Thyroid autoimmunity and breast cancer

PP Smyth, RM Dwyer, DF Smith, AD Hill, EW Mc Dermott, NJ O'Higgins

University College Dublin and St Vincent's University Hospital , Dublin, Ireland

An association between breast cancer and thyroid disorders has long been postulated. but despite extensive investigations, no common pathogenic factors have emerged. Aims. - To investigate the prevalence of thyroid disorders and indices of autoimmune thyroid disease in patients with breast cancer. -To evaluate a possible contribution of these indices to disease outcome. Methods. Serum TSH, thyroid peroxidase (TPO) and thyroglobulin (Tg) antibodies were measured by radioimmunoassay, thyroid volume by ultrasound and disease outcome in breast carcinoma assessed using Kaplan Meier survival curves. Results. Primary hypothyroidism, palpable nontoxic goiters and ultrasound measured thyroid enlargement were significantly greater than in age matched controls (p< 0.05) or (p< 0.001) for ultrasound measurement. TPO.Ab were present in 33.2% of breast cancer patients compared to 18.3% in controls (p< 0.01). The prevalence of TPO.Ab in patients with breast cancer increased with increasing serum TSH even when TSH values were within the normal range. Five year disease free survivals were 73.0 % in thyroid antibody positive patients compared to 55.0 % when antibodies were negative (RR = 1.84;p < 0.05). Multivariate analysis showed that the presence of thyroid antibodies was of similar orders of magnitude to established risk factors such as tumour size or nodal status. Conclusions. These findings in the largest group of breast cancer patients who to date have undergone detailed thyroid assessment, emphasize the importance of increasing awareness of the possible coincidence of the two disorders. They also demonstrate a coincidence of subclinical hypothyroidism associated with an underlying autoimmune thyroid disease which may be a positive prognostic factor in breast cancer.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Autoimmunity.