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.