Frequent Loss of Heterozygosity but Rare Microsatellite Instability in Oesophageal Cancer in Japanese and Chinese Patients

Epstein-Barr virus and mismatch repair deficiency status differ between oesophageal and gastric cancer: A large multi-centre study

BACKGROUND

Oesophageal (OeC) and gastric (GC) cancer patients are treated with similar multimodal therapy and have poor survival. There remains an urgent clinical need to identify biomarkers to individualise patient management and improve outcomes. Therapy with immune checkpoint inhibitors has shown promising results in other cancers. Proposed biomarkers to predict potential response to immune checkpoint inhibitors include DNA mismatch repair (MMR) and/or Epstein-Barr virus (EBV) status. The aim of this study was to establish and compare EBV status and MMR status in large multi-centre series of OeC and GC.

METHODS

EBV was assessed by EBV-encoded RNA (EBER) in situ hybridisation and MMR protein expression by immunohistochemistry (IHC) in 988 OeC and 1213 GC from multiple centres. In a subset of OeC, microsatellite instability (MSI) was tested in parallel with MMR IHC.

RESULTS

Frequency of MMR deficiency (MMRdef) and MSI was low in OeC (0.8% and 0.6%, respectively) compared with GC (10.3%). None of the OeCs were EBER positive in contrast to 4.8% EBER positive GC. EBV positive GC patients were younger (p = 0.01), more often male (p = 0.001) and had a better overall survival (p = 0.012). MMRdef GC patients were older (p = 0.001) and showed more often intestinal-type histology (p = 0.022).

CONCLUSIONS

This is the largest study to date indicating that EBV and MMRdef do not play a role in OeC carcinogenesis in contrast to GC. The potential clinical usefulness of determining MMRdef/EBV status to screen patients for eligibility for immune-targeting therapy differs between OeC and GC patients.

A specific mode of microsatellite instability is a crucial biomarker in adult T-cell leukaemia/lymphoma patients

Purpose

Microsatellite instability (MSI) has been a long-standing biomarker candidate for drug resistance in tumour cells. Despite numerous clinical studies, the data in the literature are not conclusive. The complexity of the MSI phenomenon in some malignancies may, at least partly, account for the discrepancy. In addition, methodological problems are also pointed out in the assay techniques. We previously established a unique fluorescent technique in which the major methodological problems in conventional assays are overcome. Application of this technique has revealed two distinct modes of microsatellite alterations, i.e. Type A and Type B. More importantly, we demonstrated that Type A MSI is the direct consequence of defective DNA mismatch repair (MMR) that causes cellular resistance against antineoplastic agents.

Method

We first applied this technique to adult T-cell leukaemia/lymphoma (ATLL).

Results

The MSI phenomenon was indeed observed in ATLLs (4/20, 20%). Intriguingly, the observed microsatellite alterations were invariably Type A, which implies that the tumours were MMR-defective. Indeed, clinical outcomes of patients with these MSI⁺ tumours were significantly worse. Furthermore, multivariate analysis revealed that Type A MSI is an independent prognostic factor.

Conclusion

These observations strongly suggest the possibility of Type A MSI as a prognostic and potentially predictive biomarker in ATLL.

Genetic features of metachronous esophageal cancer developed in Hodgkin's lymphoma or breast cancer long-term survivors: an exploratory study

Background

Development of novel therapeutic drugs and regimens for cancer treatment has led to improvements in patient long-term survival. This success has, however, been accompanied by the increased occurrence of second primary cancers. Indeed, patients who received regional radiotherapy for Hodgkin’s Lymphoma (HL) or breast cancer may develop, many years later, a solid metachronous tumor in the irradiated field. Despite extensive epidemiological studies, little information is available on the genetic changes involved in the pathogenesis of these solid therapy-related neoplasms.

Methods

Using microsatellite markers located in 7 chromosomal regions frequently deleted in sporadic esophageal cancer, we investigated loss of heterozygosity (LOH) and microsatellite instability (MSI) in 46 paired (normal and tumor) samples. Twenty samples were of esophageal carcinoma developed in HL or breast cancer long-term survivors: 14 squamous cell carcinomas (ESCC) and 6 adenocarcinomas (EADC), while 26 samples, used as control, were of sporadic esophageal cancer (15 ESCC and 11 EADC).

Results

We found that, though the overall LOH frequency at the studied chromosomal regions was similar among metachronous and sporadic tumors, the latter exhibited a statistically different higher LOH frequency at 17q21.31 (p = 0.018). By stratifying for tumor histotype we observed that LOH at 3p24.1, 5q11.2 and 9p21.3 were more frequent in ESCC than in EADC suggesting a different role of the genetic determinants located nearby these regions in the development of the two esophageal cancer histotypes.

Conclusions

Altogether, our results strengthen the genetic diversity among ESCC and EADC whether they occurred spontaneously or after therapeutic treatments. The presence of histotype-specific alterations in esophageal carcinoma arisen in HL or breast cancer long-term survivors suggests that their transformation process, though the putative different etiological origin, may retrace sporadic ESCC and EADC carcinogenesis.

Loss of p53 in esophageal squamous cell carcinoma and the correlation with survival: analyses of gene mutations, protein expression, and loss of heterozygosity in Japanese patients

BACKGROUND

A high frequency of p53 protein expression or gene mutation has been reported in the early stages of esophageal squamous cell carcinoma (ESCC), and thus loss of p53 function is thought to be very important in esophageal carcinogenesis. However, there is controversy surrounding the correlation between p53 dysfunction and ESCC tumor progression. The complexity arises from the different modalities, such as mutation analysis, immunohistochemistry, and the detection of loss of heterozygosity (LOH) at the p53 genomic locus.

METHODS

In this study, we comprehensively analyzed p53 gene mutation, p53 protein expression, and LOH at 17p13 in 94 surgically resected Japanese cases of ESCC.

RESULTS

The frequency of p53 gene mutation was 60.6%. The rate of positive p53 protein expression was 56.4%. The frequency of LOH at 17p13 was 67.5%. There was a statistically significant correlation between the presence of a gene mutation and LOH, whereas, there was no significant correlation between gene mutation and protein expression.

CONCLUSIONS

Despite the importance of loss of p53 function in esophageal carcinogenesis, none of the examined parameters, either singly or combined, correlated with overall survival. Taken together, p53 function is a primary target for esophageal carcinogenesis but there is no apparent correlation with the malignant phenotype in ESCC.

Copy-neutral loss of heterozygosity at the p53 locus in carcinogenesis of esophageal squamous cell carcinomas associated with p53 mutations

PURPOSE

LOH at the p53 locus has been reported to be associated with esophageal squamous cell carcinogenesis. The aim of this study is to identify potential mechanisms resulting in LOH around the p53 locus in its carcinogenesis.

EXPERIMENTAL DESIGN

We investigated 10 esophageal cancer cell lines and 91 surgically resected specimens, examining them for LOH at the p53 locus on chromosome 17. We examined the p53 gene by using microsatellite analysis, comparative genomic hybridization (CGH), FISH, and single-nucleotide polymorphism-CGH (SNP-CGH).

RESULTS

In an analysis of specimens by microsatellite markers, a close positive correlation was found between p53 mutations and LOH at the p53 locus (P < 0.01). Although four cell lines were found to be homozygous for p53 mutations, LOH at the p53 locus was not detected by CGH. Among two p53 mutant cancer cell lines and five p53 mutant/LOH cancer specimens analyzed by FISH, both the cell lines and four of the specimens exhibited no obvious copy number loss at the p53 locus. SNP-CGH analysis, which allows both determination of DNA copy number and detection of copy-neutral LOH, showed that LOHs without copy number change were caused by whole or large chromosomal alteration.

CONCLUSIONS

LOH without copy number change at the p53 locus was observed in p53 mutant esophageal squamous cell carcinomas. Our data suggest that copy-neutral LOH occurring as a result of chromosomal instability might be the major mechanism for inactivation of the intact allele in esophageal squamous cell carcinogenesis associated with p53 mutation.

High incidence and frequency of LOH are associated with aggressive features of high-grade HER2 and triple-negative breast cancers

BACKGROUND

Basal-like and HER2-overexpressing breast carcinomas are histologically undifferentiated, high-grade tumors with a high proliferation rate and associated with a poor outcome. Most basal-like tumors lack the expression of ER, PR, and HER2 (triple-negative; TN). Loss of heterozygosity (LOH) is thought to reflect random chromosomal instability, and recent studies have shown that DNA-copy number alterations or LOH occur with a high frequency in basal-like and HER2-amplified tumors.

METHODS

The levels and patterns of LOH were analyzed by the microsatellite alteration analysis using fluorescence-labeled primers and an automated DNA sequencer at 5 randomly selected loci in 246 Japanese primary breast cancers. Associations between the level of LOH and breast cancer subtypes and tumor aggressiveness were investigated.

RESULTS

The incidence and frequency of LOH was significantly higher in HER2 (56.3, 26.7%) and TN groups (44.4, 27.1%) than in luminal A (ER-positive and/or PR-positive and HER2-negative) groups (32.0, 12.2%). The incidence and frequency of LOH increased as nuclear grade was elevated. There were significantly more grade 3 tumors in the HER2 (80.0%) and TN (68.2%) subgroups (p < 0.0001). Even in HER2 and TN cases, the incidence and frequency of LOH was significantly higher in nuclear grade 3 cases than in grade 1 or 2 cases. Relapse-free survival of patients with LOH was significantly shorter than for those without LOH. In addition, the survival time was shorter as the frequency of LOH elevated. The incidence of LOH was an independent prognostic factor for relapse-free survival by multivariate analysis.

CONCLUSION

High incidence and frequency of LOH, which indicate increased genetic instability, were found to be associated with the aggressive features of high-grade HER2 and TN breast cancers.

DNA repair dysfunction in gastrointestinal tract cancers

The DNA repair system surveys the genome, which is always suffering from exposure to both exogenous as well as endogenous mutagens, to maintain the genetic information. The fact that the basis of this DNA repair system is highly conserved, from prokaryote to mammalian cells, suggests the importance of precise genome maintenance mechanisms for organisms. In the past 15 years, considerable progress has been made in understanding how repair processes interact and how disruptions of these mechanisms lead to the accumulation of mutations and carcinogenesis. In 1993, two groups reported that DNA mismatch repair could be associated with hereditary non-polyposis colorectal cancer, indicating a connection between faulty DNA repair function and cancer. More recently, an inherited disorder of DNA glycosylase, which removes mutagenic oxidized base from DNA, has been reported in individuals with a predisposition to multiple colorectal adenomas and carcinomas. This is the first report that directly indicates the role of the repair of oxidative DNA in human inherited cancer. Studies from gene knockout mice have elucidated the principal role of these repair systems in the process of carcinogenesis. Moreover, clinical samples derived from cancer patients have shown the direct involvement. This review focuses on the function of DNA mismatch repair and oxidative DNA/nucleotide repair among various DNA repair systems in cells, both of which are essentially involved in the carcinogenesis of gastrointestinal tract cancer.

p53 gene mutations in esophageal squamous cell carcinoma and their relevance to etiology and pathogenesis: results in Japan and comparisons with other countries

Esophageal squamous cell carcinoma is a form of cancer that has varying incidence rates among different countries, distinct geographic areas and different ethnic groups. According to previous reports, p53 gene mutations have been identified in 20-80% of these tumors, and these mutations have occurred at an early stage. These findings suggest that such mutations play an important role in esophageal carcinogenesis, and highlight the importance of mutagens, which cause sequence alterations in the p53 gene. In order to clarify the environmental factors and the molecular mechanisms that may be responsible for the occurrence and prevention of a specific mutation in the process of esophageal carcinogenesis, we analyzed p53 gene mutations in 95 samples of esophageal squamous cell carcinoma. We further reviewed published reports investigating the frequency of p53 gene mutations in esophageal cancer from high-risk areas to normal-risk areas and compared these findings to our results in Japan. The frequency of p53 gene mutations in Japanese esophageal cancer is 47.4% and there are three prominent features: (1) a predominance of transversions, in particular the G:C to T:A transversion; (2) a relatively low frequency of transitions; and (3) a relatively high percentage of frameshift mutations. These results indicate the possible importance of the benzo[a]pyrene metabolite and oxidative DNA damage in esophageal carcinogenesis and scarcely correlate with DNA replication errors or alkylation in comparison to other gastrointestinal cancers. In addition, we observed a peculiar sequence of frameshift mutations. Taken together, these data suggest that this tumor suppressor gene plays a critical role in the multistep carcinogenesis process for esophageal squamous cell cancer.

Early genetic instability of both epithelial and stromal cells in esophageal squamous cell carcinomas, contrasted with Barrett's adenocarcinomas

BACKGROUND

We have shown previously that stromal genetic alteration may make a greater contribution to early genesis of ulcerative colitis-associated tumors than sporadic colon cancers. We assessed whether similar differences in genetic alteration might exist between squamous cell carcinomas (SCCs) and Barrett's adenocarcinomas (BACs) of the esophagus.

METHODS

We investigated epithelial and stromal genetic instability with five National Cancer Institute standard (NCI), four chromosome 17 (Chr. 17), and six tumor suppressor gene (TSG) microsatellite markers in 26 SCC and 12 BAC cases and in 11 normal controls, using a novel combination of microdissection, polymerase chain reaction, and GeneScan.

RESULTS

Frequency of epithelial loss of heterozygosity (LOH) increased in the order background mucosa, to precursor lesions, to tumors with both types of carcinoma, especially for the Chr. 17 and TSG markers, while stromal LOH was relatively high but consistent from background mucosa to carcinoma. Epithelial LOH of D17S796 demonstrated a significantly higher frequency in SCCs than in BACs, without significant variation in p53 overexpression. The frequency of microsatellite instability (MSI) showed constant high levels in both epithelium and stroma of background, dysplasia, and carcinomas in the SCC series, and rather low frequencies in the BAC series. Although epithelial hMLH1 and hMSH2 expression decreased with tumor progression, no correlation was found with the individual MSI status.

CONCLUSIONS

Although epithelial LOH exists similarly in both lesion types, whereas epithelial and stromal MSI may occur in a relatively early phase of SCC development, stromal MSI is rare in BACs, strongly suggesting differences in tumorigenesis between the two types.

Coexistence of the loss of heterozygosity at the PTEN locus and HER2 overexpression enhances the Akt activity thus leading to a negative progesterone receptor expression in breast carcinoma

Serine/threonine kinase Akt/PKB is known to regulate divergent cellular processes, including apoptosis, proliferation, differentiation, and metabolism. Akt is activated by a variety of stimuli, through such growth factor receptors as HER2, in phosphoinositide-3-OH kinase (PI3K)-dependent manner. A loss of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) function also activates Akt. It has recently been shown that Akt activation is associated with a worse outcome among endocrine treated breast cancer patients and that it also inhibits the progesterone receptor (PR) expression via the PI3K/Akt pathway in breast cancer cells. Therefore, the PI3K/Akt signaling pathway has recently attracted considerable attention as a new target for effective therapeutic strategies. In the present study, we investigated the relationship between Akt activation and either HER2 overexpression or PTEN gene alteration, as well as the PR expression. We analyzed the incidence of LOH at the PTEN locus in 138 breast cancer patients, using our new system for microsatellite analysis, called high-resolution fluorescent microsatellite analysis (HRFMA). We showed Akt activation to significantly correlate with HER2 overexpression or LOH at the PTEN gene locus while inversely correlating with the PR expression. In addition, when LOH at the PTEN gene locus and HER2 overexpression occurred simultaneously, the incidence of Akt activation and reduced PR expression was significant. The association between Akt activation and PR negative expression was observed even in the ER-positive cases. Our results suggest that simultaneous PTEN LOH and HER2 overexpression enhances Akt activation and may thus lead to a negative PR expression.

Microsatellite instability in gastrointestinal tract cancers: a brief update

Microsatellite instability (MSI) was initially reported in colorectal cancer and, particularly, in hereditary nonpolyposis colorectal cancer (HNPCC). Since mutations in the genes functioning in DNA mismatch repair (MMR) were found in HNPCC kindred, this phenotype has been connected to a deficiency in MMR. The MSI(+) phenotype is associated with various human malignancies. As MSI(+) tumors appear to form a unique clinicopathological and molecular entity that is clearly distinct from that of classical colorectal tumors, which are accompanied by chromosomal instability (CIN), an exclusive pathway of tumorigenesis has been proposed in colorectal cancer. However, this scheme, comprising two mutually exclusive pathways, is now being reexamined, in light of a series of evidence accumulating in the literature, which relates to (a) distinction between high-level MSI (MSI-H) and low-level MSI (MSI-L), (b) heterogeneity in MSI-H, particularly in the sporadic and hereditary settings, (c) molecular mechanisms underlying the MSI(+) phenotypes, and (d) relationships between the MSI(+) and CIN phenotypes. Several molecular mechanisms may underlie repeat instability in eukaryotic cells. The relationship between MSI and defective MMR may be more complicated than has been suspected. The role of MMR deficiency in tumorigenesis in the digestive tract appears to be diverse and is not simple, even in the colorectum.