[Invasiveness of papillary thyroid microcarcinoma with BRAF mutation]

To explore the invasiveness of papillary thyroid microcarcinoma(PTMC)with BRAF mutation.

Totally 99 patients with PTMC with BRAF mutation were enrolled in this study, meanwhile another 97 patients with papillary thyroid carcinoma (PTC) (tumor size>1 cm)with BRAF mutation were included as controls. The clinicopathologic factors including extrathyroidal invasion, multifocality, and distant metastasis were analyzed.

The rates of extrathyroidal invasion and nodal metastasis in PTMC group were as high as 16.10% and 71.74%, respectively. In the PTMC group and PTC group,the extrathyroidal invasion rate was 16.10% and 39.18%, cervical lymph node metastasis rate was 71.74% and 91.75%, and distant metastasis rate was 1.01% and 9.28%, respectively. In the PTMC subgroups with tumor sizes ≤0.3 cm, 0.3-0.6 cm, and 0.6-1.0 cm, the cervical lymph node invasion rate was 60.00%, 72.50%, and 73.81%, the extrathyroidal invasion rate was 10.00%, 9.09%, and 24.44%, and the multifocality rate was 60.00%, 38.64%, and 57.78%, respectively. Univariate analysis showed that the tumor size was not significantly correlated with multifocality (Χ (2)=3.752, P=0.153), cervical lymph node metastasis (Χ (2) = 0.780,P = 0.677), extrathyroidal invasion (Χ (2) = 4.182, P = 0.124), and distant metastasis (Χ (2)=1.212, P = 0.545). While the BRAF group and PTC group were not significantly different in multifocality (Χ (2) = 1.742, P=0.187), they were significantly different in terms of extrathyroidal invasion (Χ (2) = 13.000, P = 0.000), nodal involvement (Χ (2) = 12.819, P = 0.000), and distant metastasis (Χ (2) = 5.316, P = 0.021). Multivariate analysis showed that nodal metastasis was independently associated with size>1 cm (P=0.001) and extrathyroidal invasion (P=0.003).

BRAF mutant PTMC manifests relative high extrathyroidal involvement and nodal metastasis, and the similar multifocality as BRAF mutant PTC. Radioactive iodine should be considered in PTMC with the presence of BRAF mutation combined with extrathyroidal invasion or nodal metastasis.