131I treatment for thyroid cancer and the risk of developing salivary and lacrimal gland dysfunction and a second primary malignancy: a nationwide population-based cohort study

Objective The aim of this study was to determine the prevalence of salivary and lacrimal gland dysfunction and a second primary malignancy in patients from Taiwan with thyroid cancer after radioiodine therapy. Methods This nationwide population-based cohort study was based on data obtained from the Taiwan National Health Insurance Database from 2000 to 2011. A total of 1,834 thyroid cancer patients treated with I-131 therapy and 1,834 controls (thyroid cancer without I-131 therapy) selected by 1:1 matching on a propensity score were enrolled. The cumulative I-131 dose in each patient was calculated. A Cox proportional hazards model was applied to estimate the effect of radiation from the I-131 therapy on the risk of salivary and lacrimal gland impairment as well as second primary malignancies in terms of hazard ratios (HRs) and 95 % confidence intervals (CIs). Results In patients treated with I-131 therapy and in controls, the incidence rates of salivary gland dysfunction were 6.76 and 1.01 per 10,000 person-years, respectively (HR 6.81, 95 % CI 0.74 - 55.3), the incidence rates of keratoconjunctivitis sicca (KCS) were 13.6 and 16.3 per 10,000 person-years, respectively (HR 0.84, 95 % CI 0.41 - 1.73), and the incidence rates of second primary malignancy were 76.7 and 62.4 per 10,000 person-years, respectively (HR 1.23, 95 % CI 0.88 - 1.72). The risk of salivary secretion impairment significantly increased with increasing administered doses (HR 14.3, 95 % CI 1.73 - 119.0). However, there was no increase in the incidence of KCS or secondary cancer in patients treated with higher doses. Conclusion I-131 therapy insignificantly increased the risk of salivary gland dysfunction and second primary malignancy. In patients with higher cumulative doses, an increase in the incidence of salivary gland dysfunction was observed. By contrast, we did not find an association between I-131 treatment and KCS development.