Molecular analysis of PIK3CA, BRAF, and RAS oncogenes in periampullary and ampullary adenomas and carcinomas.

BACKGROUND: Mutations of KRAS are known to occur in periampullary and ampullary adenomas and carcinomas. However, nothing is known about NRAS, HRAS, BRAF, and PIK3CA mutations in these tumors. While oncogenic BRAF contributes to the tumorigenesis of both pancreatic ductal adenocarcinoma and intraductal papillary mucinous neoplasms/carcinomas (IPMN/IPMC), PIK3CA mutations were only detected in IPMN/IPMC. This study aimed to elucidate possible roles of BRAF and PIK3CA in the development of ampullary and periampullary adenomas and carcinomas.
METHODS: Mutations of BRAF, NRAS, HRAS, KRAS, and PIK3CA were evaluated in seven adenomas, seven adenomas with carcinoma in situ, and 21 adenocarcinomas of the periampullary duodenal region and the ampulla of Vater. Exons 1 of KRAS; 2 and 3 of NRAS and HRAS; 5, 11, and 15 of BRAF; and 9 and 20 of PIK3CA were examined by direct genomic sequencing.
RESULTS: In total, we identified ten (28.6%) KRAS mutations in exon 1 (nine in codon 12 and one in codon 13), two missense mutations of BRAF (6%), one within exon 11 (G469A), and one V600E hot spot mutation in exon 15 of BRAF. BRAF mutations were present in two of five periampullary tumors. All mutations appear to be somatic since the same alterations were not detected in the corresponding normal tissues.
CONCLUSION: Our data provide evidence that oncogenic properties of KRAS and BRAF but not NRAS, HRAS, and PIK3CA contribute to the tumorigenesis of periampullary and ampullary tumors; BRAF mutations occur more frequently in periampullary than ampullary neoplasms.