Background: The rapid increase in the incidence of small papillary thyroid carcinoma (PTC) appears to be caused by the detection of small thyroid cancers. Active surveillance (AS) was therefore suggested to overcome this problem. As the results were favorable with low rates of size enlargement and lymph metastasis, the 2015 American Thyroid Association Management Guidelines endorsed AS as an alternative to immediate surgery. As the clinical value of AS is a subject of ongoing active discussions and surveys, we considered a systematic review and meta-analysis to be timely and necessary. Methods: Ovid-MEDLINE and EMBASE databases were searched up to January 5, 2019, for studies reporting patients who were followed up with AS for PTC. Data extraction and methodological quality assessment were performed independently by two radiologists. The primary outcomes were to identify the annual pooled proportions of size enlargement of 3 mm or more and the detection of lymph node metastases at a 5-year follow-up period. These were calculated using an inverse-variance weighting model. An additional outcome was evaluation of the reasons for surgery during AS. Results: The pooled proportion of size enlargement occurring at 5 years was 5.3% [95% confidence interval (CI), 4.4-6.4%], and the pooled proportion of 5-year lymph node metastasis was 1.6% [CI, 1.1-2.4%]. In many subjects undergoing delayed operations, the reasons for operation were often other than those of size enlargement or lymph node metastasis. Conclusions: AS is effective for the management of small PTC, with a low proportion of size enlargement or lymph node metastasis occurring at 5 years. However, a substantial proportion of the causes of delayed surgery were other than size enlargement or lymph node metastasis, and these situations need to be optimally managed.
Keywords: active surveillance; papillary thyroid cancer; systematic review and meta-analysis.