Patterns, predictive factors and prognostic impact of multilevel metastasis in N1b papillary thyroid carcinoma

Background: The patterns, predictive factors and prognostic impact of multilevel metastasis in patients with N1b papillary thyroid carcinoma (PTC) were investigated. Methods: A retrospective review of patients with N1b PTC from a tertiary referral centre in Korea who underwent unilateral modified radical neck dissection was undertaken. Results: Of 658 patients, multilevel metastasis was found in 73·9 per cent; the most common type was metastasis in two levels. Tumour size per 0·1-cm increment (adjusted odds ratio (OR) 1·33, 95 per cent c.i. 1·08 to 1·64), microscopic extrathyroidal extension (adjusted OR 1·72, 1·10 to 2·71), gross extrathyroidal extension (adjusted OR 2·35, 1·24 to 4·46), unilateral central lymph node metastasis (adjusted OR 2·45, 1·53 to 3·92) and bilateral central lymph node metastasis (adjusted OR 4·06, 2·29 to 7·18) were independent predictors of multilevel metastasis. Only four-level metastasis significantly increased the risk of overall locoregional recurrence (LRR) (adjusted hazard ratio (HR) 7·41, 95 per cent c.i. 2·20 to 24·53) and lateral neck LRR (adjusted HR 7·22, 1·82 to 28·65), compared with one-level metastasis. Two subgroup analyses were conducted, showing that only three-level metastasis including metastasis in level V significantly increased the risk of overall LRR (adjusted HR 5·66, 1·20 to 26·75). In addition, having level V metastasis was an independent predictor of both overall (adjusted HR 3·26, 1·72 to 6·18; P < 0·001) and lateral neck (adjusted HR 3·28, 1·50 to 7·16; P = 0·003) LRR. Conclusion: Level V metastasis rather than multilevel metastasis itself is associated with an increased risk of LRR. Patients with N1b PTC and level V metastasis require risk restratification and meticulous follow-up.