Study Protocol of Expanded Multicenter Prospective Cohort Study of Active Surveillance on Papillary Thyroid Microcarcinoma (MAeSTro-EXP) (Endocrinol Metab 2025;40:236-46, Jae Hoon Moon et al.)

Numerous previous studies have reported favorable prognoses for thyroid carcinoma patients, leading clinical guidelines to progressively reduce the extent of surgical resection and narrow surgical indications [1,2]. Recently, the Korean Thyroid Association guidelines on the management of differentiated thyroid cancers also suggested active surveillance for low-risk thyroid carcinoma patients, specifically those with tumors smaller than 1.0 cm, without aggressive subtypes, potential extrathyroidal extension, or cervical lymph node involvement [1]. As accumulating clinical evidence consistently supports the excellent prognosis for patients with low-risk thyroid cancer, the use of active surveillance is likely to increase. However, the upper tumor size limit of 1.0 cm for active surveillance is somewhat arbitrary. Indeed, only a few studies have demonstrated significant differences in clinical outcomes between patients with small tumors (<1.0 cm) and those with slightly larger tumors [3,4]. Therefore, evaluating the safety of active surveillance in papillary thyroid carcinomas, including tumors larger than 1.0 cm, compared to immediate surgery, has considerable clinical relevance. In this context, the Expanded Multicenter Prospective Cohort Study of Active Surveillance on Papillary Thyroid Microcarcinoma (MaeStro-EXP) study [5] holds clinical importance because it investigates the potential for expanding active surveillance indications for patients with low-risk thyroid cancer.

From an ethical perspective, randomly assigning patients to either active surveillance or immediate surgery groups is impossible. Therefore, patients themselves must choose between the two treatment approaches as participants in the study. This decision-making process could introduce selection bias; thus, it is essential that all participants receive consistent clinical information and sufficient time to deliberate. In Korea, family-centered values strongly influence medical decision-making, making it crucial to incorporate family members’ perspectives. This study appropriately considers this cultural factor, which is a significant strength.

Nevertheless, demographic and cultural differences among patients might considerably influence their choice between active surveillance and immediate surgery. Such selection bias could constitute a fundamental limitation, as variations in clinical outcomes between the two groups might result from underlying differences in patient characteristics rather than solely from the treatment modality itself. The authors have appropriately acknowledged this limitation, highlighting the importance of conducting careful and thorough analyses in future stages of the study.

This study holds significant promise, as it may enable more detailed risk stratification among patients with low-risk thyroid cancer. By refining risk criteria, the approach can reduce unnecessary thyroid surgeries, thereby preventing surgery-associated complications and preserving patients’ quality of life. Additionally, it may contribute to a more efficient allocation of healthcare resources across the medical system.