Medullary carcinoma of the breast. Identification of lymphocyte subpopulations and their significance.

Fifty-two infiltrating breast carcinomas with medullary features (BCMF) were studied immunohistochemically to determine the immunophenotype of the mononuclear tumor inflammatory cells (MTIC) in formalin-fixed, paraffin-embedded material. The neoplasms were also examined for Epstein-Barr virus (EBV) DNA by the polymerase chain reaction (PCR). BCMF were independently classified as medullary carcinoma (MC) or infiltrating ductal carcinoma (IDC) by six observers according to the criteria of Pedersen et al. DNA from 35 BCMF was successfully amplified using PCR, but all were negative for EBV DNA. These included, by 4/6 consensus diagnosis, 16 MC, 18 IDC, and one BCMF which failed to achieve consensus diagnosis. MTIC were present to a mild degree in 19 BCMF (37%) and to moderate to severe degrees in 33 (63%). MTIC were predominantly (> or = 75%) lymphocytic in 31 BCMF (13 MC, 16 IDC, two without consensus diagnostic agreement), and plasmacytic in 10 (six MC, four IDC); equal proportions of lymphocytes and plasma cells occurred in 11 (six MC, five IDC). Lymphocytic MTIC were mostly CD45RO+/CD3+ T-cells in nearly all cases, and showed a predominant CD3+/CD4+ and CD3+/CD4- immunophenotype in 36% and 64% of cases, respectively. Natural killer cells (CD57+) and histiocytes (MAC 387+) were virtually absent. The number, cell type, and T-cell subsets of the MTIC were unrelated to consensus diagnosis, axillary lymph node status, or overall survival. EBV is unassociated with MC, despite the histologic similarities of MC to EBV-associated lymphoepithelial lesions of other organs.(ABSTRACT TRUNCATED AT 250 WORDS)