Thyroid disorders and breast cancer.

We have investigated the controversial association between diseases of the thyroid gland and breast carcinoma using methodology which allows positive exclusion of cases of breast disease from control groups and the detection of subclinical alterations in thyroid volume using high resolution ultrasonography, thus addressing the deficiencies of earlier studies. Whereas the prevalence of hyperthyroidism and hypothyroidism in patients with breast carcinoma and in healthy controls without clinical evidence of breast disease was similar, non-toxic goitre was more than twice as common in the breast carcinoma patients. Thyroid volumes were also significantly higher in breast carcinoma patients than in controls; using World Health Organisation criteria, 45.5% of breast carcinoma patients had thyroid enlargement compared with only 10.5% of controls. Finally, antithyroid peroxidase autoantibodies were twice as common in breast cancer patients than in controls. These findings provide clear evidence of a relationship between thyroid disease and breast carcinoma, although the mechanisms underlying this relationship require further study, future studies of breast cancer risk factors should therefore include assessment of thyroid function, antibody status and volume.