However, we did not identify any relationship between breast cancer and insulin levels (SMD = 0.22, 95% CI = -0.06-0.50, I<sup>2</sup> = 97.3%).<h4>Conclusion</h4>This meta-analysis demonstrated that C-peptide levels were positively related to breast cancer in women, and no relationship between insulin levels and breast cancer was found. The gene discussed is INS; the disease is breast cancer.