Reflective analysis on the current I adjuvant therapy indications in intermediate- and high-risk differentiated thyroid cancer.

Purpose: Radioiodine (I) adjuvant therapy (RAT) is given to treat subclinical tumor of differentiated thyroid cancer (DTC) that may or may not actually be present after prior adequate treatment, yet the indications and benefits for RAT remain controversial. This multi-center study retrospectively evaluated the real targets and responses to RAT in intermediate- and high-risk patients, aiming to refine current "one-size-fits-all" guidelines.

Methods: Totally 599 intermediate- and high-risk DTC patients from three centers were enrolled. The post-operative disease status, instant purpose verification and 12-month response to RAT were assessed using thyroglobulin levels, imagings and post-therapy whole-body scan (Rx-WBS) during follow-ups.

Results: Totally 49.75% patients were assessed as post-operative disease status excellent response (ER)/indeterminate response (IDR), 37.56% patients were biochemical incomplete response (BIR) and 12.69% were structural incomplete response (SIR). Through instant purpose verification, 49.92%, 36.73%, and 13.36% patients were targeted at remnant thyroid, biochemical and structural/functional disease, respectively. 59.39%, 13.48%, 16.55%, and 10.58% patients were ER, IDR, BIR and SIR at 12-month final response, respectively. 95.64% patients with post-operative ER/IDR remained 12-month ER/IDR. 45.78% post-operative BIR converted to ER/IDR. Intermediaterisk, T1/T2 staging, non-thyroid capsule invasion, non-multifocal lesion, times of surgery, no abnormal finding on Rx-WBS were predictors for post-operative BIR transferred to 12-month ER/IDR (all P < 0.05).

Conclusion: Intermediate-risk patients with post-operative ER or IDR might be spared from aggressive RAT, and patients with post-operative BIR could be potential candidates for RAT at higher administered activities (>3.7 GBq, median 5.55 GBq, IQR 4.625 GBq-5.55 GBq), especially in those with less aggressive clinicopathological features who may even obtain ER/IDR at 12-month response.