Prognostic value of microscopic lymph node involvement in patients with papillary thyroid cancer.

Abstract

The impact of microscopic nodal involvement on the risk of persistent/recurrent disease (PRD) remains controversial in patients with papillary thyroid carcinoma (PTC). 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)]. We conducted a retrospective cohort study. The study included 305 consecutive PTC patients referred for radioiodine ablation from 2006 to 2011. 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. 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. 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.