Risk stratification of lateral neck recurrence for patients with pN1a papillary thyroid cancer

Background Lateral neck is not recommended for dissection in patients with pN1a papillary thyroid cancer (PTC), but its recurrence risk has not been well stratified. We aimed to develop a risk stratification system for lateral neck recurrence in patients with pN1a PTC. Methods Patients with pN1a PTC who underwent thyroidectomy and unilateral central compartment dissection from 2000–2016 were enrolled. The association between number of central lymph node metastases (CLNMs) and lateral neck recurrence was comprehensively assessed using a Cox proportional hazards model with restricted cubic spline. Stratification was then performed based on CLNMs and other significant risk factors selected by multivariate analysis. Lateral neck recurrent-free survival (LRFS) rate of each stratification was estimated with Kaplan–Meier curve and comparison was performed using log-rank test. Results Ninety-six (3.8%) lateral neck recurrences were identified during a median follow-up of 62 months among a total of 2500 admitted cases. An increasing number of CLNMs was associated with compromised LRFS for up to 6 CLNMs ( P < 0.001), and CLNMs > 3 indicated significantly worse 5-year LRFS than that of CLNM ≤ 3 (90.6% vs. 98.1%, P < 0.001). When stratification with CLNMs and primary tumor size (selected by multivariate analysis, HR (95%CI) = 4.225(2.460–7.256), P < 0.001), 5-year LRFS rates of high- (CLNMs > 3 and primary tumor size > 2 cm), intermediate- (CLNMs > 3 and primary tumor size 1–2 cm) and low-risk (primary tumor size ≤ 1 cm or CLNMs ≤ 3) groups were 78.5%, 90.0% and 97.9%, respectively ( P < 0.05). Conclusions The number of CLNMs combined with primary tumor size seems to effectively stratify lateral neck recurrence risk for patients with pN1a PTC.