The prognostic variability recorded within homogeneous groups of patients for anatomo-clinical disease stages has led to a more detailed biological characterization of breast cancer. Recently, the attention of the scientific community has focused on the role of tumor-infiltrating lymphocytes (TILs). Therefore, the need of an in-depth immunomorphological characterization of TILs has been emerged. The presence of TILs has been retrospectively investigated in 113 female cases of ductal carcinoma. An immunohistochemical investigation with CD3, CD4, CD8, CD20, CD56, granulysin, perforin-1, granzyme-B and TIA-1 was performed according to the standard procedures on all 17 cases with TILs evidence. TILs consisted of T and B lymphocytes: the prevalent population showed a T immunoprofile with a CD8-immunopositive killer subpopulation (Tk), close-linked to carcinomatous cells, and a CD4-immunopositive helper subpopulation (Th), inside the tumor. A time sequence (firstly T, then B) has been disclosed. Granulysin, perforin, granzyme-B and TIA-1 were expressed by Tk cells. The activated Tk cells secrete these mediators as a result of the binding to the tumor target cell, causing its lytic planned death. The cytotoxicity supported by Tk cells appears an important favorable prognostic factor. Therefore, a graduation system for TILs in breast cancer has been here proposed (absent, non-brisk, brisk).