At multivariate logistic regression analysis, which was carried out in order to predict breast cancer with a low Ki67 index inferior to 20%, only endometriosis was a significant predictive factor for cancer with a lower Ki67 index, p = 0.010 (OR = 3.3882; 95%CI: 1.354–11.135). The gene discussed is MKI67; the disease is breast carcinoma.