Mononuclear cells in malignant and benign human breast tissue.

The mononuclear cell infiltrate in benign and malignant breast tissue was studied using monoclonal antibodies with an immunoenzymatic technique. Infiltrating duct carcinomas contained a mononuclear cell infiltrate made up mostly of T lymphocytes, with minor B-cell and macrophage populations. The most preponderant T-cell subset was the T8, cytotoxic-suppressor cell. Some tumors contained T6-positive cells, possibly immature T cells. In contrast, stromal lymphocytes in benign fibrous mastopathy were largely T cells, but the T4, helper-inducer cell was the most preponderant, and T6 cells were not detected. Intraepithelial lymphocytes were identified in benign breast tissue. Intraepithelial lymphocytes are T cells, with a great preponderance of the T8 phenotype. The T6-positive cells were also identified within the epithelium, but they seemed to represent myoepithelial cells rather than immature T cells.