Quantification of BRAF V600E alleles predicts papillary thyroid cancer progression

Abstract

The BRAF V600E mutation is the most common genetic alteration in thyroid cancer. However, its clinicopathological significance and clonal mutation frequency remain unclear. To clarify the inconsistent results, we investigated the association between the allelic frequency of BRAF V600E and the clinicopathological features of classic papillary thyroid carcinoma (PTC). Tumour tissues from two independent sets of patients with classic PTC were manually microdissected and analysed for the presence or absence of the BRAF mutation and the mutant allelic frequency using quantitative pyrosequencing. For external validation, the Cancer Genome Atlas (TCGA) data were analysed. The BRAF V600E mutation was found in 264 (82.2%) out of 321 classic PTCs in the training set. The presence of BRAF V600E was only associated with extrathyroidal extension and the absence of thyroiditis. In BRAF V600E-positive tumours, the mutant allelic frequency varied from 8 to 41% of the total BRAF alleles (median, 20%) and directly correlated with tumour size and the number of metastatic lymph nodes. Lymph node metastases were more frequent in PTCs with a high (R20%) abundance of mutant alleles than in those with a low abundance of mutant alleles (PZ0.010). These results were reinforced by validation dataset (nZ348) analysis but were not reproduced in the TCGA dataset. In a population with prevalent BRAF mutations, quantitative analysis of the BRAF mutation could provide additional information regarding tumour behaviour, which is not reflected by qualitative analysis. Nonetheless, prospective studies are needed before the mutated allele percentage can be considered as a prognostic factor.

BRAFwild papillary thyroid carcinoma has two distinct mRNA expression patterns with different clinical behaviors

“…Cluster 1 showed indolent behavior, whereas cluster 2 showed aggressive clinical behavior (Table ). Many previous studies have reported that BRAF V600E mutated PTCs have aggressive clinical behavior . Therefore, we compared cluster 1 with BRAF wild PTCs in cluster 2 to exclude the effect of BRAF V600E mutation in cluster 2 (Table ).…”

“…However, it is absent in the cribriform‐molecular variant type of PTC . The BRAF V600E mutation is known to be correlated with cancer prognosis . Several studies have reported that the presence of BRAF V600E mutation is associated with extrathyroidal extension, tumor size, and the number of metastatic lymph nodes in PTCs .…”

“…The BRAF V600E mutation is known to be correlated with cancer prognosis . Several studies have reported that the presence of BRAF V600E mutation is associated with extrathyroidal extension, tumor size, and the number of metastatic lymph nodes in PTCs . In this regard, some groups have suggested that prophylactic central lymph node dissection should be considered as part of thyroidectomy when BRAF mutation is found in diagnostic fine‐needle aspiration .…”

The thyroid imaging reporting and data system on US, but not the BRAFV600E mutation in fine-needle aspirates, is associated with lateral lymph node metastasis in PTC

“…[11] Previous reports based on surgically resected PTC specimens have shown that a high mutant allelic frequency was associated with disease recurrence or extrathyroidal invasion, [12,30] but only one study reported a significant association with lymph node metastasis. [13] Thus, studies on the association between quantitative measurements of the BRAF V600E mutation from surgical specimens have also shown variable results. In a recent report, we have demonstrated that real-time PCR Ct values for the BRAF V600E mutation in fine-needle aspirates were associated with central lymph node metastasis in papillary thyroid microcarcinoma.…”

“…Nonetheless, there seems to be a correlation between tumor volume and the quantitative expression of the BRAF V600E mutation, as our study showed a weak but significant correlation with BRAF V600E Ct values and tumor size, which is similar to previous studies assessing the mutant BRAF V600E allelic percentage or its relative expression in PTC. [12,13,21,30] …”