The effects of stimulated thyroglobulin/ thyroid-stimulating hormone ratio and N1b status on the efficacy of the first I-131 treatment in patients with differentiated thyroid cancer

Background: Thyroglobulin (Tg) level is one of the well-known factors affecting the outcome of radioactive iodine treatment in differentiated thyroid cancer, though this tumor marker is affected by the thyroid-stimulating hormone (TSH) level. To negate this influence, there is an effort to use the stimulated thyroglobulin/ thyroid-stimulating hormone (sTg/TSH) ratio instead of stimulated thyroglobulin (sTg) level alone. N1b cervical lymph node metastasis is also another factor mentioned in literature. This study aims to demonstrate the significance of these two factors whether they affect the treatment outcome in differentiated thyroid cancer patients who received the first radioactive iodine treatment. Methods: This was a retrospective analytical observational study. The population were patients with differentiated thyroid cancer with an age of 18 years and above who received the first radioactive iodine treatment at our center from 1 January 2020–31 December 2023. The total population was 227 patients. Logistic regression analysis was done to determine the significant factors affecting the outcome of the first radioactive iodine treatment. Results: In 227 patients, the median value for sTg and sTg/TSH ratio were 9.4 ng/mL and 0.2, respectively. Multiple logistic regression found that sTg/TSH ratio and N1b status were not independent risk factors for non-excellent response after radioactive iodine treatment. The independent risk factors were male sex, intermediate and high risk of recurrence, stage II and sTg of more than or equal to 9.4 ng/mL. Receiver operating characteristic (ROC) analysis showed that sTg and sTg/TSH ratio had rather similar performance in differentiating between excellent and non-excellent response groups. Conclusion: sTg/TSH ratio and N1b cervical lymph node metastasis were not significant independent factors for non-excellent response after the first radioactive iodine treatment, which was possibly due to multicollinearity and small sample size. Independent risk factors for non-excellent response of the first radioiodine treatment were male sex, intermediate and high risk of recurrence, stage II and sTg of more than or equal to 9.4 ng/mL.