High-sensitivity BRAF mutation analysis: BRAF V600E is acquired early during tumor development but is heterogeneously distributed in a subset of papillary thyroid carcinomas

J Clin Endocrinol Metab. 2014 Aug;99(8):E1530-8. doi: 10.1210/jc.2013-4389. Epub 2014 Apr 29.

Abstract

Context: The homogeneous distribution of BRAF V600E in papillary thyroid carcinoma (PTC) has been called into question by recent reports. These studies claim that BRAF V600E is heterogeneous and is limited to tumor cell subsets in the majority of PTCs.

Objective: The objective of the study was to understand the allele distribution of BRAF V600E by evaluating the percentage of mutated neoplastic cells in a group of PTCs using two different highly sensitive analytical approaches: allele-specific locked nucleic acid PCR and 454 next-generation sequencing targeted to BRAF exon 15.

Study design: BRAF V600E was investigated using allele-specific locked nucleic acid PCR on 155 consecutive samples of PTC. Mutated cases were reanalyzed by 454 next-generation sequencing and immunohistochemistry. Because the evaluation of genetic heterogeneity in tumor samples can be profoundly biased by contamination with normal cells, all mutation frequency data were normalized to the real amount of neoplastic cells within each tumor.

Results: Eighty-five of 155 PTCs (54.8%) were BRAF V600E mutated. The distribution of mutated neoplastic cells within the tumor was as follows: greater than 80% in 37 of 85 (43.5%), 30-80% in 39 of 85 (45.9%), and less than 30% in 9 of 85 (10.6%). In most of the PTCs with less than 80% BRAF V600E-positive neoplastic cells, the mutation was present in large neoplastic cell subpopulations. Tumors with less than 30% mutated neoplastic cells were smaller than tumors with a percentage of mutated cells greater than 80% or between 30% and 80% (P < .05).

Conclusions: BRAF V600E is heterogeneously distributed in some PTCs. The large BRAF V600E neoplastic cell subpopulations found in mutated cases is consistent with the view that the BRAF V600E is acquired early during PTC development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Amino Acid Substitution
  • Carcinoma / epidemiology
  • Carcinoma / genetics*
  • Carcinoma / metabolism
  • Carcinoma / pathology
  • Carcinoma, Papillary
  • Cell Transformation, Neoplastic / genetics*
  • DNA Mutational Analysis / methods
  • Gene Frequency
  • Genetic Heterogeneity*
  • Glutamic Acid / genetics
  • Humans
  • Middle Aged
  • Polymerase Chain Reaction / methods
  • Proto-Oncogene Proteins B-raf / genetics*
  • Thyroid Cancer, Papillary
  • Thyroid Neoplasms / epidemiology
  • Thyroid Neoplasms / genetics*
  • Thyroid Neoplasms / metabolism
  • Thyroid Neoplasms / pathology
  • Valine / genetics
  • Young Adult

Substances

  • Glutamic Acid
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf
  • Valine