Abstract
Background/Objectives: There remain several challenges to the acceptance and standardization of active surveillance (AS) in patients with early thyroid cancer. The purpose of this study was to update the evidence of tumor progression outcomes in AS to support resolution of clinical concerns and to examine the effect of follow-up duration, period context such as diagnostic techniques, and tumor size at baseline on outcomes. Methods: PubMed, Web of Science, and Embase were used to search for original articles in English until January 2024. The main outcomes were the pooled proportion of patients who showed tumor growth ≥ 3 mm, metastasis to cervical lymph nodes, and conversion to delayed thyroid surgery. A single-arm meta-analysis was performed using a random-effects model. Results: Fourteen studies with 7291 patients were included in the analysis. Pooled results showed that 5.6% (95% CI: 4.2-7.4) of patients increased tumor diameter by more than 3 mm, 1.1% (95% CI: 0.9-1.4) developed cervical lymph node metastases by clinical diagnosis and 3.6% (95% CI: 3.1-4.2) by pathology, 12.7% (95% CI: 9.9-16.1) of patients converted to delayed surgery, with 31.6% (95% CI: 25.3-38.7) of those conversions being due to tumor progression. Subgroup analysis showed a small difference in the proportion of outcomes by baseline tumor size but no increase in the proportion of tumor progression or conversion to surgery due to other factors. Conclusions: This meta-analysis suggests long-term stability in the proportion of tumor progression in AS and less susceptibility to external influences.