Intratumoral FoxP3 expression is associated with angiogenesis and prognosis in malignant canine mammary tumors

• We studied Intratumoral FoxP3 immunoexpression and its association with angiogenesis and survival in canine malignant mammary tumours.
• We found the highest FoxP3 immunoexpression associated with angiogenesis (High levels of VEGF and Microvascularization density).
• In malignant tumours, higher Intratumoral FoxP3 immunoexpression is related with poor prognosis both in univariate and multivariate survival analysis.

The activity of regulatory T cells (Tregs) is closely associated with the expression of FoxP3 transcription factor. FoxP3 regulatory T cells (FoxP3Treg) have immunosuppressive properties and can work for prevention of harmful autoimmune responses, however can also interfere with beneficial anti-tumor immunity. In human breast cancer these cells play a crucial role in tumor progression. In canine mammary tumors (CMT) this topic is not well-documented. This study included 80 malignant CMT and studied, by immunohistochemistry, the intratumoral FoxP3 expression together with microvessel density (MVD), vascular endothelial growth factor (VEGF) and several clinicopathological characteristics. Abundant FoxP3Treg cells were associated with tumor necrosis (p = 0.001), high mitotic grade (p < 0.001), more marked nuclear polymorphism (p = 0.001), poor differentiation of tumors (p < 0.001), high histological grade of malignancy (HGM) (p < 0.001), presence of neoplastic intravascular emboli (p < 0.001) and presence of lymph node metastasis (p < 0.001). Intratumoral FoxP3 was correlated with MVD (r = 0.827; p < 0.001) and associated with VEGF (p = 0.001). Additionally tumors with abundant FoxP3Treg cells were associated with shorter overall survival (OS) time in univariate and multivariate analysis (p < 0.001 Kaplan–Meier curves and 7.97 hazard ratio, p < 0.001 Cox proportional hazard model). Results suggest that Treg cells play a role in CMT progression and may contribute to increased angiogenesis and aggression in these tumors. The association of intratumoral FoxP3 expression with shorter OS in multivariate analysis suggests the usefulness of Treg cells as an independent prognostic marker.