Abstract A retrospective review of the tumor focality and BRAF^V600E mutational status of all thyroidectomy cases diagnosed with papillary thyroid carcinoma (PTC) between 1/2010 and 7/2013 was performed. A total of 122 cases were included in this study consisting of 65 solitary cases and 57 multifocal cases with a total of 209 tumor nodules. In the multifocal tumors with absent BRAF^V600E mutation in the dominant nodule, an additional tumor focus was submitted for testing. The clinicopathologic characteristics of the cases were then compared and analyzed. Significant association with BRAF^V600E mutation was driven by previously established unfavorable histologic features such as usual variant, capsular invasion, lymphovascular invasion, extrathyroidal extension, and lymph node metastasis. We did not establish this association with tumor multifocality in this study. Although more cases of mPTC (multifocal papillary thyroid carcinoma) had BRAF^V600E mutation in comparison with the solitary cases (56 vs 44%), we did not find a significant difference between the two groups (p = 0.0689). Furthermore, at least one of the unfavorable histologic features was also noted in three out of the five multifocal cases with discordant mutations in the two largest nodules. The heterogeneity of BRAF^V600E mutational status in mPTC is evident in this study and although it seems prudent to further test additional foci, it appears that in most cases there are already histologic features that support a more aggressive behavior. Selective testing based on histomorphology may be a more practical approach in these cases.
Keywords: papillary thyroid carcinoma; microcarcinoma; solitary; multifocal; BRAF^V600E; mutation; dominant nodule; heterogeneity