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Hyperthyroidism increases breast cancer risk
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Women with hyperthyroidism have an increased risk for breast cancer, whereas there was a slightly decreased risk among women with hypothyroidism, according to study findings.
“In vitro experiments show that sex hormones such as estrogen play an important role in the proliferation of breast cancer cells,” Mette Søgaard, PhD, of the department of clinical epidemiology at Aarhus University in Denmark, said in a press release. “High levels of thyroid hormone levels can have estrogen-like effects, which may explain why hyperthyroidism is associated with higher risk of breast cancer.”
Mette Søgaard
Søgaard and colleagues evaluated all women in Denmark with a first-time hospital diagnosis of hypothyroidism (n = 61,873) or hyperthyroidism (n = 80,343) to determine the link between breast cancer risk and thyroid levels. Follow-up was a median 4.9 years for hypothyroidism and 7.4 years for hyperthyroidism.
An increased risk for breast cancer was found with hyperthyroidism (standardized incidence ratio [SIR] = 1.11; 95% CI, 1.07-1.16), whereas a slightly decreased risk was found with hypothyroidism (SIR = 0.94; 95% CI, 0.88-1). The increased risk for breast cancer associated with hyperthyroidism remained after 5 years of follow-up (SIR = 1.13; 95% CI, 1.08-1.19).
The risk for breast cancer associated with hyperthyroidism was not affected by censoring radioactive iodine treatment initiation (SIR = 1.08; 95% CI, 0.98-1.18) or excluding patients with Graves’ disease (SIR = 1.09; 95% CI, 1.02-1.16).
“We found an increased risk of breast cancer in women with hyperthyroidism and a slightly decreased risk in women with hypothyroidism suggesting an association between the thyroid function level and breast cancer risk,” the researchers wrote. – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.
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