Prognostic Value of Microscopic Lymph Node Involvement in Patients With Papillary Thyroid Cancer

Context: The impact of microscopic nodal involvement on the risk of persistent/recurrent disease (PRD) remains controversial in patients with papillary thyroid carcinoma (PTC). Objective: The goal of the study was to assess the risk of PRD and the 4-year outcome in PTC patients according to their initial nodal status [pNx, pN0, pN1 microscopic (cN0/pN1) or pN1 macroscopic (cN1/pN1)]. Design: We conducted a retrospective cohort study. Patients: The study included 305 consecutive PTC patients referred for radioiodine ablation from 2006 to 2011. Main Outcome Measure: We evaluated the risk of structural PRD and the disease status at the last follow-up. At ablation, persistent disease was consistently assessed by using post-radioiodine ablation scintigraphy combining total body scan and neck and thorax single-photon computed tomography-computed tomography (SPECT-CT) acquisition. Results: Of 305 patients, 128 (42%) were pNx, 84 (28%) pN0, 44 (14%) pN1 microscopic, and 49 (16%) pN1 macroscopic. The 4-year cumulative risk of PRD was higher in pN1 macroscopic than in pN1 microscopic patients (49% vs 24%, P = .03), and higher in pN1 microscopic than in pN0 (12%, P = .01) or pNx patients (6%, P < .001). On multivariate analysis, tumor size of 20 mm or greater [relative risk (RR) 3.4; P = .0001], extrathyroid extension (RR 2.6; P < .003), pN1 macroscopic (RR 4.5; P < .0001), and pN1 microscopic (RR 2.5; P < .02) were independent risk factors for PRD. At the last visit, the proportion of patients with no evidence of disease decreased from pNx (98%), pN0 (93%), and pN1 microscopic (89%) to pN1 macroscopic patients (70%) (P < .0001, Cochran-Armitage trend test). Extrathyroid extension (odds ratio 9.7; P < .0001) and N1 macroscopic (OR 4.9; P < .001) independently predicted persistent disease at the last visit, but N1 microscopic did not. Conclusions: Patients with microscopic lymph node involvement present an intermediate outcome between that observed in pN0-pNx patients and pN1 macroscopic patients. These data may justify modifications to the risk recurrence staging systems.