Molecular and prognostic heterogeneity of microsatellite-unstable colorectal cancer

Colorectal cancers (CRCs) with a high level of microsatellite instability (MSI-H) are clinicopathologically distinct tumors characterized by predominance in females, proximal colonic localization, poor differentiation, mucinous histology, tumor-infiltrating lymphocytes, a Crohn’s-like lymphoid reaction and a favorable prognosis. In terms of their molecular features, MSI-H CRCs are heterogeneous tumors associated with various genetic and epigenetic alterations, including DNA mismatch repair deficiency, target microsatellite mutations, BRAF mutations, a CpG island methylator phenotype-high (CIMP-H) status, and a low level of genomic hypomethylation. The molecular heterogeneity of MSI-H CRCs also depends on ethnic differences; for example, in Eastern Asian countries, relatively low frequencies of CIMP-H and BRAF mutations have been observed in MSI-H CRCs compared to Western countries. Although the prognostic features of MSI-H CRCs include a favorable survival of patients and low benefit of adjuvant chemotherapy, there may be prognostic differences based on the molecular heterogeneity of MSI-H CRCs. Here, we have reviewed and discussed the molecular and prognostic features of MSI-H CRCs, as well as several putative prognostic or predictive molecular markers, including HSP110 expression, beta2-microglobulin mutations, myosin 1a expression, CDX2/CK20 expression, SMAD4 expression, CIMP status and LINE-1 methylation levels.

Use of blood-based biomarkers for early diagnosis and surveillance of colorectal cancer

Early screening for colorectal cancer (CRC) holds the key to combat and control the increasing global burden of CRC morbidity and mortality. However, the current available screening modalities are severely inadequate because of their high cost and cumbersome preparatory procedures that ultimately lead to a low participation rate. People simply do not like to have colonoscopies. It would be ideal, therefore, to develop an alternative modality based on blood biomarkers as the first line screening test. This will allow for the differentiation of the general population from high risk individuals. Colonoscopy would then become the secondary test, to further screen the high risk segment of the population. This will encourage participation and therefore help to reach the goal of early detection and thereby reduce the anticipated increasing global CRC incidence rate. A blood-based screening test is an appealing alternative as it is non-invasive and poses minimal risk to patients. It is easy to perform, can be repeated at shorter intervals, and therefore would likely lead to a much higher participation rate. This review surveys various blood-based test strategies currently under investigation, discusses the potency of what is available, and assesses how new technology may contribute to future test design.

An updated review of gastric cancer in the next-generation sequencing era: Insights from bench to bedside and vice versa

Gastric cancer (GC) is one of the most common malignancies and remains the second leading cause of cancer-related death worldwide. There is an increasing understanding of the roles that genetic and epigenetic alterations play in GCs. Recent studies using next-generation sequencing (NGS) have revealed a number of potential cancer-driving genes in GC. Whole-exome sequencing of GC has identified recurrent somatic mutations in the chromatin remodeling gene ARID1A and alterations in the cell adhesion gene FAT4, a member of the cadherin gene family. Mutations in chromatin remodeling genes (ARID1A, MLL3 and MLL) have been found in 47% of GCs. Whole-genome sequencing and whole-transcriptome sequencing analyses have also discovered novel alterations in GC. Recent studies of cancer epigenetics have revealed widespread alterations in genes involved in the epigenetic machinery, such as DNA methylation, histone modifications, nucleosome positioning, noncoding RNAs and microRNAs. Recent advances in molecular research on GC have resulted in the introduction of new diagnostic and therapeutic strategies into clinical settings. The anti-human epidermal growth receptor 2 (HER2) antibody trastuzumab has led to an era of personalized therapy in GC. In addition, ramucirumab, a monoclonal antibody targeting vascular endothelial growth factor receptor (VEGFR)-2, is the first biological treatment that showed survival benefits as a single-agent therapy in patients with advanced GC who progressed after first-line chemotherapy. Using NGS to systematically identify gene alterations in GC is a promising approach with remarkable potential for investigating the pathogenesis of GC and identifying novel therapeutic targets, as well as useful biomarkers. In this review, we will summarize the recent advances in the understanding of the molecular pathogenesis of GC, focusing on the potential use of these genetic and epigenetic alterations as diagnostic biomarkers and novel therapeutic targets.

A dual-fluorescent reporter facilitates identification of thiol compounds that suppress microsatellite instability induced by oxidative stress

The DNA mismatch-repair (MMR) system corrects replicative errors and minimizes mutations that occur at a high rate in microsatellites. Patients with chronic inflammation or inflammation-associated cancer display microsatellite instability (MSI), indicating a possible MMR inactivation. In fact, H2O2-generated oxidative stress inactivates the MMR function and increases mutation accumulation in a reporter microsatellite. However, it remains unclear whether MSI induced by oxidative stress is preventable because of the lack of a sufficiently sensitive detection assay. Here, we developed and characterized a dual-fluorescent system, utilizing DsRed harboring the (CA)13 microsatellite as a reporter and GFP for normalization, in near-isogenic human colorectal cancer cell lines. Via flow cytometry, this reporter sensitively detected H2O2-generated oxidative microsatellite mutations in a dose-dependent manner. The reporter further revealed that glutathione or N-acetylcysteine was better than aspirin and ascorbic acid for suppressing oxidative microsatellite mutations. These two thiol compounds also partially suppressed oxidative frameshift mutations in the coding microsatellites of the hMSH6 and CHK1 genes based on a fluoresceinated PCR-based assay. MSI suppression by N-acetylcysteine appears to be mediated through reduction of oxidative frameshift mutations in the coding microsatellite of hMSH6 and protection of hMSH6 and other MMR protein levels from being decreased by H2O2. Our findings suggest a linkage between oxidative damage, MMR deficiency, and MSI. The two thiol compounds are potentially valuable for preventing inflammation-associated MSI. The dual-fluorescent reporter with improved features will facilitate identification of additional compounds that modulate MSI, which is relevant to cancer initiation and progression.

Serrated pathway in colorectal carcinogenesis

Serrated adenocarcinoma is a recently described subset of colorectal cancer (CRC), which account for about 10% of all CRCs and follows an alternative pathway in which serrated polyps replace the traditional adenoma as the precursor lesion to CRC. Serrated polyps form a heterogeneous group of colorectal lesions that includes hyperplastic polyps (HPs), sessile serrated adenoma (SSA), traditional serrated adenoma (TSA) and mixed polyps. HPs are the most common serrated polyp followed by SSA and TSA. This distinct histogenesis is believed to have a major influence in prevention strategies, patient prognosis and therapeutic impact. Genetically, serrated polyps exhibited also a distinct pattern, with KRAS and BRAF having an important contribution to its development. Two other molecular changes that have been implicated in the serrated pathway include microsatellite instability and the CpG island methylator phenotype. In the present review we will address the current knowledge of serrated polyps, clinical pathological features and will update the most recent findings of its molecular pathways. The understanding of their biology and malignancy potential is imperative to implement a surveillance approach in order to prevent colorectal cancer development.

Is microsatellite instability really a good prognostic factor of colorectal cancer?

PURPOSE

The aim of this study was to investigate the clinicopathologic features of and the prognosis for colorectal cancers (CRCs) with microsatellite instabilities (MSIs).

METHODS

Between 2006 and 2009, genotyping was performed on 245 patients with stage II/III CRCs to establish the MSI status. The clinicopathologic differences and the prognostic value of MSI were analyzed. The median follow-up period was 38 months (range, 7-68 months).

RESULTS

Of the total 245 patients, 20 (8.2%) had MSI-high (H) and 225 (91.8%) had MSI-low (L) or stable (S) CRCs. Adjuvant chemotherapies were performed on 101 stage II (87.8%) and 107 stage III patients (82.3%). Patients with MSI-H CRCs more frequently had a family history of colon cancer (10% vs. 2.7%, P = 0.003), more frequently had a cancer located at the proximal colon (90.0% vs. 19.1%, P < 0.0001), and more often showed a mucinous phenotype or poor differentiation (35.0% vs. 7.1%, P = 0.001). Despite less frequent lymph node metastasis (25% vs. 55.6%, P = 0.01), the number of retrieved lymph nodes was higher (26.3 ± 13.1 vs. 20.7 ± 1.2, P = 0.04) in the MSI-H group. The overall survival and the disease-free survival (DFS) did not differ with respect to MSI status. However, in the stage II subgroup, the DFS for patients with MSI-H CRCs was significantly worse (72.2% vs. 90.7%, P = 0.03). The multivariate analysis performed on this subgroup revealed that MSI-H was an independent poor prognostic factor (adjusted hazard ratio, 4.0; 95% confidence interval, 1.0-15.6, P = 0.046).

CONCLUSION

MSI-H CRCs had distinct clinicopathologic features, and MSI-H was an independent poor prognostic factor in stage II CRCs. Considering the majority of stage II patients were administrated adjuvant chemotherapy, the efficacy of adjuvant chemotherapy for treating MSI CRCs might be different from that for treating MSI-L/S tumors.

ARID1A/BAF250a as a prognostic marker for gastric carcinoma: a study of 2 cohorts

ARID1A/BAF250a has been recently implicated as a tumor suppressor in gastric cancer. We sought to clarify the clinical significance of BAF250a/ARID1A in relation to other clinical parameters and relevant biomarkers in gastric carcinoma. Cases from 2 separate cohorts of patients with gastric carcinoma from Vancouver (n = 173) and Toronto (n = 80) were selected for the construction of tissue microarrays, which were used to assess the immunohistochemical status of BAF250a (anti-ARID1A), mismatch repair proteins and p53, as well as in situ hybridization for HER2 amplification and Epstein-Barr virus infection. The Toronto cohort contained a higher proportion of early stage cases (P = .019) and a smaller proportion of cases from the proximal stomach (P < .001). Overall, immunohistochemical loss of BAF250a was observed in 22.5% of gastric adenocarcinomas from the Vancouver group and 20% from Toronto. In both cohorts, loss of BAF250a was positively associated with loss of mismatch repair protein expression (P < .0001 and P = .035, respectively). Loss of BAF250a expression was independently associated with poor overall survival in the Toronto cohort (P = .0015), whereas no significant association with survival was observed in the Vancouver cohort. BAF250a loss was not significantly associated with any additional clinical parameters in either cohort. HER2 amplification was confirmed as a negative prognostic factor in both cohorts. These findings suggest that ARID1A/BAF250a may be of prognostic significance in a subset of patients with early stage gastric cancer and that pathological assessment should increasingly use a multimarker approach.

p53-Dependent suppression of genome instability in germ cells

Radiation increases mutation frequencies at tandem repeat loci. Germline mutations in γ-ray-irradiated medaka fish (Oryzias latipes) were studied, focusing on the microsatellite loci. Mismatch-repair genes suppress microsatellite mutation by directly removing altered sequences at the nucleotide level, whereas the p53 gene suppresses genetic alterations by eliminating damaged cells. The contribution of these two defense mechanisms to radiation-induced microsatellite instability was addressed. The spontaneous mutation frequency was significantly higher in msh2(-/-) males than in wild-type fish, whereas there was no difference in the frequency of radiation-induced mutations between msh2(-/-) and wild-type fish. By contrast, irradiated p53(-/-) fish exhibited markedly increased mutation frequencies, whereas their spontaneous mutation frequency was the same as that of wild-type fish. In the spermatogonia of the testis, radiation induced a high level of apoptosis both in wild-type and msh2(-/-) fish, but negligible levels in p53(-/-) fish. The results demonstrate that the msh2 and p53 genes protect genome integrity against spontaneous and radiation-induced mutation by two different pathways: direct removal of mismatches and elimination of damaged cells.

Mosaic analysis and tumor induction in zebrafish by microsatellite instability-mediated stochastic gene expression

Mosaic analysis, in which two or more populations of cells with differing genotypes are studied in a single animal, is a powerful approach to study developmental mechanisms and gene function in vivo. Over recent years, several genetic methods have been developed to achieve mosaicism in zebrafish, but despite their advances, limitations remain and different approaches and further refinements are warranted. Here, we describe an alternative approach for creating somatic mosaicism in zebrafish that relies on the instability of microsatellite sequences during replication. We placed the coding sequences of various marker proteins downstream of a microsatellite and out-of-frame; in vivo frameshifting into the proper reading frame results in expression of the protein in random individual cells that are surrounded by wild-type cells. We optimized this approach for the binary Gal4-UAS expression system by generating a driver line and effector lines that stochastically express Gal4-VP16 or UAS:H2A-EGFP and self-maintaining UAS:H2A-EGFP-Kaloop, respectively. To demonstrate the utility of this system, we stochastically expressed a constitutively active form of the human oncogene H-RAS and show the occurrence of hyperpigmentation and sporadic tumors within 5 days. Our data demonstrate that inducing somatic mosaicism through microsatellite instability can be a valuable approach for mosaic analysis and tumor induction in Danio rerio.

Genetic and clinical determinants of constitutional mismatch repair deficiency syndrome: report from the constitutional mismatch repair deficiency consortium

BACKGROUND

Constitutional mismatch repair deficiency (CMMRD) is a devastating cancer predisposition syndrome for which data regarding clinical manifestations, molecular screening tools and management are limited.

METHODS

We established an international CMMRD consortium and collected comprehensive clinical and genetic data. Molecular diagnosis of tumour and germline biospecimens was performed. A surveillance protocol was developed and implemented.

RESULTS

Overall, 22/23 (96%) of children with CMMRD developed 40 different tumours. While childhood CMMRD related tumours were observed in all families, Lynch related tumours in adults were observed in only 2/14 families (p=0.0007). All children with CMMRD had café-au-lait spots and 11/14 came from consanguineous families. Brain tumours were the most common cancers reported (48%) followed by gastrointestinal (32%) and haematological malignancies (15%). Importantly, 12 (30%) of these were low grade and resectable cancers. Tumour immunohistochemistry was 100% sensitive and specific in diagnosing mismatch repair (MMR) deficiency of the corresponding gene while microsatellite instability was neither sensitive nor specific as a diagnostic tool (p<0.0001). Furthermore, screening of normal tissue by immunohistochemistry correlated with genetic confirmation of CMMRD. The surveillance protocol detected 39 lesions which included asymptomatic malignant gliomas and gastrointestinal carcinomas. All tumours were amenable to complete resection and all patients undergoing surveillance are alive.

DISCUSSION

CMMRD is a highly penetrant syndrome where family history of cancer may not be contributory. Screening tumours and normal tissues using immunohistochemistry for abnormal expression of MMR gene products may help in diagnosis and early implementation of surveillance for these children.

Colorectal cancer in inflammatory bowel disease: results of the 3rd ECCO pathogenesis scientific workshop (I)

Epidemiological studies demonstrate an increased risk of colorectal cancer in patients with inflammatory bowel disease (IBD). A detailed literature review was conducted on epidemiology, risk factors, pathophysiology, chemoprevention and outcomes of colorectal cancer (CRC) in IBD as part of the 3rd ECCO scientific pathogenesis workshop.

Relationship between hMLH1 methylation, microsatellite instability and gastric cancer

Gastric cancer is one of the most common malignant tumors, and its development is a very complicated process. Although great progress has been made in the understanding of gastric cancer, its exact mechanism is still unclear. The human mutL homolog 1 (hMLH1), a main member of the mismatch repair system, participates in mismatch repair during DNA replication, and plays an important role in maintaining genome stability. The reduction or loss of hMLH1 expression, which often shows as microsatellite instability (MSI), is closely related to the development, treatment and prognosis of gastric cancer, and the main reason is hMLH1 promoter methylation. In this paper, we will review the recent progress in understanding the relationship between hMLH1 methylation, MSI and development, treatment and prognosis of gastric cancer.

Molecular diagnostics in the neoplasms of small intestine and appendix

Adenocarcinoma of the small intestine is relatively rare in comparison to colorectal carcinoma. Adenocarcinoma of the small intestine arises through the adenoma-carcinoma sequence in the colon. However, adenocarcinomas arising in the background of inflammatory bowel disease develop through the dysplasia-carcinoma sequence. Most of the cases occur in the duodenum; however, adenocarcinoma occurring in association with Crohn disease is more common in the ileum.

Risk factors for double primary malignancies and their clinical implications in patients with sporadic gastric cancer

AIMS

We carried out a large scale study to identify the risk factors for double primary malignancy (DPM) development in gastric cancer patients and to evaluate the clinical implications for these patients.

METHODS

A total of 2593 patients who underwent gastrectomy for primary gastric cancer from January 2005 to November 2010 were reviewed with regard to DPM. We compared the clinicopathological characteristics, risk factors for developing DPM, and prognosis between the DPM+ group and the DPM- group.

RESULTS

Of the 2593 patients, 152 (5.9%) were diagnosed with DPM. The most common accompanying malignancies were colorectal, lung and thyroid. Multivariate analysis indicated that age (p = 0.016) and MSI status (p = 0.002) were associated with a higher frequency of DPM. 30.3% of patients were diagnosed with DPM within 1 year around perioperative period and 53.3% of patients had DPM detected during 5 years of post-operative follow up periods. Although there was no significant difference in overall survival between the DPM+ and DPM- group, DPM+ patients had a worse prognosis than DPM- patients in stage I gastric cancer.

CONCLUSIONS

Gastric cancer patients over the age of 60 or with a MSI-high status had an increased risk for developing DPM. Further, in stage I gastric cancer, the presence of DPM was associated with a worse prognosis. Therefore, careful pre- and postoperative surveillance is especially important in these patients.

Knowledge of and practice patterns for hereditary colorectal cancer syndromes in korean surgical residents

Purpose

Obtaining a detailed family history through detailed pedigree is essential in recognizing hereditary colorectal cancer (CRC) syndromes. This study was performed to assess the current knowledge and practice patterns of surgery residents regarding familial risk of CRC.

Methods

A questionnaire survey was performed to evaluate the knowledge and the level of recognition for analyses of family histories and hereditary CRC syndromes in 62 residents of the Department of Surgery, Seoul National University Hospital. The questionnaire consisted of 22 questions regarding practice patterns for, knowledge of, and resident education about hereditary CRC syndromes.

Results

Two-thirds of the residents answered that family history should be investigated at the first interview, but only 37% of them actually obtained pedigree detailed family history at the very beginning in actual clinical practice. Three-quarters of the residents answered that the quality of family history they obtained was poor. Most of them could diagnose hereditary nonpolyposis colorectal cancer and recommend an appropriate colonoscopy surveillance schedule; however, only 19% knew that cancer surveillance guidelines differed according to the family history. Most of our residents lacked knowledge of cancer genetics, such as causative genes, and diagnostic methods, including microsatellite instability test, and indicated a desire and need for more education regarding hereditary cancer and genetic testing during residency.

Conclusion

This study demonstrated that surgical residents' knowledge of hereditary cancer was not sufficient and that the quality of the family histories obtained in current practice has to be improved. More information regarding hereditary cancer should be considered in education programs for surgery residents.

Tissue identity testing of cancer by short tandem repeat polymorphism: pitfalls of interpretation in the presence of microsatellite instability

Tissue identity testing by short tandem repeat (STR) polymorphism offers discriminating power in resolving tissue mix-up or contamination. However, one caveat is the presence of microsatellite unstable tumors, in which genetic alterations may drastically change the STR wild-type polymorphism leading to unexpected allelic discordance. We examined how tissue identity testing results can be altered by the presence of microsatellite instability (MSI). Eleven cases of MSI-unstable (9 intestinal and 2 endometrial adenocarcinomas) and 10 cases of MSI-stable tumors (all colorectal adenocarcinomas) were included. All had been previously tested by polymerase chain reaction testing at 5 National Cancer Institute (NCI) recommended MSI loci and/or immunohistochemistry for DNA mismatch repair proteins (MLH1, MSH2, MSH6, and PMS2). Tissue identity testing targeting 15 STR loci was performed using AmpF/STR Identifiler Amplification. Ten of 11 MSI-unstable tumors demonstrated novel alleles at 5 to 12 STR loci per case and frequently with 3 or more allelic peaks. However, all affected loci showed identifiable germline allele(s) in MSI-high tumors. A wild-type allelic profile was seen in 7 of 10 MSI-stable tumors. In the remaining 3 cases, isolated novel alleles were present at a unique single locus in addition to germline alleles. Loss of heterozygosity was observed frequently in both MSI-stable (6/11 cases) and MSI-unstable tumors (8/10 cases). In conclusion, MSI may significantly alter the wild-type allelic polymorphism, leading to potential interpretation errors of STR genotyping. Careful examination of the STR allelic pattern, high index of suspicion, and follow-up MSI testing are crucial to avoid erroneous conclusions and subsequent clinical and legal consequences.

Hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome, is a class of autosomal dominant genetic disease. Main clinical characteristics of HNPCC include early onset age, more common in the right colon, and concomitant with simultaneous or metachronous extracolonic cancers, including endometrial cancer, stomach cancer, and ovarian cancer. However, the prognosis of HNPCC is better than sporadic colorectal cancer. Screening and intervention for HNPCC among high-risk pedigree population can effectively reduce the cancer incidence and mortality. In this article we will review the pathogenesis, epidemiology, diagnosis, screening, prevention and treatment of HNPCC.

High-stage urachal adenocarcinoma can be associated with microsatellite instability and KRAS mutations

Urachal adenocarcinoma (UAC) is a rare tumor of the urinary bladder, which can show intestinal, mucinous, and signet ring cell histology. The morphology is similar to that of colorectal adenocarcinoma (CAC). Microsatellite instability (MSI), KRAS, and BRAF have been more extensively studied in CAC. What is not known is whether UAC in its morphologic similarity to CAC could show immunohistochemical features of MSI along with KRAS- and BRAF-activating mutations. A retrospective review of institutional archives for UAC cases found 7 cases, all of which were high stage. Most (6/7) of our UAC cases showed evidence of MSI or mutations of KRAS. No cases showed a BRAF mutation at codon 600. Of the cases that demonstrated MSI, 1 showed mutS homolog 2 and mutS homolog 6 loss, and 2 showed PMS2 (postmeiotic segregation increased 2) loss. Of the remaining 4 cases, 3 showed KRAS mutations at codon 12. Our UAC series showed mutual exclusivity of MSI and KRAS mutations. Furthermore, our UAC cases with KRAS mutations showed markedly better overall survival (mean, 101.7 versus 6.5 months; P = .035). Thus, our study justifies ancillary testing for MSI and KRAS in UAC, particularly when there is high-stage and mucinous histology, but a larger multi-institutional accruement of UAC cases is necessary to further validate our novel findings.

Poorly differentiated colorectal cancers: correlation of microsatellite instability with clinicopathologic features and survival

OBJECTIVES

To evaluate the association of microsatellite instability (MSI) with clinicopathologic features and oncologic outcomes in patients with poorly differentiated colorectal cancer (PD).

METHODS

Study patients were divided into well-differentiated colorectal cancer (WD) and PD, which were compared according to histologic differentiation and MSI status.

RESULTS

Among 1,941 patients, PD was more frequent among microsatellite-unstable tumors (23.6%) than among microsatellite-stable (MSS) tumors (4.2%, P < .001). Patients with PD had worse 4-year overall survival rates than patients with WD (78.6% vs 88.2%, P = 0.010). Compared with MSS-PD tumors, MSI-PD tumors were characterized by right-colon predilection, larger size, and infrequent lymph node metastasis (P < .001 to P = .007).

CONCLUSIONS

The clinicopathologic characteristics of PD were closely associated with those of MSI. The outcomes of MSI-PD tumors were better than those of MSS-PD tumors, but this finding did not reach statistical significance.

Distinct molecular features of colorectal cancer in Ghana

OBJECTIVES

While colorectal cancer (CRC) is common, its incidence significantly varies around the globe. The incidence of CRC in West Africa is relatively low, but it has a distinctive clinical pattern and its molecular characteristics have not been studied. This study is one of the first attempts to analyze molecular, genetic, and pathological characteristics of colorectal cancer in Ghana.

METHODS

DNA was extracted from microdissected tumor and adjacent normal tissue of 90 paraffin blocks of CRC cases (1997-2007) collected at the University of Ghana. Microsatellite instability (MSI) was determined using fragment analysis of ten microsatellite markers. We analyzed expression of mismatch repair (MMR) proteins by immunohistochemistry and sequenced exons 2 and 3 of KRAS and exon 15 of BRAF.

RESULTS

MSI analysis showed 41% (29/70) MSI-High, 20% (14/70) MSI-Low, and 39% (27/70) microsatellite-stable (MSS) tumors. Sequencing of KRAS exons 2 and 3 identified activating mutations in 32% (24/75) of tumors, and sequencing of BRAF exon 15, the location of the common activating mutation (V600), did not show mutations at codons 599 and 600 in 88 tumors.

CONCLUSIONS

Our study found a high frequency of MSI-High colorectal tumors (41%) in Ghana. While the frequency of KRAS mutations is comparable with other populations, absence of BRAF mutations is intriguing and would require further analysis of the molecular epidemiology of CRC in West Africa.

Endometrial cancer and a family history of cancer

OBJECTIVE

Lynch Syndrome (LS), an inherited genetic syndrome, predisposes to cancers such as colorectal and endometrial. However, the risk for endometrial cancer (EC) in women not affected by LS, but with a family history of cancer, is currently unknown. We examined the association between a family history of cancer and the risk for EC in non-LS patients.

METHODS

This population-based case-control study included 519 EC cases and 1015 age-matched controls and took place in Alberta, Canada between 2002 and 2006. Information about risk factors, including family history of cancer in first and second degree relatives, was ascertained via in-person interviews. Microsatellite instability (MSI) status of tumor tissue was assessed to determine involvement of DNA mismatch repair (MMR) genes.

RESULTS

A first or second degree family history of uterine cancer was modestly associated with the risk for overall EC [odds ratio (OR), 1.3; 95% confidence interval (CI), 0.9, 1.9], and the risks were similar for MSI+cancer (OR=1.5, 95%CI=0.7, 3.3) and MSI- cancer (OR=1.3, 95%CI=0.8, 2.4). Although consistent, these associations were modest and not significant. In contrast, the risk for MSI+cancer was elevated with a reported family history of colorectal cancer (OR=1.4, 95%CI=1.0, 2.2), but not for MSI- cancer.

CONCLUSIONS

A family history of uterine cancer may be modestly associated with EC risk in non-LS patients regardless of MSI status, suggesting that risk was not related to inherited defects in the MMR gene pathway. These results provide preliminary support for an EC-specific genetic syndrome.

BRAF V600E mutation analysis simplifies the testing algorithm for Lynch syndrome

OBJECTIVES

To evaluate our experience of adding reflex BRAF mutation analysis following mismatch repair (MMR) protein staining in the test algorithm for Lynch syndrome (LS), the most common inherited predisposition to colorectal cancer (CRC).

METHODS

Since January 1, 2009, BRAF V600E mutation analysis has been performed at our institution for all newly diagnosed CRCs with absent MLH1 and PMS2 proteins.

RESULTS

Ninety (22%) of 412 patients with CRC had at least 1 MMR absent (65 had MLH1 and PMS2 absent and 25 had other stain(s) absent). BRAF mutation was found in 36 (55%) of 65. Fifty-four (13%) of 412 patients required follow-up after addition of BRAF analysis compared with 90 who would have required follow-up without BRAF analysis.

CONCLUSIONS

The addition of reflex BRAF mutation testing in CRCs with absent MLH1 and PMS2 reduced the number of patient contacts by 40% and simplified the genetic testing for LS, leading to cost and time savings.

Underexpression of LATS1 TSG in colorectal cancer is associated with promoter hypermethylation

AIM

To investigate large tumor suppressor 1 (LATS1) expression, promoter hypermethylation, and microsatellite instability in colorectal cancer (CRC).

METHODS

RNA was isolated from tumor tissue of 142 CRC patients and 40 colon mucosal biopsies of healthy controls. After reverse transcription, quantitative polymerase chain reaction (PCR) was performed, and LATS1 expression was normalized to expression of the ACTB and RPL32 housekeeping genes. To analyze hypermethylation, genomic DNA was isolated from 44 tumor CRC biopsies, and methylation-specific PCR was performed. Microsatellite instability (MSI) status was checked with PCR using BAT26, BAT25, and BAT40 markers in the genomic DNA of 84 CRC patients, followed by denaturing gel electrophoresis.

RESULTS

Decreased LATS1 expression was found in 127/142 (89.4%) CRC cases with the average ratio of the LATS1 level 10.33 ± 32.64 in CRC patients vs 32.85 ± 33.56 in healthy controls. The lowest expression was found in Dukes' B stage tumors and G1 (well-differentiated) cells. Hypermethylation of the LATS1 promoter was present in 25/44 (57%) CRC cases analyzed. LATS1 promoter hypermethylation was strongly associated with decreased gene expression; methylated cases showed 162× lower expression of LATS1 than unmethylated cases. Although high-grade MSI (mutation in all three markers) was found in 14/84 (17%) cases and low-grade MSI (mutation in 1-2 markers) was found in 30/84 (36%) cases, we found no association with LATS1 expression.

CONCLUSION

Decreased expression of LATS1 in CRC was associated with promoter hypermethylation, but not MSI status. Such reduced expression may promote progression of CRC.

Differential mucin phenotypes and their significance in a variation of colorectal carcinoma

AIM: To investigate mucin expression profiles in colorectal carcinoma (CRC) histological subtypes with regard to clinicopathologic variables and prognosis.

METHODS: Mucin (MUC)2 and MUC5AC expressions were assessed by immunohistochemistry for a total of 250 CRC cases that underwent surgical resection. CRCs included 63 well-to-moderately differentiated adenocarcinomas (WMDAs), 91 poorly differentiated adenocarcinomas (PDAs), 81 mucinous adenocarcinoma (MUAs), and 15 signet-ring cell carcinomas (SRCCs). MUC2 and MUC5AC were scored as positive when ≥ 25% and ≥ 1% of cancer cells were stained positive, respectively. The human mutL homolog 1 and human mutS homolog 2 expressions were assessed by immunohistochemistry in PDAs to investigate mismatch-repair (MMR) status. Tumors that did not express either of these two were considered MMR-deficient. Results were analyzed for associations with clinicopathologic variables and the prognosis in individual histological CRC subtypes.

RESULTS: MUC2-positive and MUC5AC-positive WMDA percentages were 49.2% and 30.2%, respectively. In contrast, MUC2-positive and MUC5AC-positive PDA percentages were 9.5% and 51.6%, respectively. MUC2 levels tended to decrease and MUC5AC levels tended to increase from WMDA to PDA. In 21 tumors comprising both adenoma and adenocarcinoma components in a single tumor (4 WMDAs, 7 PDAs, and 10 MUAs), MUC2 was significantly downregulated in PDA and MUC5AC was downregulated in PDA and MUA in the adenoma-carcinoma sequence. These results suggested that MUC2 levels might be associated with malignant potential and that MUC5AC expression was an early event in tumorigenesis. Despite worse prognoses than WMDA, high MUC2 expression levels were maintained in MUA (95.1%) and SRCC (71.5%), which suggested a pathogenesis for these subtypes distinct from that of WMDA. No significant associations were found between MUC2 expression and any clinicopathologic variables in any histological subtype. MUC5AC expression in PDA was closely associated with right-sided location (P = 0.017), absence of nodal metastasis (P = 0.010), low tumor node metastasis stage (P = 0.010), and MMR deficiency (P = 0.003). MUC2 expression in WMDA was a marginal prognostic factor for recurrence/metastasis-free survival (RFS) by univariate Cox analysis (P = 0.077) but not by multivariate Cox analysis (P = 0.161). MUC5AC expression in PDA was a significant prognostic factor for RFS by univariate Cox analysis (P = 0.007) but not by multivariate Cox analysis (P = 0.104). Kaplan-Meier curves and log-rank tests revealed that MUC2 expression was marginally associated with a better WMDA prognosis [P = 0.064 for RFS and P = 0.172 for overall survival (OS)] but not for PDA. In contrast, MUC5AC expression was significantly and marginally associated with a better PDA prognosis in terms of RFS and OS, respectively (P = 0.004 for RFS and P = 0.100 for OS), but not for WMDA and MUA.

CONCLUSION: Mucin core protein expression profiles and clinical significance differ according to histological CRC subtypes. This may reflect different pathogeneses for these tumors.