Accumulation of regulatory T cells in sentinel lymph nodes is a prognostic predictor in patients with node-negative breast cancer.

It has been revealed that sentinel lymph nodes (SLNs) from patients with node-negative breast cancer involve RT-PCR detected micrometastases and isolated tumour cells. However, the prognostic significance of the pathologically undetectable micrometastases is still controversial. In this study, we evaluated Foxp3 positive regulatory T cells (Treg) in SLNs as host-side immune marker that has the potential to detect these micrometastases. In the analyses of training set (n=30), elevated Treg was strongly associated with the pathologically undetectable micrometastases. In the analyses of validation set (n=129) in patients with node-negative, relapse-free survival in patients with elevated Treg was significantly shorter than those with lower Treg (p=0.005). Furthermore, in multivariate analyses, elevated Treg was correlated with relapse-free survival (p=0.012). Our data indicate that Treg may increase in the microenvironment of SLNs along with pathologically undetectable micrometastases and is a prognostic predictor in patients with node-negative breast cancer.