Table 1. Summary of Key Questions and Recommendations.

Key Question	Recommendation
1. What are the indications for AS in thyroid cancer?	[1-1] When AS is considered as a management strategy for thyroid cancer, the appropriateness of AS should be evaluated
	[1-2] AS can be considered for adult patients with low-risk PTMC (≤1 cm) as an alternative to immediate surgery. Immediate surgery is recommended for high-risk PTMCs
	[1-3] AS is primarily considered for Bethesda V or VI thyroid nodules on FNA or CNB, without suspicious imaging features of gross ETE (particularly the trachea and RLN), LNM, and distant metastasis. However, taking patient preference into account, AS can also be considered for highly suspicious (K-TIRADS 5) thyroid nodules on US without biopsy
2. What is the appropriate US evaluation for patients with PTMC when considering the initiation of AS?	[2-1] Prior to the initiation of AS for thyroid cancer, high-quality US of the thyroid and neck should be performed by experts in thyroid and neck US imaging
	[2-2] CT of the neck may play a supplementary role in the detection of additional LNM in low-risk PTMC
	[2-3] Chest CT is not routinely indicated before AS of low-risk PTMC
3. How should US evaluation of ETE and LNM be performed?	[3-1] Paratracheal tumors abutting the trachea or posteromedial subcapsular tumors should be carefully evaluated for the risk of gross ETE, especially with respect to the trachea and RLN
	[3-2] Anterior subcapsular tumors with strap muscle replacement, paratracheal tumors abutting ≥90° to the trachea, posterior paratracheal tumors without normal intervening parenchyma, and posterior subcapsular tumors with protrusion pose a high risk of gross ETE and immediate surgery should be considered
	[3-3] FNA with thyroglobulin testing should be performed for any suspicious LNs
4. What is the appropriate US imaging technique for evaluating thyroid nodules under AS?	[4-1] We recommend using consistent measurement methods throughout the initial and follow-up examinations during AS
	[4-2] Measurement for three axes should be performed during AS using the same imaging plane and slice as previously measured
5. How should tumor progression be evaluated by US imaging?	[5-1] Tumor progression can be assessed by evaluating tumor size enlargement and new US features of potential gross ETE or LNM
	[5-2] Tumor size enlargement can be assessed by measuring the maximal tumor diameter increase of ≥3 mm or increase of ≥2 mm in at least two dimensions
6. What is the appropriate interval between US examinations during AS?	[6] US evaluations of changes in tumor size and the appearance of novel potential gross ETE and LNM are recommended every 6 months for the first 1–2 years after the initiation of AS and once a year thereafter if no tumor progression is detected
7. When should a conversion to surgery be considered during follow-up?	[7] Surgical conversion can be considered when the PTMC grows to 13 mm (or 12 mm in two dimensions) or when new features inappropriate for AS appear

AS = active surveillance, ETE = extrathyroidal extension, FNA = fine-needle aspiration, K-TIRADS = Korean Thyroid Imaging Reporting and Data System, LNM = lymph node metastasis, PTMC = papillary thyroid microcarcinoma, RLN = recurrent laryngeal nerve, US = ultrasound