Portal de Periódicos da CAPES

The Primary Occurrence of BRAF V600E Is a Rare Clonal Event in Papillary Thyroid Carcinoma

2011; Oxford University Press; Volume: 97; Issue: 2 Linguagem: Inglês

10.1210/jc.2011-0618

1945-7197

Anna Guerra, Maria Rosaria Sapio, Vincenzo Marotta, Elisabetta Campanile, Stefania Rossi, Irene Forno, Laura Fugazzola, Alfredo Budillon, Tania Moccia, Gianfranco Fenzi, Mario Vitale,

S100 Proteins and Annexins

BRAFV600E is considered a primary event, a negative prognostic marker, and a site for pharmacological intervention in papillary thyroid carcinoma (PTC). We asked whether BRAFV600E can occur as a subclonal event in PTC and whether this and other oncogenes can coexist in the same tumor. We determined by pyrosequencing the percentage of mutant BRAF, NRAS, and KRAS alleles in a series of conventional PTC. We also analyzed the BRAF mutation status in PTC cell clones in culture. BRAFV600E alleles were present in 41 of 72 PTC (56.9%) in the range 44.7 to 5.1% of total BRAF alleles. In four PTC samples, mutant BRAF alleles were about 50%, being therefore compatible with a clonal heterozygous mutation. In 27 PTC samples, BRAFV600E alleles were in the range of 25 to 5.1%. This finding was confirmed after exclusion of the presence of a large contamination by lymphoreticular cells and by the analysis of PTC cells selected by laser capture. Analysis of clones derived from a single cell confirmed the presence of two distinct PTC populations with wild-type or mutated BRAF. Simultaneous subclonal BRAF and KRAS mutations were demonstrated in two PTC. These data demonstrate that clonal BRAFV600E is a rare occurrence in PTC, although frequently this cancer consists of a mixture of tumor cells with wild-type and mutant BRAF. These results suggest that BRAF mutation in PTC is a later subclonal event, its intratumoral heterogeneity may hamper the efficacy of targeted pharmacotherapy, and its association with a more aggressive disease should be reevaluated.