Young Women Are at High Risk for Comorbid Thyroid Disease and Breast Cancer

Approximately 50% of the population has at least one thyroid nodule by age 60, although only 5% of those nodules are malignant.

Patients who are diagnosed with other cancers have an increased risk of a second primary thyroid cancer, while those diagnosed with differentiated thyroid cancer are at increased risk of a second primary malignancy. Researchers are interested in both populations because they may explain genetic and environmental factors that put patients at risk and contribute to causality.

Noting studies that have evaluated the association between breast cancer (BC) and benign or malignant thyroid diseases reported conflicting results, researchers from the University of Rome compared 3,921 female patients affected by both benign and malignant thyroid diseases (TD) to the general population in order to establish BC prevalence.

For their study published in the March 2014 issue of Breast Cancer Research and Treatment, the authors identified 3 diagnostic categories: 1,149 patients with non-nodular TD, 2,350 patients with nodular TD, and 422 patients affected by differentiated thyroid cancers. They also recorded the absence (n=2,344) or presence (n=1,453) of anti-thyroglobulin (TgAb) and/or anti-thyroperoxidase (TPOAb) or anti-TSH receptor auto-antibodies (n=124). Using age-matched analysis, they established BC prevalence.

According to the authors, TD patients were 3.33 times more likely to develop BC. While those aged younger than 44 had a significantly elevated risk of BC with an odds ratio of 15.24, that risk decreased with age. Those who lacked thyroid autoantibodies were more likely to develop BC than those with TgAb and/or TPOAb, which indicated thyroid autoantibodies may be protective for BC.

Nevertheless, the TD-BC association remains unclear. Some hypotheses include a direct and indirect action of thyroid hormones (TH) on BC cells, given that some BC patients experience deregulated expression of TH receptors, and TH can bind and activate the estrogen receptor in BC cells. Research has also determined that TH can increase estrogen receptor expression. BC patients have also been shown to have higher free T3 levels than control subjects.

Though the findings suggest clinicians should have a high index of suspicion for comorbid breast and thyroid disease, the authors noted additional studies are needed to confirm this relationship.