Keratin 19 in paraffin sections of medullary carcinoma and other benign and malignant breast lesions.

This investigation was aimed at studying the distribution of keratin 19 in various histological types of invasive breast carcinoma and benign breast lesions using two different antibodies, comparing the results, and assessing the significance of the finding. In particular, the usefulness of using the absence of keratin 19 immunostaining as a marker for medullary carcinoma was examined. Paraffin sections of 49 invasive breast carcinomas and 40 benign lesions were examined by the avidin-biotin complex immunoperoxidase technique using two commercially available keratin 19-specific monoclonal antibodies, BA17 and RCK 108. The results showed that the latter antibody stained more cases and the intensity of its staining was more pronounced than BA17. Most medullary and poorly differentiated invasive ductal carcinomas were BA17 negative and RCK108 negative or weakly positive. Moderately and well-differentiated ductal, invasive lobular, tubular, and most mucinous carcinomas were mostly positive with both antibodies, whereas a case of signet ring and a case of spindle cell carcinoma were negative with the two antibodies. Thirty eight of the 40 benign lesions examined showed variable numbers of positive cells, reflecting in general the pattern seen in normal ducts and acini. It is concluded that although keratin 19 seems to be completely absent or at most only weakly represented in paraffin sections of medullary carcinoma, similar reactions are obtained with poorly differentiated ductal tumors. Different antibodies may give different reactions, but well-differentiated ductal and invasive lobular tumors are usually more strongly stained, whereas signet ring and spindle cell carcinomas seem to be negative.(ABSTRACT TRUNCATED AT 250 WORDS)