*2.2. Participant Selection*

Patients were included in the present study if they were 20 years or older, had a pathologic diagnosis of unilateral multifocal PTC, and underwent curative-intent surgical treatment, including thyroid lobectomy or total thyroidectomy. The medical record of each patient was reviewed for clinicopathological data. Patients were excluded if they had high-risk histologic subtypes (including diffuse sclerosing, tall cell, and hobnail variants), gross ETE, or distant metastasis. Patients with incomplete data were also excluded. Data on patient demographics and tumor characteristics, including tumor size, microscopic ETE, LN metastasis, resection margin involvement, and coexisting Hashimoto thyroiditis, as well as recurrence status, were collected. The American Joint Committee on Cancer 7th edition was used for pathologic tumor, node, metastasis (TNM) staging.
