This study intends to detect the levels of peripheral blood lymphocyte subsets (CD3 + T cells, CD3+/CD4 + T cells, CD3+/CD8 + T cells, CD4+/CD8 + ratio, natural killer (NK) cells, and B cells) in breast cancer patients before RT to understand the immune function of patients and investigate the impact of immune status on the severity of ARD. This evidence concerns the gene CD4 and breast cancer.