Subclonality for BRAF mutation in papillary thyroid carcinoma is associated with earlier disease stage

Context: The presence of driver mutations only in a subset of tumor cells within a single lesion, defined as subclonality, is being appreciated as a clinically significant factor. BRAF mutation is the most common driver mutation in papillary thyroid carcinoma (PTC). There are conflicting data in the literature regarding the presence of BRAF mutation subclonality in PTC and its clinical significance. Objective: The purpose of the present study was to use a molecular and morphometric approach to determine BRAF clonality status and its clinical-pathological correlates. Design: Fifty-nine cases of PTC were studied. DNA extracted from the tumors underwent deep sequencing to determine the percentage of BRAF mutant allele copies. Additionally, we used computerized morphometry to determine the fraction of tumor cells in each sample. Using both variables, we were able to determine the presence or absence of subclonality for BRAF mutation, which was further correlated with clinical, pathological, and prognostic data. Results: BRAF mutation was found in 49 (83%) cases. The average percentage of tumor cells and of BRAF mutant alleles in the samples were 68.1 ± 9.8 and 26 ± 6.7, respectively. Based on the molecular and morphometric analysis, 11 (24%) cases were found to be subclonal for BRAF mutation. Tumors with subclonal BRAF mutations were significantly smaller compared to tumors with clonal mutation (0.82 ± 0.38 cm vs 1.37 ± 0.57 cm, P = .005) and were less likely to have lymph node metastasis (0% vs 32%, P = .03). Conclusions: In PTC, subclonality for BRAF mutation is associated with earlier stage. Molecularmorphometric analysis of PTC can provide clonality information with potential clinical significance.