Results from the IVW method indicated that CD45RA- CD4+ %CD4+ significantly decreased the risk of breast cancer (mature stages of T cells panel; Odds ratio: 0.9140, 95%CI: 0.8810 - 0.9480, p-value: 1.37×10−6), and this was corroborated by the weighted mode (Odds ratio: 0.9498, 95%CI: 0.9084 - 0.9931, p-value: 0.0471) and MR-Egger method (Odds ratio: 0.8747, 95%CI: 0.8114 - 0.9430, p-value: 0.0068). Here, CD4 is linked to breast cancer.