Hypothyroidism, HT exert opposite risks for postmenopausal breast cancer
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In a large prospective cohort of postmenopausal women, those who had ever had hypothyroidism — whether treated with levothyroxine or not — were less likely to develop breast cancer than those without hypothyroidism, and the relationship was more pronounced among those who did not also use menopausal hormone therapy, according to findings published in Thyroid.
“About one in eight women may have a thyroid disorder in their lifetime, and breast cancer shares similar lifetime prevalence. Mammary and thyroid glands share some physiological similarities, and several in vitro studies have shown that high levels of thyroid hormones seem to possess estrogen-like effects, which promote breast cancer proliferation and angiogenesis,” Chien-Hsiang Weng, MD, MPH, assistant professor in the department of family medicine at Brown University Warren Alpert Medical School in Providence, Rhode Island, told Healio. “Menopausal hormone therapy and the risk of breast cancer in postmenopausal women have been investigated for more than a decade. Our study is the first to examine the role of thyroid disease, [menopausal hormone therapy] and breast cancer risk.”
Weng and colleagues compared data from 111,740 postmenopausal women who had never had a thyroid disorder (mean age, 62.8 years), 19,735 postmenopausal women who had experienced hypothyroidism (mean age, 63.9 years), 1,695 postmenopausal women who had experienced hyperthyroidism (mean age, 63.4 years) and 952 postmenopausal women who had experienced both hypothyroidism and hyperthyroidism (mean age, 63.1 years). Thyroid disorder history was self-reported. From baseline (1993-1998) to 2017, the researchers also used biannual self-reports and medical records to determine diagnoses of breast cancer.
Researchers observed a reduction in breast cancer risk for those who had experienced hypothyroidism vs. those who had not (HR = 0.91; 95% CI, 0.86-0.97).
“Although several hypotheses have been proposed to explain the association between hypothyroidism and breast cancer, no consensus has been reached,” the researchers wrote. “It has been suggested that hypothyroidism leads to hypersensitization of mammary glandular epithelium to estrogen and prolactin secondary to abnormally low circulating thyroid hormone. It has also been hypothesized that there is a genetic predisposition for both hypothyroidism and breast cancer.”
There was also a reduction in breast cancer risk for those treated with levothyroxine vs. those not treated with levothyroxine (HR = 0.89; 95% CI, 0.82-0.96).
“It is important to discuss the importance of receiving thyroid replacement therapy, specifically with levothyroxine, for menopausal women with a history of hypothyroidism since it may be associated with a lower risk of breast cancer, and may also discuss about the diminished protective effect with menopausal hormone therapy for any duration in this particular population,” Weng said. “Though, further in vitro and clinical studies are needed to elucidate the relevant mechanisms and associations.”
Among women who were treated for hypothyroidism, breast cancer risk was lower for those who did not use menopausal hormone therapy vs. those who did (HR = 0.8; 95% CI, 0.69-0.93) .
“Hypothyroidism was associated with a lower risk of breast cancer development, and the relationship was strongest among those who received thyroid hormone replacement and had never used menopausal HT,” the researchers wrote. – by Phil Neuffer
For more information:
Chien-Hsiang Weng, MD, MPH, can be reached at chien-hsiang_weng@brown.edu; Twitter: @brycechipmunk.
Disclosures: The authors report no relevant financial disclosures.
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