Analysis of the clinicopathologic features of papillary thyroid microcarcinoma based on 7-mm tumor size

Background: We examined the clinicopathologic features of papillary thyroid microcarcinomas (PTMCs) measuring ≤7 mm and compared them with those of PTMCs >7 mm. Methods: Between January 2007 and June 2009, a total of 275 patients with PTMCs underwent surgery. They were divided into two groups. Group I included patients with tumors ≤7 mm, and group II included those with tumors >7 mm but ≤10 mm. We compared the two groups' clinicopathologic features. Results: Total thyroidectomy was more often performed in group II (p = 0.003). Central lymph node metastases were identified in 30.6% of the patients in group I and in 47.8% of the patients in group II (p = 0.005). A statistically significant difference between the two groups was also found for capsule invasion (p < 0.0001), extrathyroidal extension (p = 0.005), and lymphovascular invasion (p = 0.025). On the multivariate analysis, central lymph node metastasis was the only independent factor associated with tumor size. Conclusion: A PTMC ≤7 mm is less likely to have aggressive features, including central lymph node metastasis, capsule invasion, extrathyroidal extension, and lymphovascular invasion, than a PTMC >7 mm. Because the aggressiveness of PTMC was found mainly in the patients with tumors >7 mm, we think that a cutoff value of 7 mm may be considered the threshold of aggressiveness of PTMCs.