Do radioiodine-avid lymph nodes from differentiated thyroid cancer on the initial posttherapy scan need repeated I-131 therapy?

BackgroundResidual/recurrent lymph node metastase (LNM) is often found after differentiated thyroid cancer (DTC) surgery. This study aimed to investigate whether patients complicated with radioiodine-avid (I-131+) lymph nodes from DTC on the initial posttherapy scan (PTS) need repeated I-131 therapy. MethodsFrom June 2013 to August 2022, DTC patients with I-131+ lymph nodes on the initial PTS who received at least two cycles of I-131 therapy were retrospectively enrolled. They were divided into a complete response (CR) group and an incomplete response (IR) group according to their response to the initial I-131 therapy based on the 2015 American Thyroid Association (ATA) guidelines. ResultsA total of 170 DTC patients with I-131+ lymph nodes on the initial PTS were included; 42/170 (24.7%) patients were classified into the CR group and 128/170 (75.9%) were classified into the IR group according to their response to the initial I-131 therapy. None of the 42 CR patients had disease progression at the subsequent follow-up, and 37/170 (21.8%) IR patients improved after repeated therapy. Univariate analysis showed that N stage (P=0.002), stimulated thyroglobulin (sTg) level before initial I-131 therapy (P<0.001), LNM size (P<0.001), number of total residual/recurrent LNM (P=0.021), radioiodine-nonavid (I-131-) LNM (P=0.002) and ultrasound features (P<0.001) were related to the initial treatment response. On multivariate analysis, sTg level (OR=1.186, P<0.001) and LNM size (OR=1.533, P=0.004) were independent risk factors for IR after initial I-131 therapy. The optimal sTg level and LNM size cutoff value for predicting the treatment response after initial I-131 therapy were 18.2 mu g/l and 5mm. ConclusionThis study suggested that approximately one-quarter of patients with I-131+ lymph nodes on initial PTS, especially those with N0 or N1a stage, lower sTg level, smaller LNM size, <= 2 residual/recurrent LNMs, negative ultrasound features and no I-131- LNM, remain stable after one cycle of I-131 therapy and do not need repeated therapy.