The majority of patients (61%) were male, with an average age of 36 years. Overall, 80% of patients had classical papillary thyroid cancer (PTC), while the rest had the follicular variant of PTC. Patients with pre-existing high anti-TPO antibody levels measured in banked sera collected 7 to 10 years prior to the thyroid cancer diagnosis had nearly double the odds of developing thyroid cancer. This association was 2.5 increased in females as compared to 1.6 times increased in males. In addition, the thyroid cancer risk increased as the serum anti-TPO antibody levels increased. Smoking did not affect the association between thyroid autoimmunity and thyroid cancer in this population.
Additional analysis showed that a pre-existing diagnosis of autoimmune thyroid disease accounted for 35% of the increased likelihood of these patients to be diagnosed with thyroid cancer. However, these patients had more favorable cancer features (e.g., smaller cancer size and less often spread into the neck lymph nodes), indicating a less aggressive cancer and/or diagnosis at earlier stages in thyroid cancer patients with known thyroid autoimmunity because of increased screening in this group.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study showed that long-standing autoimmune thyroid disease (up to 10 years prior to thyroid cancer diagnosis) is associated with papillary thyroid cancer. Patients with higher thyroid autoantibody titers had a higher risk of developing papillary thyroid cancer. Patients with known thyroid autoimmune disease were diagnosed with thyroid cancer at earlier stages, because of close monitoring of these patients.
— Alina Gavrila, MD, MMSC