An evaluation of the clinical significance of FOXP3+ infiltrating cells in human breast cancer

Studies in mice have shown that thymic-derived CD4+ CD25+ regulatory T cells (T reg; FOXP3 + lymphocytes) inhibit an antitumour immune response. Additional studies have also reported that the T reg population increases in peripheral blood and tumour tissues from patients with cancer. However, the relationship between the T reg population and the patient prognosis remains controversial. Our aim was to determine the prognostic value of T reg cell density in breast cancer using immunohistochemical assessment of FOXP3, which has been shown to be the optimal marker for T regs. Tissue microarrays were used, and the density of FOXP3 + cells was determined in a series of 1445 cases of well-characterised primary invasive breast carcinoma cases with long-term follow up. FOXP3 + cell numbers were counted in tumour nests, in tumour-adjacent stroma, and in distant stroma. The total number of FOXP3 + cells significantly correlated with higher tumour grade ( r s = 0.37, P