Background: To investigate the role of primary hypothyroidism (HYPT) on breast carcinogenesis, the authors evaluated 1) the association between HYPT and a diagnosis of invasive breast carcinoma and 2) the clinicopathologic characteristics of breast carcinoma in patients with HYPT.
Methods: For this retrospective chart review study, 1136 women with primary breast carcinoma (PBC) were identified from the authors' departmental data base. These women (cases) were frequency-matched for age (+/- 5 years) and ethnicity with 1088 healthy participants (controls) who attended a breast carcinona screening clinic. Women with HYPT who were receiving thyroid-replacement therapy before they were diagnosed with breast carcinoma or before the screening visit were identified.
Results: The mean ages of cases and controls (51.6 years vs. 51.0 years, respectively; P = 0.30) and their menopausal status (65.4% premenopausal vs. 62% postmenopausal; P = 0.10) were comparable. Two hundred forty-two women in the case group (10.9%) with HYPT were identified. The prevalence of this condition was significantly greater the control group compared with the case group (14.9% vs. 7.0%, respectively; P < 0.001). PBC patients were 57% less likely to have HYPT compared with their healthy counterparts (odds ratio, 0.43l 95% confidence interval, 0.33-0.57). Seventy-eight white patients with PBC had HYPT and, compared with women who were euthyroid, they were older at the time of diagnosis (58.8 years vs. 51.1 years; P < 0.001), were more likely to have localized disease (95.0% vs. 85.9% clinical T1 or T2 disease, respectively; P = 0.025), and were more likely to have no pathologic lymph node involvement (62.8% vs. 54.4%; P = 0.15).
Conclusions: Primary HYPT was associated with a reduced risk for PBC and a more indolent invasive disease. These data suggest a possible biologic role for thyroid hormone in the etiology of breast carcinoma and indicate areas of research for the prevention and treatment of breast carcinoma.