Active Surveillance for Patients With Papillary Thyroid Microcarcinoma: A Single Center's Experience in Korea.

Context: Papillary thyroid microcarcinoma (PTMC) usually has an excellent prognosis.

Objective: To evaluate the three-dimensional structures of PTMCs, using serial neck ultrasonography (US) in patients under active surveillance.

Design and Setting: A retrospective cohort study.

Participants: In total, 192 patients diagnosed with PTMC under active surveillance for >1 year were included in a median 30-month follow-up. Changes in tumor size were evaluated not only using the maximal tumor diameter but also the tumor volume.

Results: The median age of patients was 51.3 years and 145 patients (76%) were female. The median initial maximal tumor diameter and tumor volume were 5.5 mm and 48.8 mm3, respectively. The tumor size increased in 27 patients (14%); 23 patients showed a tumor volume increase >50% without a maximal diameter increase of ≥3 mm. The other four patients had both an increasing tumor volume and increasing maximal tumor diameter ≥3 mm. One patient (0.5%) had newly appeared cervical lymph node (LN) metastasis at 3 years after the initial diagnosis. There were no significant risk factors associated with increased tumor size, such as age, sex, or Hashimoto thyroiditis. Twenty-four patients (13%) underwent delayed thyroid surgery at a median of 31.2 months and seven (29%) had cervical LN metastasis on pathologic examination.

Conclusion: Some PTMCs could grow significantly after a relatively short period of active surveillance. We also found that the change in tumor volume was more sensitive to detect tumor progression than the change in the maximal tumor diameter.