Genotyping of an Italian papillary thyroid carcinoma cohort revealed high prevalence of BRAF mutations, absence of RAS mutations and allowed the detection of a new mutation of BRAF oncoprotein (BRAF(V599lns)).
OBJECTIVE
The genes RET and RAS, and more recently BRAF, have been shown to be frequently mutated in human papillary thyroid carcinomas (PTC). The aim of this study was to genotype for these mutations a cohort of thyroid tumours collected at our institutions.


METHODS
Thyroid tumours removed from 51 subjects were analysed, including 43 PTC and 8 non-PTC tumours [3 follicular adenomas (FA), 4 follicular carcinomas (FTC) and 1 anaplastic carcinoma (AC)].


METHODS
RET/PTC1 and RET/PTC3 expression was evaluated by reverse transcriptase-polymerase chain reaction, whereas screening of BRAF (exon 15) and RAS (HRAS, KRAS2 and NRAS) mutations were performed, respectively, by single strand conformation polymorphism and denaturing high-pressure liquid chromatography.


RESULTS
RET/PTC expressions was positive in 5/43 (11.6%) PTC and in none of the non-PTC tumour. Similarly, BRAF mutations were positive only in PTC, but with a higher prevalence (24/43 positives, 55.8%). All but one BRAF mutation resulted in the prototypic substitution of valine 600 with a glutamic acid. In one case, a somatic in-frame insertion of three bases at codon 599 resulted in the insertion of an additional valine. RET/PTC expression and BRAF mutations were mutually exclusive. Screening of the RAS gene allowed identification of oncogenic mutations in 1/3 (33.3%) FA and 3/4 (75%) FTC. None of the PTCs was positive for RAS.


CONCLUSIONS
These data indicate that BRAF mutations are the most frequent genetic event in PTC and that RAS mutations, besides being a genetic hallmark of follicular tumours, are rare or completely absent in PTC from our area. Together, BRAF mutations and rarer RET rearrangements accounted for a genetic event in two-thirds of PTCs. This study showed a novel and presumably oncogenic mutation of BRAF, which is BRAF(V599Ins).
Carta
Claudio
C
Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Rome, Italy.
Moretti
Sonia
S
Passeri
Lucia
L
Barbi
Flavia
F
Avenia
Nicola
N
Cavaliere
Antonio
A
Monacelli
Massimo
M
Macchiarulo
Antonio
A
Santeusanio
Fausto
F
Tartaglia
Marco
M
Puxeddu
Efisio
E
D000328:Adult; D000368:Aged; D002291:Carcinoma, Papillary / Q000235:genetics*; D015331:Cohort Studies; D004252:DNA Mutational Analysis; D005787:Gene Frequency; D015321:Gene Rearrangement; D005819:Genetic Markers; D005838:Genotype; D006801:Humans; D008875:Middle Aged; D009154:Mutation; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics; D013964:Thyroid Neoplasms / Q000235:genetics*; D018631:ras Proteins / Q000235:genetics*
D005819:Genetic Markers; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D018631:ras Proteins