title: High prevalence of RAS mutations in RET-negative sporadic medullary thyroid carcinomas.
abstract: BACKGROUND
  Sporadic medullary thyroid carcinomas (MTC) frequently harbor mutations in the RET protooncogene. We have earlier reported a series of 51 sporadic MTC with 64.7% of RET-positive and 35.3% of RET-negative cases.
  
  
  OBJECTIVE
  In the present study, we investigated the possible involvement of RAS and BRAF protooncogenes in the development of sporadic RET-negative MTC.
  
  
  METHODS
  We performed PCR amplification and sequencing analysis of the three mutational hotspots (codons 12, 13, and 61) of the H-, K-, and N-RAS genes, and of the mutational hotspot (codon 600) and exon 11 of the BRAF gene in 65 sporadic MTC, of which 40 were RET positive and 25 were RET negative.
  
  
  RESULTS
  Somatic H-RAS and K-RAS mutations were detected in 14 of 25 (56.0%) and three of 25 (12.0%) of RET-negative sporadic MTC, respectively. On the other hand, only one of 40 (2.5%) RET-positive sporadic MTC had a RAS mutation, namely in H-RAS. One of the H-RAS mutations was novel (c.32_37dupCCGGCG). No mutations of N-RAS or BRAF were detected in all assessed tumor samples.
  
  
  CONCLUSIONS
  Overall, our results showed that RAS mutations were present in 68.0% (17 of 25) of the RET-negative MTC and in only 2.5% of the RET-positive MTC (P < 0.0001), suggesting that activation of the protooncogenes RAS and RET represents alternative genetic events in sporadic MTC tumorigenesis.
authors.affiliation: Centro de Investigação de Patobiologia Molecular, Instituto Português de Oncologia de Lisboa Francisco Gentil E.P.E., Rua Prof. Lima Basto, 1099-023 Lisboa, Portugal. mmoura@ipolisboa.min-saude.pt
authors.forename: Margarida M
authors.initials: MM
authors.lastname: Moura
authors.forename: Branca M
authors.initials: BM
authors.lastname: Cavaco
authors.forename: António E
authors.initials: AE
authors.lastname: Pinto
authors.forename: Valeriano
authors.initials: V
authors.lastname: Leite
mesh_terms: D002116:Calcitonin / Q000097:blood; D018276:Carcinoma, Medullary / Q000235:genetics* / Q000473:pathology; D003062:Codon / Q000235:genetics; D004247:DNA / Q000235:genetics; D004252:DNA Mutational Analysis; D005091:Exons / Q000235:genetics; D005260:Female; D005434:Flow Cytometry; D011905:Genes, ras / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013964:Thyroid Neoplasms / Q000235:genetics* / Q000473:pathology
chemical_list: D003062:Codon; D002116:Calcitonin; D004247:DNA; D051096:Proto-Oncogene Proteins c-ret; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf