HLA-DR and beta(2) microglobulin expression in medullary and atypical medullary carcinoma of the breast: histopathologically similar but biologicallydistinct entities

Aims-To examine the expression of HLA-DR and beta(2) microglobulin in medul lary carcinoma and atypical medullary carcinoma of the breast to determine if the effective presentation of tumour antigens to the immune system can d ifferentiate between these two histopathologically similar entities. Methods-Expression of HLA-DR and PL microglobulin was examined by immunohis tochemical methods in five samples of medullary carcinoma of the breast, wh ich has a relatively favourable prognosis, six samples of atypical medullar y carcinoma of the breast, which has a prognosis closer to that of regular invasive duct carcinoma, and 20 samples of invasive duct carcinomas, 10 wit h an accompanying lymphocytic infiltrate. Results-A positive and significant correlation was found between tumour typ e and both HLA-DR and beta(2) microglobulin expression. Expression was most prominent in medullary carcinoma, followed by atypical medullary carcinoma and invasive duct carcinoma with and without lymphocytic infiltrates. The mean intensity and percentage of HLA-DR tumour immunostaining were signific antly higher in medullary carcinoma than in the other three tumour groups, as was the mean intensity of beta(2) microglobulin immunostaining. Mean per centage of beta(2) microglobulin immunostaining was significantly higher in medullary carcinoma than in invasive duct carcinoma without lymphocytic in filtrates, and showed a trend to increase from invasive duct carcinoma with lymphocytic infiltrates to atypical medullary carcinoma and medullary carc inoma. Conclusions-Medullary carcinoma and atypical medullary carcinoma of the bre ast differ in their expression of HLA-DR and beta(2) microglobulin. The rel atively favourable prognosis of medullary carcinoma of the breast may be re lated to effective tumour antigen presentation to the immune system through MHC-I and MHC-II expression. Immunotherapy aimed at MHC-I and MHC-II induc tion might have a beneficial effect in breast cancer.