Breast Cancer Patients May Have Subtle Thyroid Dysfunction

Zosia Chustecka

October 19, 2007

October 19, 2007 -- Breast cancer patients may have subtle hypothyroidism, even in the absence of overt or subclinical hypothyroidism, a new study suggests. The results were reported at the American Thyroid Association 78th Annual Meeting, in New York, by Peter Smyth, PhD, and colleagues, from University College, Dublin, Ireland.

The study compared 710 consecutive patients with postmenopausal breast cancer who were asymptomatic for thyroid disease with 179 postmenopausal controls. The results show that the breast cancer patients had significantly higher levels of antithyroid autoantibodies (TPOAb) and higher levels of serum thyroid stimulating hormone (TSH).

The autoantibodies levels were undetectable in 51.8% of breast cancer patients compared with 82.1% of controls ( P < .001), and this relationship continued for detectable values (24.5% in patients vs 3.9% in controls; P < .001) and for elevated values (22.9% in patients vs 14.0% in controls; P < .01).

Investigation of serum TSH levels in these groups showed not only that there was an association between elevated levels of antithyroid autoantibodies and serum TSH but also that that this association applied to those patients with breast cancer who had detectable levels, Dr. Smyth told the meeting. In the case of elevated levels of antithyroid autoantibodies, serum TSH greater than 4.0 mU/L was found in 61.5% of breast cancer patients compared with 20% of controls ( P < .001), while the corresponding figures for detectable levels were 24.3% for patients and 0 for controls ( P < .001).

Asked by Medscape Oncology to comment on this finding, Jayne Franklyn, MD, PhD, from Queen Elizabeth Hospital, in Birmingham, United Kingdom, who was not involved with the study, said: "There has been a suspicion for many years that there is an association between hypothyroidism and breast cancer, but the evidence has been conflicting. What this study shows is that antithyroid antibodies are more likely to be present and more likely to be elevated in breast cancer patients than controls, and these autoantibodies are associated with the very early stages of hypothyroidism." It suggests that there may a link between an autoimmune disease such as antibody-positive hypothyroidism and the risk of developing breast cancer, so this work advances the understanding of science, Dr. Franklyn said. However, there are no immediate practical or clinical implications from this work, such as, for example, investigating thyroid function in breast cancer patients, she added.

78th Annual Meeting of the American Thyroid Association: Abstract 157. Presented October 5, 2007.

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