The relationship between lateral cervical lymph node positivity rate and recurrence after comprehensive treatment in differentiated thyroid carcinoma: a single-center retrospective cohort study from China

Introduction The lateral cervical lymph node positivity rate has been hypothesized to correlate with the recurrence risk in differentiated thyroid carcinoma (DTC) patients. However, the extent of this association within the Chinese population remains understudied. This study seeks to elucidate the potential causal link between the lymph node positivity rate and DTC recurrence. Methods We conducted a retrospective cohort study, examining clinical records of 4,731 DTC patients who received surgical treatment at the First Medical Center of the General Hospital of the Chinese People's Liberation Army from January 2015 to May 2020. The study variables encompassed demographic and clinical characteristics, including sex, age, tumor size, location, laterality, capsular invasion, lymph node metastasis counts, lymph node positivity rates, histological subtypes, Hashimoto's thyroiditis co-occurrence, and the timing of iodine-131 therapy post-surgery. After applying strict inclusion criteria, 1,074 patients were selected for analysis. Recurrence was defined as structural incomplete response (SIR), confirmed by imaging or histological means. The lymph node positivity rate was calculated as the proportion of positive lymph nodes to the total lymph node count. Results Multivariate analysis revealed a nonlinear association between the lateral cervical lymph node positivity rate and post-treatment recurrence, with a significant threshold at 0.5. The recurrence risk was substantially elevated with a positivity rate below this threshold (HR: 27.48, 95% CI: 7.21-104.70, P<0.0001), while no significant association was observed above it (HR: 0.17, 95% CI: 0.02-1.57, P=0.119). Subgroup analysis within the high-risk cohort did not yield a significant association between the positivity rate and recurrence risk (HR=0.43, 95% CI: 0.10-1.79, P=0.246). Discussion In conclusion, this study identifies a nonlinear relationship between the lateral cervical lymph node positivity rate and the risk of DTC recurrence post-treatment. A positivity rate of less than 0.5 is positively associated with recurrence, while this association diminishes in significance among high-risk patients. This differs from the results previously reported. Further studies are needed to determine the potential mechanisms of the associations observed in observational studies.