SAT525 Long-Term Outcomes in Stage I Thyroid Cancer Without Radioiodine Remnant Ablation

Abstract

Abstract Disclosure: F. Mubeen: None. M. Zahid: None. T.D. Cubb: None. J. Shakil: None. J. Xu: None. R.J. Robbins: None. Introduction: Although differentiated thyroid cancer (DTC) has low mortality, the risk of recurrence after thyroidectomy is not negligible. In the past radioiodine was routinely given to almost all patients following surgery to achieve radioiodine remnant ablation (RRA). We hypothesized, omission of RRA in Stage I (American Joint Committee on Cancer [AJCC] 8th edition) DTC survivors would not be inferior to RRA. Methods: We did a retrospective analysis of thyroid cancer survivors at a single academic medical center from 2000 to 2021. Patients with under six months follow-up, medullary or undifferentiated thyroid cancer, Stage II, III, or IV cancer or those who did not have total thyroidectomy were excluded. 208 Stage I (AJCC) DTC patients met inclusion criteria and were divided into two groups: those who had RRA (RRA+; n=121) and those who did not (RRA-; n=87). Primary outcome assessed was persistent/recurrent disease (P/RD). Results: P/RD was seen in 6.25% of patients at closing the study. RRA+ patients were significantly younger (42.88±13.02 vs. 46.84±13.98, p = 0.037), had a longer follow-up duration (111.23 (IQR: 51.80-161.27) vs. 78.87 (53.13-111.93) months, p=0.003), but there was no difference in sex distribution (p = 1.0). The RRA+ group had significantly higher multicentric tumors (66 (54.55%) vs. 32 (36.78%), p<0.001), larger tumors ( T3 and T4 , 25(20.67%) vs 3 (3.45%), p<0.001) and spread to loco-regional LN (48 (39.67%) vs. 8 (9.20%), p=0.001). P/RD was present in 13 survivors with RRA+ group having a slightly, but not significantly higher incidence of P/RD (11 (9%) in RRA+ vs. 2 (2.3%) in RRA-, P=0.078). In the 98 patients with presence of multicentricity, P/RD was seen in 1 (3.1%) of 32 RRA- and 8 (12.1%) of 66 RRA+ patients. The percentage of RRA+ patients who had P/RD increased as the size of primary tumor increased with PR/D seen in 28.5% (2/7) of T4 tumors. Sub-analysis of P/RD in patients who had LN metastases (N1) and in those without known LN metastases (N0 and Nx) did not show significant difference in P/RD. When disease-free survival was compared, there was no statistically significant difference in the two groups. In the 56 patients with pathological LN involvement (N1), all P/RD patients were in RRA+ group (n=48) with no statistical significance (7 (14.58%) vs. 0 (0), p=0.58). On comparing the amount of radioiodine administered to RRA+ patients, there was no trend of higher P/RD with increased doses (p=0.88). Conclusion:Our study found that P/RD was not higher in Stage I DTC patients who did not undergo RRA compared to those who received RRA at a median follow-up of 7.4 years. We confirmed our hypothesis that omission of RRA in Stage I patients was not inferior to RRA regarding disease-free survival and long-term clinical outcome proving it to be a safe and reasonable clinical decision to omit RRA. Presentation Date: Saturday, June 17, 2023