Endocrine Abstracts

Background: There are no definite recommendations on the optimal dosage of initiating adjuvant radioactive iodine (RAI) therapy for intermediate-risk differentiated thyroid cancer (DTC) patients in current relevant guideline. This study aimed to investigate the response of intermediate-risk DTC patients with a low (3.7GBq) or high RAI dose (5.55GBq).

Methods: Propensity score matching was performed to control for baseline characteristics. A total of 476 patients with intermediate-risk DTC were retrospectively reviewed. 238 patients received RAI of 3.7GBq (Group 1), and the other 238 patients received RAI of 5.55GBq (Group 2). Then patients were further divided into 4 subgroups: Subgroup 1: stimulated thyroglobulin (sTg) <10ng/ml, Subgroup 2: sTg ≥10ng/ml, Subgroup 3: N0+N1a, Subgroup 4: N1b. We compared the response to different RAI dose in subgroups. The univariate and multivariate logistic regression were conducted to screen out factors associated with excellent response (ER). Finally, the prognostic nomogram was used to explain ER rates as a useful tool in clinical practice.

Results: Before dividing the subgroups, The ER rate in Group 1 was higher than Group 2 (65.1% vs 47.1%, P<0.05). There was no significant difference of response to different RAI dose in subgroup 1. Group 1 has significantly higher incomplete response (IR) rates in Subgroup 2 and 4(71% vs 41.5%, 24.1% vs 10.9%, all P<0.05 respectively). However, in Subgroup 3, the ER rate in Group 1 and the IR rate in Group 2 were relatively higher. (69.2% vs 53.2%, 7.5% vs 15.6%, all P<0.05 respectively). By univariate and multivariate logistic regression analysis, N1b (OR:0.158, 95%CI: 0.034-0.736, P=0.019), sTg> 10ng/ml (OR:0.048, 95%CI: 0.022-0.104, P<0.001), and T2 (OR: 0.472, 95%CI: 0.228-0.981, P=0.044) were manifested to be independent risk factors for ER. The nomogram showed that sTg, N status and T status were the top 3 contributors to the ER.

Conclusions: Higher RAI dose should be considered for intermediate-risk DTC patients when sTg ≥10ng/ml or with N1b status.