Thyroid disease and breast cancer.

A review of the literature on the relationship between thyroid disorders and breast cancer does not provide conclusive evidence for the establishment of a causal relationship as breast cancer has been associated with hypothyroidism, hyperthyroidism and nontoxic goiter. Most reports on the association of thyroid enlargement and breast cancer have emanated from areas of endemic iodine deficiency and these reports have relied on neck palpation. The contribution of the present study is in the application of the highly sensitive technique of diagnostic ultrasound to the investigation of subtle changes in thyroid volume and anatomy in patients with breast cancer. The mean thyroid volume of 20.4 +/- 1.0 ml in 184 breast cancer patients was significantly greater than that of 12.9 +/- 1.2 ml in age-matched controls (p < 0.01). Also the number of individual patients with breast cancer having enlarged thyroid glands (73/184; 39.7%) was significantly greater than the corresponding number (13/150; 8.6%) in the control group (p < 0.001). There was a direct correlation between thyroid enlargement and breast tumour staging. Both mean thyroid volume and % of enlarged thyroids were identical in groups of patients scanned after (Retrospective Group) and before (Prospective Group) various therapies for breast cancer, thus excluding therapeutic intervention as a cause for thyroid enlargement. The results indicate a direct relationship between the two disorders perhaps involving a common growth stimulus and emphasise the importance of raising the consciousness of the coincidence of both disorders.