Abstract
BackgroundThe issue of a potential association between thyroid conditions/hormones and breast cancer has been studied extensively during the last decades but the results have been inconclusive and almost no studies have investigated breast cancer aggressiveness. We have previously found a positive association between prospectively measured levels of triiodothyronine (T3) and breast cancer incidence as well as breast cancer mortality. We now investigated prediagnostic T3 levels in relation to specific prognostic factors in breast cancer.MethodsThe Malmö Preventive Project is a population-based prospective cohort including 2185 women in whom T3 levels were measured at baseline. That is, total T3 levels were measured before a potential diagnosis of breast cancer. Mean follow-up was 23.3 years and 149 women in the study population were diagnosed with invasive breast cancer. Tumours were classified according to selected prognostic factors of breast cancer; i.e. grade, tumour size, lymph node metastasis, and hormonal receptor status. T3 was handled both as tertiles and as a continuous variable. A Cox’s proportional hazards analysis yielded hazard ratios with 95% confidence intervals. All analyses were also restricted to postmenopausal women.ResultsOverall there was a statistically significant association between T3 and “all” breast cancers. The adjusted Hazard Ratio (HR) in the third tertile, as compared to the first, was (1.61:1.07-2.43). There was a statistically significant positive association between the third T3 tertile and large tumours, i.e. > 20 mm, (3.17:1.20-8.36) and the occurrence of lymph node metastases, (4.53:1.60-12.83). Other prognostic factors positively associated with T3 were negative oestrogen receptor (ER) status, (3.52:1.32-9.41) and negative progesterone receptor (PGR) status, (3.52:1.42-8.75). The analyses of T3 as a continuous variable and analysis restricted to postmenopausal women, confirmed the results but also showed an association with smaller tumours and in postmenopausal women a contemporary association with negative lymph nodes.ConclusionsThis prospective study of serum T3 levels in relation to breast cancer aggressiveness is the first of its kind. We found statistically significant positive associations between higher prediagnostic T3 levels and larger tumours, occurrence of lymph node metastases, and negative ER and PGR status.
Highlights
The issue of a potential association between thyroid conditions/hormones and breast cancer has been studied extensively during the last decades but the results have been inconclusive and almost no studies have investigated breast cancer aggressiveness
The aim of the present study was to investigate the association between prediagnostic T3 levels and prognostic factors related to breast cancer aggressiveness; i.e. tumour size, grade, lymph node metastases, and hormonal receptor status.This was studied in a prospective cohort of 2185 women, out of whom 149 were diagnosed with invasive breast cancer during a follow-up of at least 18 years
All breast tumours The third T3 tertile had a statistically significant association with “all” breast cancers in the analysis adjusted for age and oral contraceptives (OC) (Table 3)
Summary
The issue of a potential association between thyroid conditions/hormones and breast cancer has been studied extensively during the last decades but the results have been inconclusive and almost no studies have investigated breast cancer aggressiveness. The issue of a potential association between thyroid conditions/ hormones and breast cancer risk has been studied extensively during the last decades but the results have so far been inconclusive [1,2,3]. Interpretation of previous studies is difficult as almost all have been cross-sectional This is a major problem when measuring thyroid hormones in breast cancer patients as the disease per se, as well as its treatment, may affect hormonal levels. One study has shown that thyroid autoimmunity in relation to breast cancer aggressiveness is associated with a lower frequency of distant metastasis [6]. An early cross-sectional study by Lemaire et al showed no relation between thyroid function and TNM stage of breast cancer [8]
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