Analysis of the clinical factors affecting excellent response of Iodine-131 treatment for pulmonary metastases from differentiated thyroid cancer.

[BACKGROUND] Iodiene-131 (I) treatment is the primary therapeutic approach for imaging I-avid pulmonary metastases. The response to radioiodine (RAI) treatment is an important prognostic factor in patients with pulmonary metastases from differentiated thyroid cancer (DTC). Patients who achieve an excellent response (ER) to I treatment show significantly reduced disease-related mortality. This study aimed to retrospectively analyse the clinical data and therapeutic effects of I treatment in patients with DTC and pulmonary metastases and to screen out the clinical factors affecting ER.

[MATERIALS AND METHODS] The study included a total of 75 patients with exclusively Iodine-131 avid (I-avid) pulmonary metastases who underwent I treatment. Relevant clinical data for these patients were collected. Following treatment, the status of DTC metastatic lesions was categorized as follows: excellent response (ER), biochemical incomplete response (BIR), structural incomplete response (SIR), or indeterminate response (IDR). Gender, age at diagnosis, pathological type, stages (TNM), stimulated thyroglobulin (sTg) value before initial I treatment, metastatic nodule size, and type of post-treatment whole body scan (Rx-WBS) were recorded. Mono-factor analysis and binary logistic regression analyses were used to identify the factors that might affect the ER in DTC pulmonary metastases. The receiver operating characteristic (ROC) curve of the sTg value was used to predict the ER of I treatment.

[RESULTS] All 75 patients with exclusively I-avid pulmonary metastases received I treatment and underwent follow-up. Out of the 75 patients, 26 achieved ER, resulting in an excellent response rate of 34.7 % (26/75). Among them, 25 (25/26, 96.2 %) achieved an ER after undergoing two rounds of I treatment. Binary logistic regression analysis showed that the factors influencing DTC pulmonary metastases excellent response were lower sTg levels [odds ratio () = 0.998,  < 0.001], micronodular metastases ( = 0.349,  = 0.001) and focal distribution on Rx-WBS imaging ( = 0.113,  = 0.001). The area under the ROC curve for sTg value predicting ER was 0.876, and the cut-off value was 26.84 ng/mL, with a sensitivity and specificity of 87.9 % and 80.3 %, respectively.

[CONCLUSIONS] I treatment is effective for I-avid pulmonary metastases of DTC. Some patients who underwent I treatment achieved ER. Most patients with ER were obtained after two rounds of I treatments. Patients with sTg values before initial I treatment lower than 26.84 ng/mL, micronodular metastases, and focal distribution on Rx-WBS imaging were more likely to achieve ER.