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 (131)I therapy and 1,834 controls (thyroid cancer without (131)I therapy) selected by 1:1 matching on a propensity score were enrolled. The cumulative (131)I dose in each patient was calculated. A Cox proportional hazards model was applied to estimate the effect of radiation from the (131)I 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 (131)I 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: (131)I 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 (131)I treatment and KCS development.