Thyroid hormones and breast cancer-prospective studies on incidence, mortality and prognostic factors

Abstract: Thyroid hormones and breast cancer-prospective studies on incidence, mortality and prognostic factors The aim of this thesis was to investigate in a prospective design, thyroid hormones in relation to breast cancer risk, mortality and prognostic factors. The association between total triiodothyronine (T3) levels and breast cancer risk was studied in 2185 women with146 incident breast cancer cases. The association of free T3 and free thyroxin (T4) levels in relation to breast cancer risk was studied in 676 breastcancer cases and 680 controls. It was found that: Total T3 levels in postmenopausal women are positively associated with the risk of developing breast cancer in a dose-response manner. Free T4 levels also appear to be positively associated with a higher risk of breast cancer. The association between thyrotropin (TSH) levels and breast cancer risk was studied in 2696 women with173 incident breast cancer cases. The association between TSH and thyroid peroxidase antibodies (TPO-Ab) and breast cancer risk was studied in 676 breastcancer cases and 680 controls. It was found that: Women with a high level of TPO-Ab have a slightly lower risk of breast cancer, whereas TSH levels are not associated with breast cancer risk. The association between total T3 and prognostic factors in breast cancer and breast cancer mortality was studied in 2185 women where 26 died from breast cancer. It was found that: Total T3 levels are positively associated with breast cancer-specific mortality, which is not related to a general effect on all-cause mortality. Total T3 levels have a positive association to negative prognostic factors in breast cancer such as the occurrence of lymph node metastases, and negative oestrogen and progesterone receptor status. It is concluded that thyroid hormone levels are positively related to breast cancer risk and prognosis.