When we considered risk factors for second primary corpus uteri cancer after breast cancer (Table 3), the risk of second primary corpus uteri cancer was positively associated with the age at first cancer (46–55 vs. ≤ 45 years, aHR = 2.343, P < 0.001; 56+ vs. ≤ 45 years, aHR = 3.218, P < 0.001) (Fig. 1a), race (black vs. white, aHR = 1.142, P = 0.042), and PR status (positive vs. negative, aHR = 1.131, P = 0.043) (Fig. 1b), while an inverse association was found with the year of first cancer, and ER status showed no association with risk (P = 0.293). This evidence concerns the gene PGR and breast cancer.