Loss of heterozygosity of chromosome 16q in gallbladder carcinoma

Gallbladder cancer epidemiology, pathogenesis and molecular genetics: Recent update

Gallbladder cancer is a malignancy of biliary tract which is infrequent in developed countries but common in some specific geographical regions of developing countries. Late diagnosis and deprived prognosis are major problems for treatment of gallbladder carcinoma. The dramatic associations of this orphan cancer with various genetic and environmental factors are responsible for its poorly defined pathogenesis. An understanding to the relationship between epidemiology, molecular genetics and pathogenesis of gallbladder cancer can add new insights to its undetermined pathophysiology. Present review article provides a recent update regarding epidemiology, pathogenesis, and molecular genetics of gallbladder cancer. We systematically reviewed published literature on gallbladder cancer from online search engine PubMed (http://www.ncbi.nlm.nih.gov/pubmed). Various keywords used for retrieval of articles were Gallbladder, cancer Epidemiology, molecular genetics and bullion operators like AND, OR, NOT. Cross references were manually searched from various online search engines (http://www.ncbi.nlm.nih.gov/pubmed,https://scholar.google.co.in/, http://www.medline.com/home.jsp). Most of the articles published from 1982 to 2015 in peer reviewed journals have been included in this review.

Chromosomal structural analysis in carcinoma of the gallbladder

Background

The etiopathogenesis of gallbladder cancer is still unknown. Both environmental and patient factors have been incriminated in its cause. That it is found in pockets of epidemiological distribution raises an issue of genetic changes associated with it. The aim of this study was to find out the chromosomal changes in gallbladder cancer.

Methods

Lymphocyte cell culture was carried out on blood of gallbladder cancer patients to determine chromosomal banding abnormalities. Native PAGE was also evaluated to analyze lactate dehydrogenase (LDH), superoxide dismutase (SOD) and catalase enzyme activity from the same blood of gallbladder cancer patients.

Results

Out of 30 gallbladder cancer patients, 4 male showed breakage on the long arm of chromosome 1 while only one male patient showed the translocation from the long arm of chromosome 4 to the long arm of chromosome 6 in a male patient.

Conclusion

The aberrations found in our study may suggest underlying genetic predisposition for the development of gallbladder cancer. They can act as a marker for gallbladder cancer, which needs further study.

Two distinct pathways of p16 gene inactivation in gallbladder cancer

AIM: To examine the mechanism of inactivation of the p16 gene in gallbladder cancer, and to investigate p16 alterations and their correlation with clinicopathological features.

METHODS: Specimens were collected surgically from 51 patients with gallbladder cancer. We evaluated the status of protein expression, loss of heterozygosity (LOH), homozygous deletion and promoter hypermethylation using immunohistochemistry, microsatellite analysis, quantitative real-time polymerase chain reaction (PCR) and methylation-specific PCR, respectively. In addition, mutations were examined by direct DNA sequencing.

RESULTS: Homozygous deletions of the p16 gene exon2, LOH at 9p21-22, p16 promoter hypermethylation, and loss of p16 protein expression were detected in 26.0% (13/50), 56.9% (29/51), 72.5% (37/51) and 62.7% (32/51), respectively. No mutations were found. LOH at 9p21 correlated with the loss of p16 protein expression (P < 0.05). Homozygous deletion of the p16 gene, a combination LOH and promoter hypermethylation, and multiple LOH at 9p21 were significantly correlated with the loss of p16 protein expression (P < 0.05). LOH at 9p21 and promoter hypermethylation of the p16 gene were detected in 15.4% (2/13) and 92.3% (12/13) of the tumors with homozygous deletion of the p16 gene, respectively. P16 alterations were not associated with clinicopathological features.

CONCLUSION: Our results suggest that LOH and homozygous deletion may be two distinct pathways in the inactivation of the p16 gene. Homozygous deletion, a combination of LOH and promoter hypermethylation, and multiple LOH are major mechanisms of p16 inactivation in gallbladder cancer.

Allelic Loss in a Minimal Region on Chromosome 16q24 Is Associated with Vitreous Seeding of Retinoblastoma

In addition to RB1 gene mutations, retinoblastomas frequently show gains of 1q and 6p and losses of 16q. To identify suppressor genes on 16q, we analyzed 22 short tandem repeat loci in 58 patients with known RB1 mutations. A subset of tumors was also investigated by conventional and matrix comparative genomic hybridization. In 40 of 58 (69%) tumors, we found no loss of heterozygosity (LOH) at any 16q marker. LOH was detected in 18 of 58 (31%) tumors, including five with allelic imbalance at some markers. In one tumor LOH was only observed at 16q24. As the parental origin of allele loss was unbiased, an imprinted locus is unlikely to be involved. Analysis of gene expression by microarray hybridization and quantitative RT real-time PCR did not identify a candidate suppressor in 16q24. Cadherin 13 (CDH13), CBFA2T3, and WFDC1, which are candidate suppressors in other tumor entities with 16q24 loss, did not show loss of expression. In addition, mutation and methylation analysis showed no somatic alteration of CDH13. Results in all tumors with chromosome 16 alterations define a single minimal deleted region of 5.7 Mb in the telomeric part of 16q24 with the centromeric boundary defined by retention of heterozygosity for a single nucleotide variant in exon 10 of CDH13 (Mb 82.7). Interestingly, clinical presentation of tumors with and without 16q alterations was distinct. Specifically, almost all retinoblastomas with 16q24 loss showed diffuse intraocular seeding. This suggests that genetic alterations in the minimal deleted region are associated with impaired cell-to-cell adhesion.

K-ras, p53 mutations, and microsatellite instability (MSI) in gallbladder cancer

Despite the considerable progress in understanding the molecular pathology of carcinogenesis, the genetic mechanisms underlying the development and progression of gallbladder cancer (GC) are poorly understood. The survival of GC patients is generally poor. Therefore, it is very useful to define valuable prognostic factors. The most extensively studied oncogenes in gallbladder carcinogenesis are ras, commonly mutated in neoplasms of the gastrointestinal tract. K-ras oncogene is altered in a subset of gallbladder patients and mainly in those having anomalous junction of the pancreaticobiliary tract. Most of the studies of genetic abnormalities in GC have focused on p53 gene. p53 mutation/overexpression and/or LOH is present in more than 50% of gallbladder carcinomas, suggesting an important role in their pathogenesis. However, these results have not any predictive value yet. Moreover, the involvement of an alternative molecular pathway, that of microsatellite instability (MSI), is found in a limited group of GC patients. Additional research is necessary to establish its possible relation to defects of the mismatch repair (MMR) system and its proposed prognostic significance. Further elucidation of the molecular events specific to GC will help to identify novel molecular targets for the diagnosis and clinical management of the patients.

High-level microsatellite instability is not involved in gallbladder carcinogenesis

The molecular alterations involved in the pathogenesis of gallbladder cancer are not yet well defined. Our aim was to determine the microsatellite status of gallbladder carcinomas and its possible correlation with alterations in K-ras and p53 genes as well as the clinicopathological characteristics of these tumors. A group of 37 gallbladder carcinomas was analyzed for alterations in a proposed panel of mononucleotide and dinucleotide markers of microsatellite instability. Somatic frameshift mutations at repeated sequences in the coding regions of TGF-betaRII, Bax, hMSH3, hMSH6 were also examined. The findings were correlated with the presence of K-ras and p53 alterations, and tumors' clinicopathological features. Microsatellite instability and/or LOH was observed in 9 gallbladder carcinomas. Cases showing microsatellite instability displayed alterations only in dinucleotide markers and were classified as MSI-L carcinomas. A subset of gallbladder carcinomas is characterized by low-level instability, based on the analysis of the above mentioned panel of markers. The pathway of microsatellite instability seems to play a minor role in the pathogenesis of gallbladder cancer.

Gallbladder cancer: lessons from a rare tumour

Gallbladder cancer is a relatively rare form of malignancy about which our knowledge is scant. However, a unique combination of predisposing factors - including genetic predisposition, geographic distribution, female gender bias, chronic inflammation and congenital developmental abnormalities - makes this type of cancer unique and offers potential for understanding cancer pathogenesis in general. An understanding of how these risk factors contribute to the molecular basis of the disease is essential for understanding the origins of this unusual cancer.

Microsatellite instability and p53 expression in gallbladder carcinomas

We studied the MSI (microsatellite instability) status and p53 expression in a series of 71 gallbladder cancers (GCs) of different histologic type. All neoplasms were examined combining a microsatellite analysis at mononucleotide locus BAT-26 and an immunohistochemical study for hMSH2, hMLH1, and p53 proteins and markers of gastric and intestinal differentiation. All the 71 GCs were MSS (microsatellite stable). The p53 protein was found in 100% of undifferentiated GCs, 67% of conventional gallbladder adenocarcinomas, 50% of mucinous adenocarcinomas, and 20% GCs with squamous differentiation. All 71 MSS tumors showed presence of immunohistochemical expression of both hMLH1 and hMSH2 gene products. We concluded that microsatellite instability does not play a role in the developing of GC while p53 seems to be the most important alteration found in a large proportion of these cancers, with the only exception of mucinous and squamous gallbladder carcinomas.