Confirmation of the Prognostic Value of Foxp3+ Cells in Canine Mammary Tumors

SIMPLE SUMMARY: Foxp3+ cells have immunosuppressive properties that can interfere with beneficial anti-tumor immunity, enabling tumors to elude the host antitumor immune response. It has already been suggested that these cells play a role in canine mammary tumor progression, but the literature on this topic is poor. Our work aims to investigate Foxp3+ cells in 59 canine mammary tumors by immunohistochemistry and to evaluate associations with clinicopathological, immunohistochemical features, and overall survival (OS). Our findings confirm that the number of Tregs is significantly higher in canine mammary carcinomas than adenomas and that a high number of Foxp3+ cells were associated with negative prognostic factors and shorter overall survival (OS). ABSTRACT: Foxp3+ cell counts were evaluated by immunohistochemistry in 59 canine mammary tumors, 20 adenomas, and 39 carcinomas in three different compartments: intratumoral, within the adjacent stroma, and in the distant stroma. Foxp3+ lymphocyte counts were compared with histotype, grading, presence of lymphatic invasion, immunohistochemical expression of estrogen and progesterone receptors, expression of c-erbB-2, and the overall survival (OS). Our findings confirmed that Foxp3+ cells were significantly higher in canine mammary carcinomas compared to adenomas. A significantly higher number of Foxp3+ cells were detected in grade III carcinomas compared to grade II carcinomas, as well as in tumors with lymphatic invasion and loss of ER-expression. Finally, a high number of Foxp3+ cells was associated with poor prognosis. In conclusion, our findings highlighted the association of Foxp3+ lymphocytes with negative clinicopathological features and shorter overall survival (OS), thus confirming the role of Tregs as a negative prognostic marker in canine mammary carcinomas.