BACKGROUND:

This study examined the risk of cancer in patients with Hashimoto's thyroiditis (HT).

METHODS:

The Taiwanese National Health Insurance Research Database (NHIRD) was used to identify 1521 newly diagnosed HT patients from 1998-2010, and 6084 frequency-matched non-HT patients. The risk of developing cancer for HT patients was measured using the Cox proportional hazard model.

RESULTS:

The incidence of developing cancer in the HT cohort was 5.07 per 1000 person-years, which was 1.68-fold higher than that in the comparison cohort (P<0.001). Compared with patients aged 20-34 years, patients in older age groups had a higher risk of developing cancer (35-55 years: hazard ratio (HR)=5.96; >55 years: HR=9.66). After adjusting for sex, age, and comorbidities, the HT cohort had HRs of 4.76 and 11.8 for developing colorectal cancer and thyroid cancer, respectively, compared with non-HT cohort. Furthermore, the HT cohort to non-HT cohort incidence rate ratio (IRR) of thyroid cancer was higher in the first 3 years (48.4, 95% confidence interval (CI)=35.0-66.3), with an adjusted HR of 49.4 (95% CI=6.39-382.4).

CONCLUSION:

Hashimoto's thyroiditis patients have a higher risk of thyroid cancer and colorectal cancer. The thyroid cancer prevention effort should start soon after HT is diagnosed, while being cautious of colorectal cancer increases with time.