Background: Papillary thyroid microcarcinoma (PMC; <or=1 cm) is thought to take a benign course during the lifetime. However, recent studies showed high recurrence rates for PMC.
Methods: We analyzed the clinicopathological features, long-term prognosis, and some molecular characteristics including BRAF(V600E) mutation by retrospectively reviewing the records of 1150 patients with papillary thyroid carcinoma (PTC), 278 with PMC, and 868 with PTC >1 cm.
Results: The prevalence of extrathyroidal invasion (52.2%) and initial nodal metastasis (34.9%) in patients with PMC was surprisingly high and almost as high as that for patients with PTC (72.4% and 51.8%, respectively). The rate of recurrent or persistent disease did not differ between patients with PMC and PTC (recurrent or persistent disease, 6.1% vs 14.1%; 53.4- vs 84.2-month follow-up; n = 98 vs 647; corrected p = .112). The frequency of BRAF(V600E) mutation was similar in patients with PMC and PTC (65.6% vs 67.2%). Immunohistochemical staining showed no different expression pattern according to the tumor size.
Conclusion: These results suggest that PMC is not an occult cancer and it can act like larger PTC. Therefore, PMC should not be underestimated in practice.