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.