Long-term outcome of low and intermediate risk differentiated thyroid carcinoma patients who had initial R0 dissection and received no radioiodine therapy

Aim: Radioactive iodine (RAI) therapy is not routinely recommended in low risk differentiated thyroid cancer (DTC) patients according to American Thyroid Association (ATA) 2015 guidelines, however, that is a weak recommendation and based on low quality evidence. In intermediate risk DTC patients empiric RAI therapy is routinely recommended, even in the absence of structural disease, just based on the risk. These recommendations are often challenged due to non-uniform criteria of defining low and intermediate risk of recurrence. We have been following a large cohort of low and intermediate risk DTC patients who had initial R0 dissection confirmed by 131I- whole body scan (WBS) and not given any RAI and being followed meticulously over long period of time. This retrospective cohort study intends to share the recurrence-free survival of such patients.

Methods: All DTC patients who had total thyroidectomy + neck nodal dissection, and freshly risk-stratified as per ATA 2015 guideline (many intermediate risk patients down staged as low-risk only); moreover all had 131I-WBS to document R0 dissection. The cohort consists of total 844 DTC patients with no RAI therapy but on appropriate level of TSH suppression, being followed with clinical examination, Tg, anti-Tg, thyroid hormone profile and neck ultrasound examinations annually. The study included those patients who had at least 12 months of follow up at the time of analysis.

Results: 698 patients had follow up of >12 months (females were 539). The follow up period ranged from 12 to 286 months with median of 69 months. Overall, 25/698(3.6%) patients recurred; 14/529 (2.6%) in low risk and 11/169 (6.4%) in intermediate patients had recurrence. The time of recurrence ranged from 12 to 190 months. The sites of recurrence - 16/25 (64%) had recurrence in neck nodes, and remaining 9 had recurrence in distant sites- lung 5 and bones 4. All 16 nodal recurrence patients had neck dissection except one, who refused neck dissection. All 9 distant metastasis patients received high dose of RAI therapy. Significant association has been found between recurrence in low risk patients with post-operative stimulated Tg level. On ROC analysis, stimulated-Tg more than 8 predicted recurrence in low-risk patients with AUC of 0.722. Interestingly, no significant association has been found between recurrence in intermediate risk DTC patients and immediate post-op stimulated-Tg values.

Conclusions: If one could achieve initial R0 dissection in low and intermediate risk DTC patients, the requirement of remnant ablation/adjuvant RAI therapy becomes superfluous, in view of very low recurrence rate (overall 3.6%, 2.6% in low and 6.4% in intermediate risk group) with median follow up of 69 months. However, current criteria for risk stratification to call low and intermediate risk DTC needs further refinement.