Abstract: Thyroid hormones and the related antibodies have some function in the natural process of breast cancer development. The possible mechanisms include: iodine complex can inhibit breast cell proliferation and can induce apoptosis; thyroid hormone can affect breast cancer cell proliferation and apoptosis; the imbalance of thyroid hormone and estrogen hormone promotes breast cells cancerous; hypothyroidism may affect the proliferation and invasiveness of breast tumors; lymphocytic infiltration or abnormal local immune response in thyroid disease.

Key words: Breast neoplasms, Thyroid neoplasms, Thyroid hormones