Genetics of Pancreatic Cancer

Familial pancreatic cancer

BACKGROUND

For many years anecdotal case reports have suggested that pancreatic cancer aggregates in some families.

METHODS

Two recent advances have established that this is in fact the case. First, large registries, such as the National Familial Pancreas Tumor Registry (NFPTR) at Johns Hopkins, have identified a number of families in which multiple family members have been diagnosed with pancreatic cancer. As a result, the patterns of inheritance of pancreatic cancer can now be studied on a scale not possible before. Second, advances in molecular genetic techniques make it possible to test members of these families for germline mutations in known candidate cancer causing genes. As a result, some of the genetic alterations responsible for the familial aggregation of pancreatic cancer have been identified in some families.

RESULTS

The NFPTR has enrolled 362 families in which at least one family member has been diagnosed with pancreatic cancer. These include 151 families in which at least two first-degree relatives have been diagnosed with pancreatic cancer. Analysis of these families has revealed that even second-degree relatives of patients from these families are at increased risk of developing pancreatic cancer. In addition, a number of kindreds which exhibit aggregation of cancer have been tested for germline mutations in known cancer causing genes. Germline mutations in BRCA2 have been shown to predispose to both breast and pancreatic cancer, germline mutations in p16 to melanoma and pancreatic cancer (the FAMMM syndrome), and genetic mutations in STK11/LKB1 to pancreatic cancer in patients with the Peutz-Jeghers Syndrome (PJS).

CONCLUSIONS

Pancreatic cancer aggregates in some families, and relatives of patients with pancreatic cancer have an increased risk of developing pancreatic cancer themselves. The genetic basis for the familial aggregation of pancreatic cancer has been shown to be germline mutations in known cancer causing genes in some of these families.

Role of tumour markers, cytogenetics

A review is presented on the role of conventional and molecular tumour markers (TM) in diagnosis and monitoring of patients with biliopancreatic malignancies. For biliopancreatic malignancy, following CEA as more historical and basic TM of gastrointestinal diseases, the mainstay marker is CA 19-9 as monosialo-ganglioside/glycolipid and sialyl derivative of lacto-N-fucopentaose II (sialyl-Lewis(a), hapten of human Lewis(a) bloodgroup determinant). It is detected in serum of healthy individuals at low concentration < 40 U/ml, with lower and often transitional elevation in benign hepatobiliary diseases and with highest levels in excretory ductal pancreatic adenocarcinoma (s = 70%-95%, sp = 72%-90%), biliary (s = 55%-79%), hepatocellular and cholangiocellular cancer (s = 22%-51%) besides gastric, colorectal and ovarian cancer and occasionally in lung, breast and uterine cancer. Physiologically elevated concentrations in healthy individuals have to be considered in all sorts of secretions (e.g. sputum, saliva, bronchial/gastric secretions, bile juice) of individuals with Lewis(a)-positive secretor status in contrast with low or lacking serum levels of CA 19-9 in patients with Lewis(a-/b-) status (7%-10% of population). In biliopancreatic malignancies, especially pancreatic cancer, CA 19-9 correlates well with clinical course of disease following surgical, chemo- or radiotherapy by a quick normalisation within 2-4 weeks after complete surgery, a transient decrease with successful palliative therapy and an often anticipated increase (lead time up to 6 months) before clinical detection in case of relapse or progressive disease. From CA 19-9 related TM tests some are detecting in addition to sialyl-Lewis(a) (sialyllacto-N-fucopentaose II) also the non-fucosylated precursor sialyl-Lewis(c) (sialyllacto-N-tetraose: CA 50, CA 242, Span-1) solely detected by the DUPAN-2 test and independent of the Lewis(a) secretor status. Some other markers comprise in addition to sialyl-Lewis(a) partially the non-sialylated Lewis(a) antigen (CA 195, CAM 43, CA 494) or are less related (CAM 17.1). The initial phase of screening and early detection is hoped to be better assessed by using molecular markers detecting gene mutations (p53, K-ras), growth factors (EGF, TGF-alpha, TGF-beta, HB-EGF, a/bFGFs, KGF) and growth factor receptor alterations (EGFr, c-erbB2/3/4). From these, K-ras mutations detected in blood, stool and bile juice of patients at risk for pancreatic cancer seem to be more promising than p53 alterations as a more later step in carcinogenesis, although they are neither yet well established nor standardised by reliable assays. In contrast growth factor and growth factor receptor alterations mainly concerning signal transducing systems seem to reflect increased tumour aggressiveness, thus shorter survival and poorer prognosis thereby contributing in the selection of patients for more aggressive therapy.

Molecular genetics and related developments in pancreatic cancer

Cancer of the pancreas is a genetic disease. The most common genetic alterations identified to date in pancreatic cancer are activation of the K-ras oncogene (approximately 90%) and inactivation of the p16 (approximately 95%), p53 (50% to 75%), DPC4 (55%), and BRCA2 (7%) tumor suppressor genes. An understanding of the molecular genetics of carcinoma of the pancreas is important because it may help explain the aggregation of pancreatic cancer in families and may lead to the development of novel tests to detect early cancers. For example, the aggregation of pancreatic cancer in some families has been shown to result from inherited mutations in cancer-causing genes, and genetic alterations shed from pancreatic cancers have been detected in stool specimens. In addition, we believe that an improved knowledge of the molecular genetics of pancreatic cancer will lead to the development of a new generation of rational and more effective treatments.

Strategies for the detection of disease genes in pancreatic cancer

The present review summarizes our strategies aimed at identifying and characterizing genetic alterations occurring at the transcriptional and chromosomal level in pancreatic cancer. To study transcriptional alterations we have used a number of techniques including modified versions of differential hybridizations and cDNA RDA (representational difference analysis). These approaches have led to the identification of more than 500 genes with differential expression in pancreatic cancer. To study chromosomal aberrations occurring in pancreatic cancer tissues we used comparative genomic hybridization (CGH). This allowed the identification of a number of chromosomal regions containing putative tumor suppressor genes or oncogenes. Genes isolated in both approaches represent potential new disease genes for pancreatic cancer and are at present being characterized by individual or serial analysis.

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.

Pancreatic cancer: development of a unifying etiologic concept

Our knowledge of the etiology of all forms of cancer including pancreatic cancer has improved dramatically in the second half of this century. The current model describes a gradual change from a normal pancreatic cell to a fully malignant cell requiring several stages with gradual and progressive alterations appearing at the genetic and the tissue level. Although there are many germ line diseases that are associated with pancreatic cancer it is probable that inherited diseases account for only about 10% of the total burden of pancreatic cancer. Avoidance of smoking and dietary modification are the current best strategies for reducing the risk of this tumor. In addition, newer molecular techniques and imaging procedures should provide clinicians with the ability to detect pancreatic cancer at an early, potentially curable stage.

Molecular genetics of gastrointestinal malignancies

OBJECTIVES

To review the genetic model of colon cancer formation and the primary advances and clinical relevance of molecular genetics of pancreatic cancer and other gastrointestinal malignancies.

DATA SOURCES

Research studies, review articles, and textbook chapters.

CONCLUSIONS

Genetic discoveries are influencing the screening and treatment of colorectal cancer and other gastrointestinal malignancies by better targeting chemoprevention and treatment in high-risk and molecular-distinct patient populations.

IMPLICATIONS FOR NURSING PRACTICE

A basic knowledge of cancer genetics and the latest genetic discoveries will assist oncology nurses in patient teaching, counseling, and care.

Molecular metastases in stage I pancreatic cancer: improved survival with adjuvant chemoradiation

BACKGROUND

Reports of improved survival rates for patients with resected adenocarcinoma of the pancreas coincide with the adoption of adjuvant chemoradiation protocols. The impact of nodal micrometastases demonstrated by molecular assays and adjuvant therapy on survival of patients with stage I pancreatic cancer has not been adequately assessed.

METHODS

A retrospective analysis of postoperative chemoradiation on survival in 61 patients undergoing resection of pancreatic adenocarcinomas from 1984 to 1997 was performed. Archival tumors and regional nodes from 25 patients with stage I cancers were tested for a Kiras oncogene mutation using polymerase chain reaction and analysis for restriction fragment length polymorphisms (PCR/RFLP).

RESULTS

Adjuvant chemoradiation was associated with improved survival for stage I (P < .01), but not stage III, disease. Seventeen (68%) of 25 patients with stage I disease tested had evidence of mutant Kiras in one or more regional nodes. Survival did not differ for patients with molecular micrometastases. Six of 17 (35%) patients with micrometastases received adjuvant chemoradiation and had improved survival (P < .05).

CONCLUSIONS

The majority of patients with stage I pancreatic cancer have PCR/RFLP evidence of lymph node micrometastases. Adjuvant chemoradiation improves survival in these patients by treating micrometastases not detected by histology. Adjuvant chemoradiation should be used for patients with stage I pancreatic cancers.