.

RESULTS(1) No significant difference was found in the expression of 34betaE12 between benign non-proliferative and proliferative disease. (2) A significant difference was found between the expression of 34betaE12 in mammary benign disease and mammary carcinoma. 66.7% and 66.3% of the carcinoma cases showed either lack of 34betaE12 expression or had only a few isolated 1+ cells which were cytoplasmic positive for 34betaE12 immunoreaction on FNAC smear and paraffin section respectively. The remaining 33% of cases having 2+ to 3+ cells mainly displayed cytoplasmic granular positive reaction rather than strong membranous and cytoplasmic positive reaction as benign lesions. In contrast with carcinoma, most benign lesions showed strong immunoreaction of 2+ to 3+ and especially exhibited complete strong membranous and cytoplasmic positive reaction on paraffin section, their positive expressive character differed from those of carcinoma. The positive rates on FNAC smear and paraffin section were 100% and 78% respectively. (3) Certain types of intraductal carcinoma, including low grade cribriform, papillary and solid type either lacked 34betaE12 expression or revealed a few isolated 1+ cells with cytoplasmic positivity for 34betaE12 immunoreaction. Pronounced immunoreaction of 3+ was only seen in high grade comedotype intraductal carcinoma.

CONCLUSIONS34betaE12 may serve as a marker of benign mammary disease for differential diagnosis. When there is a total or predominant lack of 34betaE12 expression, the possibility of carcinoma should be strongly considered. If 34betaE12 is expressed diffusely in the suspicious area with a strong membranous staining in particular, a benign proliferative process rather than carcinoma must be considered.