Medullary carcinoma (MC) of the breast is characterized by large anaplastic cells and infiltration by benign lymphocytes. Patients with this pattern of
breast carcinoma are considered to have a better prognosis than those with other histological subtypes. We reviewed cases of primary
breast carcinoma that were surgically resected between 1990 and 2004. Of these, 13 cases of
medullary carcinoma of the breast with lymphocyte infiltration were reported. Tests for CD3, CD4, CD8, CD20, CD56, TIA-1, and
granzyme B were performed on
paraffin sections. We found that the MC contained very few NK cells, as assessed by their reactivity with the CD56
antibodies. However, MC had a significantly greater percentage of CD3, CD8, TIA-1, and
granzyme B lymphocytes infiltrating the stroma of the
tumor. Furthermore, more CD8-positive than CD4-positive T-cell lymphocytes were present within the
tumor cell nests in MC, as opposed to the proportion in usual
ductal carcinoma. The infiltrating cytotoxic/suppressor T cells in MC represent host resistance against
cancer, and the high grading of the T-cell infiltration could explain, in part, a key mechanism controlling the good prognosis for this type of
tumor and solve the pathological paradox of MC.