Analysis of the impact of Graves' disease on the efficacy of initial radioactive iodine therapy in patients with differentiated thyroid cancer.

This study aimed to assess the impact of Graves' disease (GD) on the clinicopathological characteristics and prognosis of patients with differentiated thyroid cancer (DTC) undergoing initial radioactive iodine (RAI) therapy, as well as to identify factors influencing RAI therapy outcomes. A retrospective analysis was conducted on 959 DTC patients who received initial RAI therapy at the Department of Nuclear Medicine, First Affiliated Hospital of Nanchang University, between January 2021 and December 2023. Patients were divided into two groups based on a history of GD: the GD group (n = 60) and the non-GD group (n = 899). Data on demographics, laboratory tests, clinicopathological features, and RAI-related parameters were collected. Univariate analysis was performed to identify variables associated with treatment response, followed by multivariate logistic regression to determine independent predictors of outcomes after initial RAI therapy. The distribution of treatment responses across the four categories was as follows: in the GD group, excellent response (ER) occurred in 71.67%, indeterminate response (IDR) in 16.67%, biochemical incomplete response (BIR) in 6.67%, and structural incomplete response (SIR) in 5.00%; in the non-GD group, the respective rates were 39.60% (ER), 29.37% (IDR), 17.80% (BIR), and 13.24% (SIR). Statistically significant differences were observed in dichotomous outcomes - ER versus non-excellent response (N-ER), and ideal/acceptable response versus incomplete response - between the two groups (both P < 0.01). Multivariate analysis identified several independent factors associated with favorable RAI outcomes, including younger age, GD (P < 0.001; OR = 0.16; 95% CI: 0.07-0.35), shorter interval between surgery and I administration, fewer metastatic lymph nodes, negative pre-ablation thyroglobulin antibody (pa-TgAb), lower pre-treatment stimulated thyroglobulin (sTg) levels, and higher I dose (all P < 0.05). In contrast, Hashimoto's thyroiditis (HT), maximum diameter of metastatic lymph nodes, body mass index (BMI), tumor multifocality, maximum tumor diameter, tumor location, and ATA recurrence risk stratification were not significantly associated with treatment response (all P > 0.05). Compared to non-GD DTC patients, those with GD exhibited more favorable pathological features and significantly better short-term prognosis following initial RAI therapy, with an 84% reduced likelihood of N-ER. Key predictors of favorable RAI response included GD status, younger age, shorter surgery-to-RAI interval, lower metastatic lymph node burden, pa-TgAb negativity, lower sTg levels, and higher I dose. HT, metastatic lymph node size, BMI, tumor multifocality, tumor size, and tumor location did not significantly influence treatment outcomes.