**1. Introduction**

Thyroid cancer is the ninth most prevalent cancer worldwide, and its incidence has dramatically increased over the last four decades [1]. There were 586,202 new cases of thyroid cancer in 2020, and papillary thyroid carcinoma (PTC) represented over 80% of all thyroid cancers [1]. Surgery for thyroid cancer is the most important element of a multifaceted treatment approach [2]. Earlier guidelines recommended total thyroidectomy as the initial surgical treatment option, whereas the latest 2015 American Thyroid Association (ATA) guidelines have endorsed that thyroid lobectomy is safe and sufficient in selected patients with a low to intermediate risk of recurrence [2–4]. The optimal surgical extent can be determined by several clinicopathological factors, including personal history of radiation treatment to the head and neck, familial history of thyroid cancer, tumor size, extrathyroidal extension (ETE), regional or distant metastases, and multifocality [2].

**Citation:** Woo, J.; Kwon, H. Optimal Surgical Extent in Patients with Unilateral Multifocal Papillary Thyroid Carcinoma. *Cancers* **2022**, *14*, 432. https://doi.org/10.3390/ cancers14020432

Academic Editors: Fabio Medas and Pier Francesco Alesina

Received: 13 December 2021 Accepted: 13 January 2022 Published: 15 January 2022

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Multifocality is defined as the simultaneous presence of two or more tumor foci within the thyroid gland [5]. Tumor multifocality is a common finding in PTC, with a prevalence of 18–87% of cases in the literature [6]. Multifocality is considered as a prognostic marker for the progression of PTC [7]. Multifocality has been associated with the high-risk features of PTC, including aggressive histology, ETE, lymph node (LN) involvement, and distant metastasis [7,8]. A recent meta-analysis also indicated that multifocality was an independent predictor of recurrence [9]. Some researchers further suggested that multifocal PTC could increase the risk of cancer-specific and overall mortality [10]. Therefore, more aggressive treatments, including total thyroidectomy and higher-dose radioiodine, are commonly used to treat patients with multifocal PTC [9,11–13].

There is a controversy about the optimal operative extent for patients with multifocal PTC. Several studies demonstrated that total thyroidectomy decreased the risk of recurrence compared with thyroid lobectomy [14–16]. On the contrary, other studies have suggested that lobectomy could be a feasible and valid option for patients with unilateral multifocal PTC [17–20]. These conflicting results are because, at least in part, all previous studies except one investigated the impact of operative extent without adjustment of other risk factors. Only Jeon et al. evaluated the significance of the surgical extent using a multivariable Cox proportional hazards model; however, this study only included patients with tumor size ≤ 1 cm, absence of gross ETE, and node-negative PTC (pT1aN0M0) [19].

Therefore, in the present study, we investigated the effect of the operative extent on the recurrence of multifocal PTC patients with various risk factors.
