Immunosuppressive regulatory T cells are associated with aggressive breast cancer phenotypes: a potential therapeutic target

FoxP3 is a marker for immunosuppressive CD25+CD4+ regulatory T cells. These regulatory T cells are thought to play a role in inducing immune tolerance to antigens and may be selectively recruited by carcinomas. We investigated whether breast carcinomas had significant numbers of FoxP3-positive regulatory T cells by immunohistochemistry, and if their presence was associated with other prognostic factors, such as Nottingham grade, hormone receptor immunohistochemical profile, tumor size, or lymph node metastases. Ninety-seven needle core or excisional breast biopsies with invasive breast carcinoma diagnosed at the University of Washington were stained with antibodies to FoxP3, estrogen receptor, and Her2/neu. The numbers of FoxP3-positive cells present within the neoplastic epithelium, and immediately adjacent stroma were counted manually in three high-powered fields (HPFs; x 400) by two independent pathologists. The average scores were then correlated with the parameters of interest. A threshold of >= 15 FoxP3-positive cells/HPF was used to define a FoxP3-positive case in some analyses. Higher average numbers of FoxP3-positive cells present significantly correlated with higher Nottingham grade status (P = 0.000229). In addition, the presence of significant numbers (>= 15/HPF) of FoxP3-positive cells in breast carcinoma was positively associated with higher Nottingham grade (P = 0.00002585). Higher average numbers of FoxP3-positive cells were also significantly associated with larger tumor size (>2.0 cm; P = 0.012824) and trended toward an association with estrogen receptor negativity. Interestingly, 'triple-negative' (estrogen and progesterone receptor negative and Her2/neu negative) Nottingham grade III cases were also significantly associated with high numbers of FoxP3 cells. These results argue that regulatory T cells may play a role in inducing immune tolerance to higher grade, more aggressive breast carcinomas, and are a potential therapeutic target for these cancers.