ObjectiveTo investigate the correlation between abnormal thyroid function and benign or malignant breast tumors. MethodsThe contents of free iodine three original acid (FT3), three iodine original acid (T3), thyroxine (T4), free thyroxine (FT4), thyroid-stimulating hormone (TSH), anti-thyroglobulin antibodies (Anti-TG), and antithyroid peroxidase antibody (Anti-TPO) were detected by chemiluminescence method in 563 patients with benign breast neoplasms, 87 patients with breast cancer, and 123 health examination population. ResultsT3 and T4 levels in patients with breast cancer were lower than those of normal control group and benign tumor group (P < 0.05). However, there were no significant difference in the levels of FT3, FT4, and TSH between the 3 groups (P > 0.05). The positive rates of Anti-TPO and Anti-TG were higher than those of benign group and normal group (P < 0.001). T3 and T4 levels in patients with breast cancer were not related to the expression of ER and PR, in Her-2 negative expression and lymph node metastasis were relatively low (P < 0.05). ConclusionThe decrease of contents of T3 and T4, and the positive expressions of Anti-TPO and Anti-TG may provide a basis for predicting the incidence of breast cancer.