Multifocality increases the risk of central compartment lymph node metastasis but is not related to the risk of recurrence and death in papillary thyroid carcinoma.

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Multifocality is a distinctive feature of papillary thyroid carcinoma (PTC); however, the biological behavior of PTC and its optimal management strategy remain unclear. The aim of this study was to analyze the clinical features and prognostic differences of multifocal papillary carcinoma and to guide the precise treatment of multifocal papillary carcinoma. The medical records of 1,139 patients with PTC who had undergone total or hemi-thyroidectomy between April and October 2013 at the Tianjin Medical University Cancer Institute and Hospital were reviewed. The number of central compartment lymph node metastasis (LNM), as well as the size, number, and laterality of each tumor focus, along with other possible risk factors were recorded. Patients were followed up until May 2024. According to univariate and multivariable analyses, PTC, multifocality, and male sex were risk factors for level VI LNM. Moreover, the central compartment LNM rate increased proportionally with the number of foci. The LNM rates for patients with unilateral papillary thyroid microcarcinoma (PTMC) having one, two, three, and four foci were 27.8% (146/525), 37.3% (55/142), 40% (14/35), and 57.1% (4/7), respectively; conversely, the LNM rates for patients with bilateral PTC having two, three, four, five, and six foci were 50% (15/30), 62.5% (15/24), 70% (7/10), 83.3% (5/6), and 100% (2/2), respectively. Notably, the LNM rates were comparable for multifocal PTMCs (largest tumor diameter: 6-10 mm) and unilateral unifocal PTCs [44.0% (55/125) vs. 60.8% (59/97); P=0.43 (0.42-0.93)]. Meanwhile, the survival rates and risk of recurrence were comparable for multifocal and unifocal PTCs. Multifocality is indicative of a heightened risk of LNM in PTC but does not increase the risk of recurrence or mortality. Multifocal PTMCs with a tumor diameter of 6-10 mm should undergo thorough preoperative evaluation of the regional lymph nodes as they have a higher risk of developing LNM.