Genetic alterations in human pancreatic cancer

Genomic and transcriptional alterations of cholangiocarcinoma

Cholangiocarcinoma (CCA) is one of the representative cancers refractory to any therapeutic approach. The incidence of CCA is highest in the northeastern part of Thailand, where chronic inflammation caused by liver fluke (Opisthorchis viverrini: Ov) infection is a major etiologic factor. The incidence of CCA is also increasing in other countries, including Japan. Here, we overview the genetic and transcriptional alterations of CCA with and without association with Ov infection. CCA with Ov shows enhanced expression of the genes involved in xenobiotic metabolism and chronic inflammatory responses, including cytokine signaling, whereas CCA without Ov shows enhanced expression of growth factor signaling, such as HER2. Exome and the following prevalence sequencing identified mutations of the BAP1, ARID1A, IDH1 and IDH2 genes in CCA, in addition to the high incidence of known mutations in the TP53, KRAS2 SMAD4, and CDKN2A genes, suggesting the role of chromatin modulators in CCA pathogenesis. CCA with Ov shows significantly higher incidence of the TP53 gene mutation, whereas CCA without Ov showed significantly more frequent mutations of the BAP1, IDH1 and IDH2 genes. However, CCAs with Ov and without Ov share a similar mutation spectrum dominated by C : G > T : A transitions mainly at CpG dinucleotides, suggesting that CCA shares etiologic factors with pancreatic ductal carcinoma but not with hepatocellular carcinoma. Comprehensive analyses of the genetic and transcriptional alterations of CCA with and without Ov infection would provide useful information for the prevention, early diagnosis, and treatment of CCA.

Molecular pathology of invasive carcinoma

Abnormalities of several oncogenes and tumor suppressor genes have been identified in carcinomas of the pancreas during the last decade, and multiple genetic changes have been demonstrated in individual carcinomas. The variety of genetic changes suggests that multiple etiologic factors contribute to carcinogenesis in the pancreas. Several of these changes are characteristically found in specific types of tumors, suggesting that different causes and molecular mechanisms are involved. One example is the loss of heterozygosity at the von Hippel-Lindau (VHL) gene locus in both wild type and hereditary serous cystadenomas, and another is the virtual absence of K-ras mutation and p53 abnormalities in acinar cell carcinomas, whereas both are frequently found in ductal adenocarcinomas. Multiple lines of evidence place K-ras mutation very early and loss of p53 and p16 as late events during ductal cell carcinogenesis. The timing and order of other genetic changes such as loss of the DPC4 tumor suppressor function is less certain.

Accumulation of genetic alterations and their significance in each primary human cancer and cell line

Analyses of multiple genetic alterations accumulated in each cancer cell is expected to provide useful information to elucidate the molecular mechanisms involved in tumorigenesis. Here, we summarized the results of studies on aberrations of oncogenes and tumor suppressor genes by ourselves and other groups. DNAs analyzed were from particular sets of surgical specimens from human tumors and cancer cell lines derived from non-small cell lung cancers, pancreatic cancers, hepatocellular carcinomas and gliomas. Tumors could be grouped into two types based on the genetic alterations detected. Tumors in group 1 had mutations in genes encoding proteins involved in a limited number of signal transduction cascades such as p16-cyclin D1/CDK4-RB or MDM2-p53-p21, where the aberration of one component seems to be sufficient to cause dysfunction of the cascade. Group 2 contained a subset of tumors in which no alteration was detected in the genes analyzed, even in the advanced stage or established cancer cells, indicating the involvement of completely different oncogenic pathways.

Increased telomerase activities in human pancreatic duct adenocarcinomas

Telomerase is a key enzyme with regard to immortalization of cancer cells and increased activity has been demonstrated in various human malignant neoplasms. Since little is known of its role in pancreatic cancers, we investigated changes in telomerase activity in human pancreatic duct adenocarcinomas and compared the frequency of increased telomerase activity with the presence of K-ras gene mutations. The samples were obtained from 38 pancreatic duct adenocarcinomas and 7 tumor surrounding tissues at surgical resection. Telomerase activity was examined by telomeric repeat amplification protocol assay and terminal restriction fragment (TRF) length was examined by Southern analysis. K-ras mutation was examined by means of polymerase chain reaction-single strand conformation polymorphism analysis. Among 38 pancreatic carcinomas, 32 (84%) exhibited increased telomerase activities with no apparent relation to the histological type of tumor, tumor size, regional lymphnode involvement and distant metastasis or clinical stage. In tissue surrounding the tumor, telomerase activity was not detected. TRF length tended to be reduced in pancreatic carcinomas. Mutations of K-ras gene were found in 24 out of the 38 (63%) cases. Among the 38 cases, 14 showed increased telomerase activity without K-ras mutation and 4 cases showed K-ras mutation without telomerase activity. These results suggest that increased telomerase activity might be a sensitive genetic diagnostic marker and could be a target for future therapy of pancreatic duct carcinomas.