Objectives

This study investigates the prognostic impact of lymph node metastases (LNM) detected on post-therapy 131I single photon emission computed tomography/computed tomography (SPECT/CT) in patients with differentiated thyroid cancer (DTC).
It categorizes LNM based on size (<1 cm, ≥1 cm) and 131I uptake.
It analyzes the effect of LNM characteristics and subsequent treatment (reoperation vs. radioiodine therapy (RAI)) on complete response (CR) and progression-free survival (PFS).

Methodology

Retrospective analysis of 942 DTC patients who underwent cervical 131I SPECT/CT after their first RAI.
LNM were categorized based on CT (enlarged ≥1 cm, small <1 cm) and 131I uptake (positive or negative).
Kaplan-Meier curves and Cox regression were used to analyze CR and PFS.

Patients with no LNM had a shorter median time to CR (9.4 months) than those with LNM (44 months, HR 2.2; p<0.01) and a lower risk of progression (median PFS not reached, HR 0.46; p<0.01).
Among patients with LNM, those with enlarged 131I negative LNM had the longest time to CR (24 months, HR 0.36; p<0.01).
Patients with small LNM had a PFS similar to patients without LNM (median PFS not reached, HR 1.22; p=0.54).
Reoperation after first RAI (13.5 months) led to earlier CR than second RAI (median not reached) in patients with enlarged LNM.
For small LNM, second RAI was associated with longer PFS than reoperation (38.4 months vs. not reached, HR 4.0; p=0.02).

The study is limited by its retrospective design, although the large cohort size is a strength. The single-reader image analysis introduces potential bias, and an interobserver comparison would strengthen the findings.
The definition of pathological 131I uptake, while using a reference organ (salivary glands), is novel and its validity in DTC requires further investigation.
The lack of contrast-enhanced CT limits the diagnostic power of the CT component.
The study did not incorporate biochemical markers like Thyroglobulin (Tg), which are important prognostic indicators in clinical practice. Future studies should integrate both imaging and biochemical data.
The small number of patients in the enlarged 131I-negative LNM subgroup (n=22) limits the conclusions that can be drawn regarding treatment decisions for this group.