Expression of MHC class I and class II antigens in primary breast carcinomas and synchronous nodal metastases.

Expression of the major histocompatibility (MHC) class I and class II antigens was studied by immunohistochemistry in a series of 70 primary breast carcinomas and in nodal metastases. In particular, the expression of class I (HLA A-B-C) and class II (DP, DQ and DR) molecules was compared in: a) primary breast cancers devoid of nodal metastases (n = 36) and tumors exhibiting metastatic deposits (n = 34) at the time of surgery, and b) primary breast carcinomas and their corresponding synchronous axillary nodal metastases. Reduced or absent HLA A-B-C antigen expression was seen in approximately 54.3% of primary breast carcinomas, whereas a partial or complete induction of class II products was observed in 18.5% (DQ), 30% (DP) or 48.5% (DR) of the same cases. An almost complete overlap of antigen expression was observed in breast tumors in which no metastases were found by histological examination of axillary nodes and in neoplasms showing histologically-diagnosed synchronous metastases. The reactivity for class I and class II antigens in nodal metastases roughly paralleled that exhibited by corresponding primary tumors. A discordant expression was seen in 11 cases (32%) stained for HLA A-B-C and in 8 (24%), 7 (21%) and 6 (18%) cases assayed for DP, DQ and DR products, respectively. When a discordant expression was detected, either decreased or increased staining patterns were observed in metastases. The finding of overlapping MHC antigenic profiles in the majority of primary breast tumors and nodal metastases casts doubts on the hypothesis that loss of MHC antigens can play an important role in the seeding and growth of metastatic breast carcinoma cells.