Possible significance of differences in proportions of cytotoxic T cells and B-lineage cells in the tumour-infiltrating lymphocytes of typical and atypical medullary carcinomas of the breast.

Medullary carcinoma (MC) of the breast is a high grade carcinoma that has a relatively favourable prognosis compared to atypical medullary carcinoma (AMC) and other more common breast carcinomas. In a retrospective study in Brunei Darussalam of all available biopsy samples, we compared the nature of the tumour-infiltrating lymphocytes (TILs) in MC and AMC in relation to recorded tumour characteristics. CD4, CD8, CD20, CD25, CD45RO, and CD56 and common tumour biomarkers were detected immunohistochemically. The 11 cases of MC had no nodal metastases and survived without relapse, suggesting good tumour control. In contrast, 7 cases of nodal metastases and 1 relapse were observed in 12 AMCs. Although not statistically significant, there was a tendency for a greater proportion of AMCs to express the Her2/neu oncogene. Higher proportions of CD45RO+ and CD8+ cells, and lower levels of CD20+ cells, were characteristic of TILs in MC compared to AMC. The ratio of CTL to B-lineage cells in TILs in both tumours considered together was inversely related to the expression of HER2/neu and the presence of nodal metastases. The findings suggest that CTLs, rather than antibodies, may give better tumour control in MC relative to AMC. We propose that a comparison of the cellular, molecular and immunological characteristics of MC and AMC, as a paired model system, in a multi-centre investigation with a much larger number of samples will be valuable for better understanding mechanisms of tumour immunity.