Clinicopathological Significance and Prognosis of Medullary Thyroid Microcarcinoma: A Meta-analysis

The objective of the present meta-analysis was to evaluate the clinicopathological significance and prognosis of micro-MTC compared to macro-MTC.

Relevant articles were obtained by searching the PubMed and MEDLINE databases. A meta-analysis was performed using 15 eligible studies. In addition, subgroup analysis based on heredity was performed in patients diagnosed with micro-MTC.

The rate of extrathyroidal extension of micro-MTC [0.118 (95% CI 0.073-0.185)] was significantly lower than that of macro-MTC [0.303 (95% CI 0.224-0.395)]. Micro-MTC [0.229 (95% CI 0.161-0.314)] had a significantly lower rate of cervical lymph node (LN) metastasis compared to macro-MTC [0.595 (95% CI 0.486-0.694)]. The rate of multifocality was not significantly different between micro-MTC and macro-MTC [0.394 (95% CI 0.244-0.566) vs. 0.320 (95% CI 0.234-0.421), respectively]. The rate of distant metastasis did not differ significantly between micro-MTC [0.082 (95% CI 0.017-0.314)] and macro-MTC [0.068 (95% CI 0.009-0.376)]. Patients with micro-MTC showed significantly higher disease-free survival rates [hazard ratio [HR] 0.406 (95% CI 0.288-0.575), I ² = 40.563%] compared to patients with macro-MTC.

Micro-MTC has aggressive features, such as multifocality and distant metastasis, similar to macro-MTC and a non-negligible rate of extrathyroidal extension and cervical LN metastasis. We suggest that treatment of micro-MTC should be approached with a similar focus as that of macro-MTC. Considering that less extrathyroidal extension and cervical LN metastasis occur in patients with micro-MTC compared to macro-MTC, we propose that treatment of micro-MTC, which has a relatively low disease burden status, should be viewed as an opportunity for improving prognosis.