Consider or not consider: the unsolved question on the use of radioactive iodine for differentiated thyroid cancer with low to intermediate risk of recurrence

Abstract

Background: Surgery stands as the cornerstone treatment for differentiated thyroid cancer (DTC). After surgery, radioactive iodine (RAI) administration is primarily recommended for high-risk patients and commonly employed to address residual disease or mitigate the risk of recurrence. However, the optimal application of RAI in cases categorized as low to intermediate risk is still uncertain. This study aims to assess the indication of post-surgical RAI treatment specifically in patients diagnosed with DTC falling within the low to intermediate risk category for recurrent disease.

Methods: retrospective analysis of consecutive patients with DTC falling within the low to intermediate risk category for recurrence and diagnosed between 2009-2015. Patients were categorized into either treated or untreated with RAI. Treatment effect was assessed by the inverse-probability weighted regression adjustment (IPWRA), by balancing the distribution of factors influencing outcome and treatment assignment.

Results: after surgery, 328 patients (69.9%) were treated with RAI while 141 (30.1%) were left untreated. Across the entire cohort, 44 individuals (9.4%) displayed biochemical or structural disease after a median time of 17.5 months following diagnosis. Recurrent disease was more prevalent in patients who underwent RAI treatment compared to those untreated (12.5% vs 2.1%, respectively, p < 0.001). Factors independently associated with recurrent disease, identified through multivariate logistic regression analysis, included lymph node metastases (pN1) (OR = 4.07; 95% CI 1.84-8.97), male sex (OR = 2.71; 95% CI 1.31-5.59), tumor size (OR = 1.03; 95% CI 1.00-1.06), and microscopic extrathyroidal extension (OR = 2.36; 95% CI 1.15-4.81). IPWRA analysis revealed that the occurrence of recurrent disease was 9.6% (95% CI = 6.3-12.9) in RAI-treated patients and 15.9% (95% CI = 11.1-20.71) in untreated patients (p = 0.021). As a consequence, if all patients underwent RAI treatment, the estimated risk of recurrence would be reduced by 42% (RR = 0.58; 95% CI = 0.35-0.91, p = 0.018). The greatest benefit was observed in patients with 2 intermediate risk factors.

Conclusions: These results suggest that treatment with RAI in low to intermediate DTC can reduce the risk of recurrence in selected patients. However, definitive answers regarding whether to consider RAI therapy for this category of patients can only be attained through prospective clinical trials. Up to date these results recommend a meticulous assessment of tumor characteristics at diagnosis to guide the decision regarding RAI administration.

Keywords: differentiated thyroid carcinoma; predictive factors; radioactive iodine; recurrent disease; treatment effect.