The risk of endometrial cancer was higher in the tamoxifen group than in the control group (hazard ratio [HR], 3.77; 95% CI, 3.04-4.66) after adjusting for age, body mass index, history of diabetes, hypertension, dyslipidemia, polycystic ovary syndrome, GnRH agonist treatment, and trastuzumab treatment. The gene discussed is GNRH1; the disease is polycystic ovary syndrome.