ESR1 and thyroid cancer: The results of this univariate Cox regression showed that age, ethnicity, marital status, primary tumor location, molecular typing, PR status, ER status, whether radiotherapy, whether chemotherapy, T stage, N stage, M stage were the factors affecting the secondary thyroid cancer in breast cancer patients; while the results of multivariate Cox regression showed that age, race, whether radiotherapy, primary tumor location, N-stage, and M-stage were independent risk factors affecting the development of thyroid cancer in patients with breast cancer, and the results are shown in Table 4.