CD8+ lymphocytes and apoptosis in typical and atypical medullary carcinomas of the breast

Abstract

Medullary breast carcinoma (MBC) is a form of ductal invasive carcinoma (DIC) characterized by an abundant infiltration of the tumour by lymphocytes. MBC has been classified histologically into typical medullary carcinoma (TMC) and atypical medullary carcinoma (AMC), with TMC having a better prognosis than AMC and other DIC. The distribution of CD8+ lymphocytes within tumour nests and lymphocyte tracts, and apoptosis in lymphocytes and tumour cells within tumour nests, were studied in archived formalin fixed and paraffin embedded tissues of TMC and AMC. CD8+ lymphocytes tend to accumulate along the margins of lymphocyte tracts that adjoin tumour nests. There were significantly more CD8+ lymphocytes within tumour nests of TMC than AMC. TMC also tended to have more CD8+ lymphocytes within lymphocyte tracts than AMC. Apoptosis of lymphocytes in contact with tumour cells and of tumour cells in contact with lymphocytes was observed in both AMC and TMC within tumour nests but differences in the proportions of apoptotic tumour cells and lymphocytes between the two tumour types could not be established. The findings are consistent with CD8+ cytotoxic lymphocyte-mediated immunity contributing to the more favourable prognosis for TMC compared to AMC.