Background

Differentiated thyroid cancer (DTC) is the most common endocrine malignancy in the United States. Treatment for DTC typically involves surgery followed by radioactive iodine (RAI) for remnant ablation to reduce the risk of recurrence. RAI may be associated with complications, including salivary and lacrimal dysfunction, and secondary malignancies. The 2015 American Thyroid Association (ATA) guidelines for DTC proposed a three-tiered risk stratification system consisting of low, intermediate and high risk for predicting disease recurrence and guiding post-surgical management. Recommendations for RAI use in low- and high-risk cancers are widely accepted, but those for intermediate-risk cases remain controversial due to conflicting results from the available data.

Study Design

The aim of this study is to determine if RAI therapy after total thyroidectomy affects the rates of structural recurrence in patients with differentiated thyroid cancer at intermediate and high risk of recurrent disease. This project will be a retrospective cohort study of adult patients with intermediate- or high-risk DTC who were or were not treated with adjuvant radioactive iodine therapy after thyroidectomy. Data will be collected from adult patients within the UCLA Health and Los Angeles County and University of Southern California health systems between January 2010 and December 2018, with follow-up evaluated to present.

Interim Data Analysis

We completed an interim analysis of 100 eligible UCLA patients. Our demographics data indicates an interquartile age range of 37 to 60, which will capture key groups of younger and older patients.        We have a strong median time of follow up of nearly 3 years. We have divided our interim cohort into 4 study groups: intermediate risk with RAI ablation (68 patients), intermediate risk without RAI (14 patients), high risk with RAI ablation (17 patients) and high risk without RAI (1 patient). Our initial results show the rate of structural recurrence is somewhat reduced in patients with RAI ablation, 11% compared to 20% without RAI ablation.

Statistical Methods & Next Steps

Descriptive statistics will be calculated for the overall cohort as well as the RAI+ and RAI- groups separately. Student’s t-test and the Chi-square test will be used to compare patient characteristics between the two groups. Cox proportional hazards regression will compare rates of recurrence-free survival between patients who receive and do not receive RAI. Our anticipated complete cohort of 600 patients will be sufficient to address our primary outcome measure in a clinically meaningful way.