Clinical Outcomes and Implications of Radioactive Iodine Therapy on Cancer-specific Survival in WHO Classification of FTC.

[BACKGROUND] The clinical outcomes and implications of radioactive iodine therapy (RAIT) on cancer-specific survival (CSS) in World Health Organization classification of follicular thyroid carcinoma (FTC) are not well established.

[MATERIAL AND METHODS] The data of eligible patients with minimally invasive FTC (mi-FTC), encapsulated angioinvasive FTC (ea-FTC), or widely invasive FTC (wi-FTC) between 2000 and 2020 were extracted from the Surveillance, Epidemiology, and End Results database. CSS, the primary outcome, was compared among the 3 subtypes of patients with FTC before and after adjusting for differences using propensity score matching (PSM). The patients with FTC in different subtypes were then divided into 2 groups: the RAIT group and the no-RAIT group. Cox proportional hazards regression analyses were applied to discover the relationships of factors associated with CSS in the each PSM cohort.

[RESULTS] A total of 2433 patients with mi-FTC, 216 patients with ea-FTC, and 554 patients with wi-FTC were enrolled in the original cohorts, respectively. Patients with mi-FTC or ea-FTC had similar CSS (P = .805), which was better than that of patients with wi-FTC (P < .001; P = .021). Cox proportional hazards regression analysis revealed that RAIT was not associated with improved CSS in either the mi-FTC PSM cohort (hazard ratio [HR], 1.21; 95% CI, .46-3.18; P = .705) or the wi-FTC PSM cohort (HR, 0.56; 95% CI, .35-1.08; P = .086). However, subgroup analysis demonstrated that patients with wi-FTC and N1 stage (HR, 0.44; 95% CI, .20-.99; P = .018) or M1 stage (HR, 0.25; 95% CI, .11-.53; P < .001) could gain CSS advantage from RAIT.

[CONCLUSION] The RAIT can provide a CSS advantage for patients with wi-FTC who with N1-stage or M1-stage disease.