Medullary carcinoma of breast: an immunohistochemical study of its lymphoid stroma.

Immunoperoxidase staining for IgA, IgG, IgM, and secretory component (SC) was performed on ten cases each of medullary carcinoma and infiltrating duct carcinoma of breast. Plasma cell-rich stroma of medullary carcinoma was found to contain predominantly IgA plasma cells. Tumor cells also contained IgA and SC. In contrast, the few plasma cells of infiltrating duct carcinoma were found to be predominantly IgG type, and the tumor cells contained none or very small amounts of IgA and SC. Because the presence of IgA plasma cells and IgA and SC in lining epithelial cells are characteristic features of organs of the secretory Ig system, these findings in medullary carcinoma may suggest a good degree of functional differentiation of these tumor cells and correlate well with the well-known favorable prognosis associated with this tumor.