Microsatellite instability in human solid tumors

Clinical prospects of WRN inhibition as a treatment for MSI tumours

The discovery of synthetic lethal interactions with genetic deficiencies in cancers has highlighted several candidate targets for drug development, with variable clinical success. Recent work has unveiled a promising synthetic lethal interaction between inactivation/inhibition of the WRN DNA helicase and tumours with microsatellite instability, a phenotype that arises from DNA mismatch repair deficiency. While these and further studies have highlighted the therapeutic potential of WRN inhibitors, compounds with properties suitable for clinical exploitation remain to be described. Furthermore, the complexities of MSI development and its relationship to cancer evolution pose challenges for clinical prospects. Here, we discuss possible paths of MSI tumour development, the viability of WRN inhibition as a strategy in different scenarios, and the necessary conditions to create a roadmap towards successful implementation of WRN inhibitors in the clinic.

Clinical and Pathological Risk Factors Associated with Liver Fibrosis and Steatosis in African-Americans with Chronic Hepatitis C

BACKGROUND AND AIM

Several factors involved in the development of liver fibrosis in African-American patients with chronic hepatitis C have not been well studied. We aimed to evaluate some of these risk factors.

METHODS

We reviewed pathology and medical records of 603 African-Americans with chronic hepatitis C virus (HCV) infection at Howard University Hospital from January 2004 to December 2013. Among the clinical and pathological data collected were HIV (human immunodeficiency virus), HCV genotype, hepatitis B virus (HBV), diabetes mellitus (DM), hypertension (HTN), body mass index (BMI), and hepatic steatosis.

RESULTS

The frequency of DM, HTN, HIV, and HBV was 22, 16, 11, and 4%, respectively. Median BMI was 27.3 kg/m². The frequency of fibrosis stages 0, 1, 2, 3, and 4 was 2, 48, 28, 11, and 11%, respectively. In multivariate logistic regression, we found a significant association between liver fibrosis stage (3-4 vs. 0-2) and HIV infection (OR 2.4, P = 0.026), HTN (OR 3.0, P = 0.001), age (OR 2.6 for every 10 years, P < 0.001), weight (OR 1.1 for every 10 lb increase, P = 0.002), and steatosis grade (OR 1.6, P = 0.002). The frequency of liver steatosis was 73%. In an ordinal logistic regression, significant risk factors for steatosis were female gender (OR 1.5, P = 0.034) and inflammation grade (P = 0.001).

CONCLUSION

This study shows that steatosis is independently associated with fibrosis in African-American patients with HCV infection. Female patients were at higher risk of steatosis.

Multilevel genomics of colorectal cancers with microsatellite instability-clinical impact of JAK1 mutations and consensus molecular subtype 1

BACKGROUND

Approximately 15% of primary colorectal cancers have DNA mismatch repair deficiency, causing a complex genome with thousands of small mutations-the microsatellite instability (MSI) phenotype. We investigated molecular heterogeneity and tumor immunogenicity in relation to clinical endpoints within this distinct subtype of colorectal cancers.

METHODS

A total of 333 primary MSI+ colorectal tumors from multiple cohorts were analyzed by multilevel genomics and computational modeling-including mutation profiling, clonality modeling, and neoantigen prediction in a subset of the tumors, as well as gene expression profiling for consensus molecular subtypes (CMS) and immune cell infiltration.

RESULTS

Novel, frequent frameshift mutations in four cancer-critical genes were identified by deep exome sequencing, including in CRTC1, BCL9, JAK1, and PTCH1. JAK1 loss-of-function mutations were validated with an overall frequency of 20% in Norwegian and British patients, and mutated tumors had up-regulation of transcriptional signatures associated with resistance to anti-PD-1 treatment. Clonality analyses revealed a high level of intra-tumor heterogeneity; however, this was not associated with disease progression. Among the MSI+ tumors, the total mutation load correlated with the number of predicted neoantigens (P = 4 × 10-5), but not with immune cell infiltration-this was dependent on the CMS class; MSI+ tumors in CMS1 were highly immunogenic compared to MSI+ tumors in CMS2-4. Both JAK1 mutations and CMS1 were favorable prognostic factors (hazard ratios 0.2 [0.05-0.9] and 0.4 [0.2-0.9], respectively, P = 0.03 and 0.02).

CONCLUSIONS

Multilevel genomic analyses of MSI+ colorectal cancer revealed molecular heterogeneity with clinical relevance, including tumor immunogenicity and a favorable patient outcome associated with JAK1 mutations and the transcriptomic subgroup CMS1, emphasizing the potential for prognostic stratification of this clinically important subtype. See related research highlight by Samstein and Chan 10.1186/s13073-017-0438-9.

Luminescent platinum(II) complexes with functionalized N-heterocyclic carbene or diphosphine selectively probe mismatched and abasic DNA

The selective targeting of mismatched DNA overexpressed in cancer cells is an appealing strategy in designing cancer diagnosis and therapy protocols. Few luminescent probes that specifically detect intracellular mismatched DNA have been reported. Here we used Pt(II) complexes with luminescence sensitive to subtle changes in the local environment and report several Pt(II) complexes that selectively bind to and identify DNA mismatches. We evaluated the complexes' DNA-binding characteristics by ultraviolet/visible absorption titration, isothermal titration calorimetry, nuclear magnetic resonance and quantum mechanics/molecular mechanics calculations. These Pt(II) complexes show up to 15-fold higher emission intensities upon binding to mismatched DNA over matched DNA and can be utilized for both detecting DNA abasic sites and identifying cancer cells and human tissue samples with different levels of mismatch repair. Our work highlights the potential of luminescent Pt(II) complexes to differentiate between normal cells and cancer cells which generally possess more aberrant DNA structures.

DNA pairing defects such as mismatched and abasic DNA are prevalent in cancer cells. Here, the authors present luminescent platinum based probes capable of preferentially binding to mismatched and abasic DNA, and reporting this by a significant luminescence enhancement

Transcriptome instability as a molecular pan-cancer characteristic of carcinomas

BACKGROUND

We have previously proposed transcriptome instability as a genome-wide, pre-mRNA splicing-related characteristic of colorectal cancer. Here, we explore the hypothesis of transcriptome instability being a general characteristic of cancer.

RESULTS

Exon-level microarray expression data from ten cancer datasets were analyzed, including breast cancer, cervical cancer, colorectal cancer, gastric cancer, lung cancer, neuroblastoma, and prostate cancer (555 samples), as well as paired normal tissue samples from the colon, lung, prostate, and stomach (93 samples). Based on alternative splicing scores across the genomes, we calculated sample-wise relative amounts of aberrant exon skipping and inclusion. Strong and non-random (P < 0.001) correlations between these estimates and the expression levels of splicing factor genes (n = 280) were found in most cancer types analyzed (breast-, cervical-, colorectal-, lung- and prostate cancer). This suggests a biological explanation for the splicing variation. Surprisingly, these associations prevailed in pan-cancer analyses. This is in contrast to the tissue and cancer specific patterns observed in comparisons across healthy tissue samples from the colon, lung, prostate, and stomach, and between paired cancer-normal samples from the same four tissue types.

CONCLUSION

Based on exon-level expression profiling and computational analyses of alternative splicing, we propose transcriptome instability as a molecular pan-cancer characteristic. The affected cancers show strong and non-random associations between low expression levels of splicing factor genes, and high amounts of aberrant exon skipping and inclusion, and vice versa, on a genome-wide scale.

DNA content analysis of colorectal cancer defines a distinct 'microsatellite and chromosome stable' group but does not predict response to radiotherapy

Colorectal cancers (CRC) are thought to have genetic instability in the form of either microsatellite instability (MSI) or chromosomal instability (CIN). Recently, tumours have been described without either MSI or CIN, that is, microsatellite and chromosome stable (MACS) CRCs. We investigated the (i) frequency of the MACS-CRCs and (ii) whether this genotype predicted responsiveness to neoadjuvant chemoradiotherapy. To examine the frequency of MACS-CRCs, DNA content (ploidy) was examined in 89 sporadic microsatellite-stable CRCs using flow cytometry. The tumours were also screened for mutations in KRAS/BRAF/TP53/PIK3CA by QMC-PCR. To examine the value of tumour ploidy in predicting response to chemoradiotherapy, DNA content was tested in a separate group of 62 rectal cancers treated with neoadjuvant chemoradiotherapy. Fifty-one of 89 CRCs (57%) were aneuploid and 38 (43%) were diploid. There was no significant association between mutations in TP53/KRAS/BRAF/PIK3CA and ploidy. Testing of association between mutations revealed only mutual exclusivity of KRAS/BRAF mutation (P < 0.001). Of the 62 rectal cancers treated with neoadjuvant chemoradiotherapy, 22 had responded (Mandard tumour regression grade 1/2) and 40 failed to respond (Grade 3-5). Twenty-five of 62 (40%) tumours were diploid, but there was no association between ploidy and response to therapy. We conclude that MACS-CRCs form a significant proportion of microsatellite-stable CRCs with a mutation profile overlapping that of CRCs with CIN. A diploid genotype does not, however, predict the responsiveness to radiotherapy.

Epigenetic and genetic features of 24 colon cancer cell lines

Cell lines are invaluable biomedical research tools, and recent literature has emphasized the importance of genotype authentication and characterization. In the present study, 24 out of 27 cell line identities were confirmed by short tandem repeat profiling. The molecular phenotypes of the 24 colon cancer cell lines were examined, and microsatellite instability (MSI) and CpG island methylator phenotype (CIMP) were determined, using the Bethesda panel mononucleotide repeat loci and two epimarker panels, respectively. Furthermore, the BRAF, KRAS and PIK3CA oncogenes were analyzed for mutations in known hotspots, while the entire coding sequences of the PTEN and TP53 tumor suppressors were investigated. Nine cell lines showed MSI. Thirteen and nine cell lines were found to be CIMP positive, using the Issa panel and the Weisenberger et al. panel, respectively. The latter was found to be superior for CIMP classification of colon cancer cell lines. Seventeen cell lines harbored disrupting TP53 mutations. Altogether, 20/24 cell lines had the mitogen-activated protein kinase pathway activating mutually exclusive KRAS or BRAF mutations. PIK3CA and PTEN mutations leading to hyperactivation of the phosphoinositide 3-kinase/AKT pathway were observed in 13/24 cell lines. Interestingly, in four cell lines there were no mutations in neither BRAF, KRAS, PIK3CA nor in PTEN. In conclusion, this study presents molecular features of a large number of colon cancer cell lines to aid the selection of suitable in vitro models for descriptive and functional research.

DNA sequence profiles of the colorectal cancer critical gene set KRAS-BRAF-PIK3CA-PTEN-TP53 related to age at disease onset

The incidence of colorectal cancer (CRC) increases with age and early onset indicates an increased likelihood for genetic predisposition for this disease. The somatic genetics of tumor development in relation to patient age remains mostly unknown. We have examined the mutation status of five known cancer critical genes in relation to age at diagnosis, and compared the genomic complexity of tumors from young patients without known CRC syndromes with those from elderly patients. Among 181 CRC patients, stratified by microsatellite instability status, DNA sequence changes were identified in KRAS (32%), BRAF (16%), PIK3CA (4%), PTEN (14%) and TP53 (51%). In patients younger than 50 years (n = 45), PIK3CA mutations were not observed and TP53 mutations were more frequent than in the older age groups. The total gene mutation index was lowest in tumors from the youngest patients. In contrast, the genome complexity, assessed as copy number aberrations, was highest in tumors from the youngest patients. A comparable number of tumors from young (<50 years) and old patients (>70 years) was quadruple negative for the four predictive gene markers (KRAS-BRAF-PIK3CA-PTEN); however, 16% of young versus only 1% of the old patients had tumor mutations in PTEN/PIK3CA exclusively. This implies that mutation testing for prediction of EGFR treatment response may be restricted to KRAS and BRAF in elderly (>70 years) patients. Distinct genetic differences found in tumors from young and elderly patients, whom are comparable for known clinical and pathological variables, indicate that young patients have a different genetic risk profile for CRC development than older patients.

Distinct high resolution genome profiles of early onset and late onset colorectal cancer integrated with gene expression data identify candidate susceptibility loci

Background

Estimates suggest that up to 30% of colorectal cancers (CRC) may develop due to an increased genetic risk. The mean age at diagnosis for CRC is about 70 years. Time of disease onset 20 years younger than the mean age is assumed to be indicative of genetic susceptibility. We have compared high resolution tumor genome copy number variation (CNV) (Roche NimbleGen, 385 000 oligo CGH array) in microsatellite stable (MSS) tumors from two age groups, including 23 young at onset patients without known hereditary syndromes and with a median age of 44 years (range: 28-53) and 17 elderly patients with median age 79 years (range: 69-87). Our aim was to identify differences in the tumor genomes between these groups and pinpoint potential susceptibility loci. Integration analysis of CNV and genome wide mRNA expression data, available for the same tumors, was performed to identify a restricted candidate gene list.

Results

The total fraction of the genome with aberrant copy number, the overall genomic profile and the TP53 mutation spectrum were similar between the two age groups. However, both the number of chromosomal aberrations and the number of breakpoints differed significantly between the groups. Gains of 2q35, 10q21.3-22.1, 10q22.3 and 19q13.2-13.31 and losses from 1p31.3, 1q21.1, 2q21.2, 4p16.1-q28.3, 10p11.1 and 19p12, positions that in total contain more than 500 genes, were found significantly more often in the early onset group as compared to the late onset group. Integration analysis revealed a covariation of DNA copy number at these sites and mRNA expression for 107 of the genes. Seven of these genes, CLC, EIF4E, LTBP4, PLA2G12A, PPAT, RG9MTD2, and ZNF574, had significantly different mRNA expression comparing median expression levels across the transcriptome between the two groups.

Conclusions

Ten genomic loci, containing more than 500 protein coding genes, are identified as more often altered in tumors from early onset versus late onset CRC. Integration of genome and transcriptome data identifies seven novel candidate genes with the potential to identify an increased risk for CRC.

Map and analysis of microsatellites in the genome of Populus: the first sequenced perennial plant

We mapped and analyzed the microsatellites throughout 284295605 base pairs of the unambiguously assembled sequence scaffolds along 19 chromosomes of the haploid poplar genome. Totally, we found 150985 SSRs with repeat unit lengths between 2 and 5 bp. The established microsatellite physical map demonstrated that SSRs were distributed relatively evenly across the genome of Populus. On average, These SSRs occurred every 1883 bp within the poplar genome and the SSR densities in intergenic regions, introns, exons and UTRs were 85.4%, 10.7%, 2.7% and 1.2%, respectively. We took di-, tri-, tetra-and pentamers as the four classes of repeat units and found that the density of each class of SSRs decreased with the repeat unit lengths except for the tetranucleotide repeats. It was noteworthy that the length diversification of microsatellite sequences was negatively correlated with their repeat unit length and the SSRs with shorter repeat units gained repeats faster than the SSRs with longer repeat units. We also found that the GC content of poplar sequence significantly correlated with densities of SSRs with uneven repeat unit lengths (tri-and penta-), but had no significant correlation with densities of SSRs with even repeat unit lengths (di-and tetra-). In poplar genome, there were evidences that the occurrence of different microsatellites was under selection and the GC content in SSR sequences was found to significantly relate to the functional importance of microsatellites.

Elevated microsatellite alterations at selected tetranucleotides (EMAST) and mismatch repair gene expression in prostate cancer

Elevated microsatellite alterations at selected tetranucleotides (EMAST), a new form of microsatellite instability (MSI) affecting tetranucleotide repeats, was recently described to be frequent in several tumor types (e.g., bladder, lung, ovarian, and skin cancers). EMAST was found as a form of microsatellite alteration distinct from the MSI phenotype in hereditary nonpolyposis colorectal cancer (HNPCC)-related tumors which mostly affects mono- and dinucleotide repeats. To date, no study has investigated the role of EMAST in prostate cancer. We therefore analyzed 81 prostate tumors using 10 markers frequently detecting EMAST in other cancer types and the National Cancer Institute-consensus panel for HNPCC detection plus BAT40. In addition, we investigated p53 gene alterations [loss of heterozygosity (LOH)] and the expression of p53 and the mismatch repair (MMR) genes hMLH1 and hMSH2 on tissue microarrays. EMAST was detected in 4/81 (5%) cases and MSI in 6/79 (7.6%) cases. LOH of p53 was found in 9/45 (20%) informative cases. There was no correlation between MSI status and the histopathological or molecular characteristics of the tumors. Immunohistochemistry revealed p53 positivity in 5/61 (8%) tumors. There was a significant correlation between tumors showing a recurrence within 3 years after treatment and p53 positivity (p=0.029). Reduced hMLH1 expression, but no complete loss, was detected in 9/41 (22%) tumors without any correlations to histopathological or clinical features. Analysis of hMSH2 expression was available from 58/81 (72%) tumors. Staining intensity was as follows: negative in 7/58 (12%), weak staining in 16/58 (27.5%) samples, moderate staining in 19/58 (33%) samples, and strong staining in 16/58 (27.5%) samples. When negative/weak staining and moderate/strong staining were considered as two groups, there was a significant association between hMSH2 expression and tumor recurrence (p=0.039). In conclusion, our data show that MSI and EMAST are infrequent but distinct patterns of MSI in prostate tumors not related to MMR defects, p53 alterations, and histopathological characteristics. p53 positivity and moderate to strong hMSH2 expression of prostate tumors are correlated with early disease recurrence and indicate an unfavorable clinical course of the disease. These two genes could be useful biomarkers for the prediction of patients' outcome and should be analyzed in prospective studies.

Molecular mechanisms of human carcinogenesis

Intensive research efforts during the last several decades have increased our understanding of carcinogenesis, and have identified a genetic basis for the multi-step process of cancer development. Tumors grow through a process of clonal expansion driven by mutation. Several forms of molecular alteration have been described in human cancers, and these can be generally classified as chromosomal abnormalities and nucleotide sequence abnormalities. Most cancer cells display a phenotype characterized by genomic hypermutability, suggesting that genomic instability may precede the acquisition of transforming mutations in critical target genes. Reduced to its essence, cancer is a disease of abnormal gene expression, and these genetic abnormalities contribute to cancer pathogenesis through inactivation of negative mediators of cell proliferation (including tumor suppressor genes) and activation of positive mediators of cell proliferation (including proto-oncogenes). In several human tumor systems, specific genetic alterations have been shown to correlate with well-defined histopathological stages of tumor development and progression. Although the significance of mutations to the etiological mechanisms of tumor development has been debated, a causal role for such genetic lesions is now commonly accepted for most human cancers. Thus, genetic lesions represent an integral part of the processes of neoplastic transformation, tumorigenesis, and tumor progression, and as such represent potentially valuable markers for cancer detection and staging.

Microsatellite instability of selective target genes in HNPCC-associated colon adenomas

Microsatellite instability (MSI) occurs in most hereditary nonpolyposis colorectal cancers (HNPCC) and less frequently in sporadic tumors as the result of DNA mismatch repair (MMR) deficiency. Instability at coding microsatellites (cMS) in specific target genes causes frameshift mutations and functional inactivation of affected proteins, thereby providing a selective growth advantage to MMR deficient cells. At present, little is known about Selective Target Gene frameshift mutations in preneoplastic lesions. In this study, we examined 30 HNPCC-associated MSI-H colorectal adenomas of different grades of dysplasia for frameshift mutations in 26 cMS-bearing genes, which, according to our previous model, represent Selective Target genes of MSI. About 30% (8/26) of these genes showed a high mutation frequency (> or =50%) in colorectal adenomas, similar to the frequencies reported for colorectal carcinomas. Mutations in one gene (PTHL3) occurred significantly less frequently in MSI adenomas compared to published mutation rates in MSI carcinomas (36.0 vs 85.7%, P=0.023). Biallelic inactivation was observed in nine genes, thus emphasizing the functional impact of cMS instability on MSI tumorigenesis. Some genes showed a high frequency of frameshift mutations already at early stages of MSI colorectal tumorigenesis that increased with grade of dysplasia and transition to carcinoma. These include known Target Genes like BAX and TGFBR2, as well as three novel candidates, MACS, NDUFC2, and TAF1B. Overall, we have identified genes of potential relevance for the initiation and progression of MSI tumorigenesis, thus representing promising candidates for novel diagnostic and therapeutic approaches directed towards MMR-deficient tumors.

Genetic instability in primary leiomyosarcoma of bone

Primary leiomyosarcoma (LMS) of bone is an exceedingly rare entity on which to date no molecular data have been reported. In a series of 6 tumors (5 grade IIB, 1 grade IIA), we assessed the prevailing genetic stability by microsatellite analysis at 7 loci. The IIB tumors demonstrated a rate of genomic loss as high as 90%, accompanied by an intratumoral heterogeneity in 30% of conspicuous markers. High microsatellite instability in the severe type was not observed, although hMLH1 immunostaining was consistently negative. We assume that intraosseous LMS pertains to "deletor phenotype" tumors. We did observe a locus-specific MSI in our marker linked with hMSH2. Immunostaining and allelotyping indicated a knock-out of pRb in all cases, confirming its major role in sarcomas. Only the stage IIB tumors (4 of 5) pointed to p53 inactivation. In addition, the human telomerase subunit-linked markers exhibited high rates of chromosomal loss. The stage IIA tumor still confined to the bone displayed no genetic instability. Moreover, the proliferation index made a clear distinction between the IIA and IIB tumors (5% vs 30%). We propose to further investigate the usefulness of loss of heterozygosity as a progression marker in this entity.

The evolutionary origin of genetic instability in cancer development

The standard model of carcinogenesis is currently being questioned. The main controversy concerns genetic instability and has links to fundamental questions in evolutionary biology. This paper aims to clarify the underlying conflict between the linear configuration of the standard model and the non-linear dynamics of Darwinian evolution. It addresses the problem of applying the concept of clonal selection to genetically unstable cells and presents an alternative perspective based on the principles of molecular evolution. This model explains genetic instability in terms of competition between genetic strategies and draws lines to basic aspects of evolutionary biology.

Genome signatures of colon carcinoma cell lines

In cancer biology, cell lines are often used instead of primary tumors because of their widespread availability and close reflection of the in vivo state. Cancer is a genetic disease, commonly caused by small- and large-scale DNA rearrangements. Therefore, it is essential to know the genomic profiles of tumor cell lines to enable their correct and efficient use as experimental tools. Here, we present a comprehensive study of the genomic profiles of 20 colon cancer cell lines combining conventional karyotyping (G-banding), comparative genomic hybridization (CGH), and multicolor fluorescence in situ hybridization (M-FISH). Major differences between the microsatellite instability (MSI) and chromosome instability (CIN) cell lines are shown; the CIN cell lines exhibited complex karyotypes involving many chromosomes (mean: 8.5 copy number changes), whereas the MSI cell lines showed considerably fewer aberrations (mean: 2.6). The 3 techniques complement each other to provide a detailed picture of the numerical and structural chromosomal changes that characterize cancer cells. Therefore, 7 of the cell lines (Colo320, EB, Fri, IS2, IS3, SW480, and V9P) are here completely karyotyped for the first time and, among these, 5 have not previously been cytogenetically described. By hierarchical cluster analysis, we show that the cell lines are representative models for primary carcinomas at the genome level. We also present the genomic profiles of an experimental model for tumor progression, including 3 cell lines (IS1, IS2, and IS3) established from a primary carcinoma, its corresponding liver- and peritoneal metastasis from the same patient. To address the question of clonality, we compared the genome of 3 common cell lines grown in 2 laboratories. Finally, we compared all our results with previously published CGH data and karyotypes of colorectal cell lines. In conclusion, the large variation in genetic complexity of the cell lines highlights the importance of a comprehensive reference of genomic profiles for investigators engaged in functional studies using these research tools.

Instability of microsatellites is an infrequent event in uveal melanoma

Microsatellite instability (MSI) is a distinct tumour phenotype that is associated with alterations of DNA mismatch repair and is being increasingly reported in a number of hereditary and sporadic tumours. Numerous reports have suggested that melanocytic neoplasms, including cutaneous melanomas, frequently demonstrate low frequency MSI, whilst a small number of tumours exhibit high frequency MSI. Furthermore, loss of expression of DNA mismatch repair proteins has been associated with progression from benign to malignant disease in melanocytic neoplasms, but the presence or absence of mismatch repair defects in uveal melanomas has yet to be determined. This study was designed to establish whether MSI is a feature of these ocular melanomas. To investigate the prevalence of MSI in uveal melanomas, 52 tumours were analysed by polymerase chain reaction amplification of a panel of microsatellite markers selected for their ability to detect tumours exhibiting defects in DNA mismatch repair mechanisms. MSI was rarely detected in the 52 uveal melanomas analysed. All tumours demonstrated stable microsatellites at five of the six microsatellite markers tested (BAT26, BAT40, APC, D2S123 and Mfd15CA). Only one tumour showed the presence of a single unstable allele at a tetranucleotide marker (MYCL1). These data suggest that high frequency MSI does not occur in these tumours, and that low frequency MSI, in contrast to cutaneous melanoma, is a rare event in malignant melanomas of the uveal tract.

Mitochondrial DNA and human thyroid diseases

Cells of the thyroid tissue, either diseased or normal, can accumulate altered mitochondrial genomes in primary lesions and in surrounding parenchyma. Depending on the experimental approaches and the extent of the mutational process, it has been possible to demonstrate the occurrence of homoplasmic or heteroplasmic point mutations, presence of a common deletion and random large-scale mtDNA aberrations in various pathological states. Point somatic mutations documented in 5-60% of thyroid tumors do not concentrate in obvious hotspots but tend to cluster in certain regions of the mitochondrial genome and their distribution may differ between carcinomas and controls. Large-scale deletions in mtDNA are quite prevalent in healthy and diseased thyroid; however, the proportion of aberrant mtDNA molecules accounts for a very small part of total mtDNA and does not seem to correlate with pathological characteristics of thyroid tumors. Common deletion is most abundant in Hurthle cell tumors, yet it also occurs in other thyroid diseases as well as in normal tissue. The principal difference between the common deletion and other deletion-type mtDNA molecules is that the former does not depend on the relative mtDNA content in the tissue whereas in a subset of thyroid tumors, such as radiation-associated papillary carcinomas and follicular adenomas, there is a strong correlation between mtDNA levels and prevalence of large-scale deletions. Relative mtDNA levels by themselves are elevated in most thyroid tumors compared to normal tissue. Distinct differential distribution and prevalence of mutational mtDNA burden in normal tissue and thyroid lesions are suggestive of the implication of altered mtDNA in thyroid diseases, especially in cancer.

DNA variants in the ATM gene are not associated with sporadic rectal cancer in a Norwegian population-based study

BACKGROUND AND AIMS

A large number of DNA single-nucleotide polymorphisms (SNPs) have been discovered following the Human Genome Project. Several projects have been launched to find associations between SNPs and various disease cohorts. This study examined the possible association between the reported SNPs and sporadic rectal cancer. It has been proposed that SNPs in the ataxi-telangiectasia mutated (ATM) gene modulate the penetrance of some cancers. The investigated target sequence harbors three polymorphisms (IVS38-8 T/C in intron 38, 5557 G/A and 5558 A/T in exon 39), resulting in eight possible microhaplotypes at the DNA level. Furthermore, the two exonic SNPs are sited next to each other, allowing four possible amino acids in the same codon.

METHODS

We report on a new method analyzing SNPs and microhaplotypes based on theoretical thermodynamics and migration of variant fragments by cycling temperature capillary electrophoresis. Fluorophore-labeled PCR products were analyzed without any post-PCR steps on a standard 96 capillary-sequencing instrument under denaturing conditions.

RESULTS

More than 7000 alleles were microhaplotyped based on peak migration patterns of individual samples and sequencing results. The ATM polymorphisms and microhaplotypes examined did not significantly differ between sporadic rectal cancer and normal population.

CONCLUSION

No associations were found between the IVS38-8 T/C, 5557 G/A and 5558 A/T polymorphisms and microhaplotypes in the ATM gene with respect to sporadic rectal cancer.

The role of mismatch repair in small-cell lung cancer cells

The role of mismatch repair (MMR) in small-cell lung cancer (SCLC) is controversial, as the phenotype of a MMR-deficiency, microsatellite instability (MSI), has been reported to range from 0 to 76%. We studied the MMR pathway in a panel of 21 SCLC cell lines and observed a highly heterogeneous pattern of MMR gene expression. A significant correlation between the mRNA and protein levels was found. We demonstrate that low hMLH1 gene expression was not linked to promoter CpG methylation. One cell line (86MI) was found to be deficient in MMR and exhibited resistance to the alkylating agent MNNG. Surprisingly, MSI was not detected in 86MI and it appears to express all the major MMR components hMSH2, hMSH6, hMLH1, hPMS2, hMSH3, hMLH3, MBD4 (MED1) and hExo1. These data are consistent with at least two possibilities: (1) A missense mutation in one of the MMR genes, which dissociates MSI from drug resistance, or (2) inactivation of a second pathway that leads to MMR-deficiency and MNNG resistance, but induces negligible levels of MSI. We conclude that MMR deficiency is largely not associated with the pathogenesis of SCLC.

Alu profiling of primary and metastatic nonsmall cell lung cancer

The metastatic potential of nonsmall cell carcinoma of lung (NSCLC), is currently recognized post factum, when lymph nodes or distant organs are already involved. Our ability to determine which tumors have acquired metastatic potential could help direct therapy to be more aggressive or less aggressive based upon this information. Evaluation of microsatellite instability via detection of LOH at specific loci may be useful in identifying specific markers and/or genes associated with this process. We examined Alu insertional elements as a potential marker of genetic changes associated with the metastatic potential of NSCLC. We analyzed archived, paraffin embedded tissue from 20 proven cases of NSCLC. DNA was extracted from 10 micron paraffin sections and amplified using an Alu PCR protocol. This technique does not examine specific loci but rather results in a banding profile of cellular genomic DNA. Informative allelic banding patterns, noted as differences between primary and metastatic lesions from the same patient, were observed in five of six cases (83%) with intrapulmonary metastases and in only nine of 14 (64%) cases with extrapulmonary metastases. Multiple genomic changes were detected in metastatic tumor cells as compared to normal lung tissue or primary lung tumor tissue. It appears that Alu profiling may be useful in the detection of metastatic vs primary lesions, and this technique may offer a method for identifying novel genes responsible for tumor progression and metastases.

Adenovirus-mediated gene transfer of P16INK4/CDKN2 into bax-negative colon cancer cells induces apoptosis and tumor regression in vivo

The tumor-suppressor gene p16INK4/CDKN2 (p16) is a cyclin-dependent kinase (cdk) inhibitor and important cell cycle regulator. Here, we show that adenovirus-mediated gene transfer of p16 (AdCMV.p16) into colon cancer cells induces uncoupling of S phase and mitosis and subsequently apoptosis. Flow cytometric analysis revealed that cells infected with AdCMV.p16 showed an initial G2-like arrest followed by S phase without intervening mitosis (DNA >4N). Using microscopic analysis, deformed polyploid cells were detectable only in cells infected with AdCMV.p16 but not in control-infected cells. Subsequently, AdCMV.p16-infected polyploid cells underwent apoptosis, as assessed by AnnexinV staining and DNA fragmentation, suggesting that cell cycle dysregulation is upstream of the onset of apoptosis. Treatment of mice with subcutaneously transplanted tumors of colorectal cancer cells with AdCMV.p16 but not AdCMV.p53 resulted in significantly reduced tumor volume and prolonged survival. Using an orthotopic model of liver metastasis, we observed both reduced local tumor growth and secondary intrahepatic metastasis after AdCMV.p16 treatment. Importantly, induction of apoptosis in vitro and reduction of tumor growth in vivo by p16 was p53- as well as bax-independent because identical results were obtained using cancer cells, either wild type or mutant for p53 or bax. The studies suggest that an AdCMV.p16-based treatment may be especially effective in patients with bax-negative colon cancer where overexpression of p53 appears not to be of therapeutic value.

Microsatellite instability and cytogenetic survey in myeloid leukemias

Microsatellites are short tandem repeat sequences dispersed throughout the genome. Their instability at multiple genetic loci may result from mismatch repair errors and it occurs in hereditary nonpolyposis colorectal cancer. This instability is also found in many sporadic cancers. In order to evaluate the importance of this process in myeloid leukemias, we studied five loci in different chromosomes of 43 patients, 22 with chronic myelocytic leukemia (CML) in the chronic phase, 7 with CML in blast crisis, and 14 with acute myeloid leukemia (AML), by comparing leukemic DNA extracted from bone marrow and constitutional DNA obtained from buccal epithelial cells. Only one of the 43 patients (2.1%), with relapsed AML, showed an alteration in the allele length at a single locus. Cytogenetic analysis was performed in order to improve the characterization of leukemic subtypes and to determine if specific chromosome aberrations were associated with the presence of microsatellite instability. Several chromosome aberrations were observed, most of them detected at diagnosis and during follow-up of the patients, according to current literature. These findings suggest that microsatellite instability is an infrequent genetic event in myeloid leukemias, adding support to the current view that the mechanisms of genomic instability in solid tumors differ from those observed in leukemias, where specific chromosome aberrations seem to play a major role.

WNT1 inducible signaling pathway protein 3, WISP-3, a novel target gene in colorectal carcinomas with microsatellite instability

BACKGROUND & AIMS

Microsatellite instability (MSI) is the phenotype of colorectal carcinomas with defect mismatch repair. Genes with repetitive sequences within their coding regions are targets for mutations in these tumors. We have evaluated 2 novel candidate genes for potential involvement in development of MSI colorectal carcinomas and compared them with alterations in known target genes.

METHODS

The MSI status was determined by multiplex polymerase chain reactions (PCRs) of 5-17 markers in a Norwegian series of 275 colorectal carcinomas. All MSI tumors were analyzed for gene mutations using fluorescence PCR followed by capillary electrophoresis. Two novel candidate genes, WNT1-inducible signaling pathway protein 3 (WISP-3) and caspase-1, and 9 known target genes were analyzed.

RESULTS

Thirteen percent of the tumors were MSI-high (H) and 12% were MSI-low (L). Thirty-three of 37 MSI-H vs. 1 of 34 MSI-L tumors showed mutations in the target genes (P < 0.001). WISP-3 was mutated in 31% of the MSI-H tumors. The frequencies of frameshift mutations in the known target genes were comparable with other studies.

CONCLUSIONS

The relative high frequency of mutation, higher than those seen for other known target genes, the predicted truncation of the protein product, and the homology with WISP-1 and WISP-2, 2 proteins induced downstream of WNT1 signaling, strongly suggest WISP-3 as a novel target in development of MSI-H colorectal carcinomas.

Functional analysis of the mismatch repair system in bladder cancer

In bladder cancer the observed microsatellite instability indicates that mismatch repair deficiency could be a frequently involved factor in bladder cancer progression. To investigate this hypothesis we analysed extracts of seven bladder cancer cell lines and, as a novel approach, five clinical cancer samples for mismatch repair activity. We found that one cell line (T24) and three of the clinical samples had a reduced repair capacity, measured to approximately 20% or less. The T24 cell extract was unable to repair a G-G mismatch and showed reduced repair of a 2-base loop, consistent with diminished function of the MSH2-MSH6 heterodimer. The functional assay was combined with measurement for mutation frequency, microsatellite analysis, sequencing, MTT assay, immunohistochemical analysis and RT-PCR analysis of the mismatch repair genes MSH2, MSH3, MSH6, PMS1, PMS2 and MLH1. A >7-fold relative increase in mutation frequency was observed for T24 compared to a bladder cancer cell line with a fully functional mismatch repair system. Neither microsatellite instability, loss of repair nor mismatch repair gene mutations were detected. However, RT-PCR analysis of mRNA levels did detect changes in the ratio of expression of the Mut S and Mut L homologues. The T24 cell line had the lowest MSH6 expression level of the cell lines tested. Identical RT-PCR analysis of seventeen clinical samples (normal urothelium, 7; pTa low stage, 5; and pT1-4 high stage, 5) indicated a significant change in the expression ratio between MSH3/MSH6 (P< 0.004), MSH2/MSH3 (P< 0.012) and PMS2/MLH1 P< 0.005, in high stage bladder tumours compared to normal urothelium and low stage tumours. Collectively, the data suggest that imbalanced expression of mismatch repair genes could lead to partial loss of mismatch repair activity that is associated with invasive bladder cancer.

Caspase-3 activity as a prognostic factor in colorectal carcinoma

Several techniques to determine apoptotic frequencies in tumors have been described. In this study, we report that biochemical detection of enzymatic caspase-3 activity is a simple and quantitative technique to measure apoptosis in colorectal tumor cells. The relevance of the level of apoptosis in colorectal cancer for the clinical course remains unclear. Therefore, we studied the correlation between caspase-3 activity and prognosis of the disease in relation to different factors known to be involved in apoptosis induction. High caspase-3 activity significantly correlated with a higher risk of recurrence and was preferentially found in tumors of the right side of the colon. No correlation was detected between high caspase-3 activity and altered protein expression of p53, beta-catenin, or proteins of mismatched repair genes. This indicates that high caspase-3 activity has no evident correlation with the genetic Wnt-signaling or the mismatch repair mutational pathways. The caspase-3 activity significantly correlated with CD57(+) tumor infiltrating cells. Therefore, high caspase-3 activity in right-sided tumors might be induced by a specific lymphocytic reaction.

p53 Mutations and microsatellite instability in ovarian cancer: Yin and yang

OBJECTIVE

We tested the hypothesis that p53 frameshift mutations in ovarian cancer occur as a result of genomic instability rather than as a proximal cause of this process.

STUDY DESIGN

Sequencing of the p53 tumor suppressor gene has been carried out on 305 ovarian, fallopian tube, and peritoneal cancers. Two groups of p53 null mutations were identified: (1) those caused by frameshift insertion or deletion mutations (n = 31) and (2) those caused by nonsense mutations (n = 28). As a control group 59 tumors with p53 missense mutations were selected by matching with the p53 null tumors on the basis of patient age at diagnosis, stage and grade of cancer, cancer site, and year of diagnosis. Microsatellite instability was determined from paired normal and tumor tissue deoxyribonucleic acid by means of the following different markers: D2S123, D5S346, D17S250, BAT25, and BAT26. Amplimers from polymerase chain reactions were evaluated on 7% polyacrylamide gels.

RESULTS

The p53 null tumors were more likely to be of higher stage and grade. Fallopian tube cancers were more common (P =.02) in the p53 frameshift group. The overall incidence of microsatellite instability was 39%, 36%, and 25% for tumors with p53 frameshift nonsense and missense mutations (P =.30). Microsatellite instability was seen almost exclusively with ovarian cancer (P =.04).

CONCLUSIONS

Microsatellite instability is a relatively common event in ovarian cancer and is dependent on marker selection. The p53 frameshift mutations do not appear to occur as a consequence of genomic instability.

Microsatellite instability as a tool for the classification of gastric cancer

Microsatellite instability (MSI) is a common feature of gastric cancers that reflects underlying mismatch-repair deficiency in the tumor, caused most frequently by methylation of the hMLH1 promoter. Tumors with MSI have been found to inactivate certain target genes by permitting an increased frequency of mutations in mononucleotide runs in their coding regions. Gastric tumors with MSI have a distinct clinicopathological profile with a relatively good prognosis. Using the simple and robust methodologies available, MSI detection in gastrointestinal tumors promises to be one of the first widely used molecular prognostic tests for human cancer. Here, we review the molecular context of this exciting prospect with respect to one of the world's most prevalent cancers, that of the stomach.

Distal deletion of 1p in colorectal tumors: an initial event and/or a step in carcinogenesis? Study by fluorescence in situ hybridization interphase cytogenetics

Cytogenetics studies have suggested that short arm deletion in chromosome 1 is involved in triggering colorectal tumor development. To elucidate the role of 1p under-representation in the tumoral process, we investigated by fluorescence in situ hybridization interphase cytogenetics, using simultaneously centromeric and p36 telomeric probes for chromosome 1, 27 primary adenocarcinomas, 5 metastases, 5 adenomas and as control 4 normal mucous membranes. The 1p under-representation in paradiploid tumoral cells, interpreted as a 1p deletion, was observed in 8/27 adenocarcinomas, 2/5 metastases and 3/5 adenomas. Thus, in diploid cells 1p deletion was observed in some tumors independently of the stage of the process. The 1p under-representation in total number of examined cells, i.e., diploid and aneuploid, was observed in 14/16 grade B1-B2 tumors, in 5/8 grade C1-C2 tumors, and all grade D tumors (3/3) and all metastases (5/5). There were no correlations with location or histological characteristics of cancers, gender or age of patients. These results show high frequency of 1p under-representation in intestinal tumors, and lead to separate the under-representation of 1p in diploid cells, which correspond to a 1p deletion probably implicated in the initiation of the process, from the under-representation in aneuploid cells, which mainly may be the consequence of complex rearrangements in relation to extension of the malignant process.

Evaluation of 1p losses in primary carcinomas, local recurrences and peripheral metastases from colorectal cancer patients

Cytogenetic and molecular genetic analyses of colorectal adenomas and carcinomas have shown that loss of the distal part of chromosome arm 1p is common, particularly in tumors of the left colon. Because the importance of 1p loss in colorectal cancer metastases is unknown, we compared the frequency, exact site and extent of 1p deletions in primary carcinomas (n=28), local recurrences (n=19) and metastases (n=33) from 67 colorectal cancer patients using 14 markers in an allelic imbalance study. Loss of 1p was found in 50% of the primary carcinomas, 33% of the local recurrences, and 64% of the metastases, revealing a significant difference between the local recurrences and the metastases (P=.04). The smallest region of 1p deletion overlap (SRO) defined separately for each group of lesions had the region between markers D1S2647 and D1S2644, at 1p35-36, in common. The genes PLA2G2A (1p35.1-36) and TP73 (1p36.3) were shown to lie outside this consistently lost region, suggesting that neither of them are targets for the 1p loss. In the second part of the study, microdissected primary carcinomas and distant metastases from the same colorectal cancer patients (n=18) were analyzed, and the same 1p genotype was found in the majority of patients (12/18, 67%). The finding that primary carcinoma cells with metastatic ability usually contain 1p deletions, and that some cases lacking 1p alterations in the primary tumor acquire such changes during growth of a metastatic lesion, supports the notion that 1p loss may be important both early and late in colorectal carcinogenesis, with the apparent exception of local recurrences.

Microsatellite instability in ovarian and other pelvic carcinomas

Twenty-six cases of ovarian carcinoma and six cases of other pelvic neoplasms were analyzed for microsatellite instability (MSI) using frozen specimens, fluorescence technology, and four selected markers (D2S123 on chromosome 2, D18S58 on chromosome 18, BAT26 on chromosome 2, and BAT40 on chromosome 1). This procedure also allowed the detection of loss of heterogeneity (LOH) at the four selected loci. One of the cases of ovarian carcinoma exhibited MSI and this was evident at three loci. Of 44 informative loci, 7 exhibited LOH representing 3 cases of ovarian carcinoma, 3 of 4 cases of primary peritoneal carcinoma, and one case of unknown primary. These data support other findings that MSI is not a frequent occurrence in ovarian cancer; however, LOH is a more frequent event and may be a target for the development of diagnostic/prognostic procedures for ovarian and primary peritoneal carcinoma.

Genomic instability, DNA methylation, and natural selection in colorectal carcinogenesis

Neoplastic transformation is increasingly understood in terms of evolutionary mechanisms, and it is now widely accepted that tumor progression involves natural selection of genetic variants occurring in the somatic environment. Here we give a review of data that substantiate this Darwinian view to tumorigenesis, with particular emphasis on recent advances related to colorectal cancer. We specifically focus on the controversies related to genomic instability and DNA methylation, and present a model, which interrelates these phenomena to the basic evolutionary concept of biology.

Microsatellite instability and loss of heterozygosity in prostatic carcinomas: comparison of primary tumors, and of corresponding recurrences after androgen-deprivation therapy and lymph-node metastases

BACKGROUND

The molecular mechanisms leading to prostate cancer progression are poorly understood. In particular, those changes which are responsible for androgen-independent growth and metastatic spread in prostate cancer are an issue of current investigations.

METHODS

To gain more insight into these processes, paired microdissected samples from both untreated, locally advanced primary tumors (n = 20) and recurrences (n = 20) after conventional androgen-deprivation therapy (ADT) were analyzed retrospectively for microsatellite instability (MSI) and loss of heterozygosity (LOH) at nine loci on chromosomes 8, 18, and X by polymerase chain reaction. In parallel, 12 prostatic carcinomas treated by radical prostatectomy and nine corresponding lymph-node metastases were analyzed in the same way.

RESULTS

The group treated with ADT showed a total of 10 MSI in 7 of the primary tumors (35%): 4 of these (20%) at one locus, and 3 of these (15%) at two loci. In the recurrences, MSI was observed in 4 cases (20%): 3 of these at one locus (15%), and 1 of these (5%) at two loci. LOH was found in 8 cases (40%) before as well as after ADT. In the radically resected carcinomas, MSI could be detected at two chromosomal loci in one of the primary tumors (8%) and in one of the metastases (11%); LOH was found in 2 primaries (16%) and 3 metastases (33%).

CONCLUSIONS

Although MSI can be found in advanced prostatic carcinomas, it apparently does not play a major role in the progression of prostate cancer regarding androgen-independent growth or lymphogenous spread.

Microsatellite instability is infrequent in azoxymethane-induced rat intestinal tumors: An assessment by capillary electrophoresis

A rat model of colon cancer in which tumors are induced by azoxymethane (AOM) is frequently used to study putative environmental agents that may modify the risk of human colon cancer development. In order to evaluate the usefulness of this model for human risk assessment, a comparison of the molecular changes associated with tumorigenesis in the rat model with those in human colon cancer is desirable. Microsatellite instability (MSI), an alteration in length of short repetitive DNA sequences associated with defective DNA mismatch repair, is an important molecular characteristic of many human colon tumors. Intestinal tumors were induced in male Fischer 344 rats injected with 15 mg/kg body wt AOM in four weekly doses. Thirteen intestinal tumors were examined for MSI at 10 different microsatellite loci, using a capillary electrophoresis (CE) method for accurate assessment of DNA length. This method was shown to have a resolution of 1 bp for a 140-bp PCR product and to be capable of detecting one mutant sequence within a background of 10 wild-type sequences. The CE method also readily distinguished a known MSI-positive human tumor sample from its matching control sample. Among the 13 rat intestinal tumors examined, only one had MSI, which was present at only a single locus. We conclude that, unlike sporadic human colon tumors in which 15-30% of tumors have MSI (usually at multiple loci), MSI is very rare in AOM-induced rat intestinal tumors.

Stability of microsatellites in myeloid neoplasias

Microsatellites are short, repeated DNA sequences that exist throughout the genome. Instability of these sequences, associated with defects in the DNA mismatch repair system, is the hallmark of hereditary non-polyposis colorectal cancer (HNPCC), and is also found in many sporadic cancers. Although many types of solid tumors exhibit this type of genetic instability, its involvement in hematologic cancers is less evident. We have investigated whether microstatellite instability (MSI) is involved in the transformation of myeloid cells to myelodysplastic syndrome (MDS) and/or acute myelogenous leukemia (AML). Both de novo and treatment-associated neoplasias were studied. Only one example of MSI was found in 48 patients, using a panel of 14 different microsatellite loci consisting of repeats of one to four base pairs. These results suggest that the genes responsible for MSI are not involved in the transformation of normal myeloid cells to MDS or AML.

Accumulated clonal genetic alterations in familial and sporadic colorectal carcinomas with widespread instability in microsatellite sequences

A subset of hereditary and sporadic colorectal carcinomas is defined by microsatellite instability (MSI), but the spectra of gene mutations have not been characterized extensively. Thirty-nine hereditary nonpolyposis colorectal cancer syndrome carcinomas (HNPCCa) and 57 sporadic right-sided colonic carcinomas (SRSCCa) were evaluated. Of HNPCCa, 95% (37/39) were MSI-positive as contrasted with 31% (18/57) of SRSCCa (P < 0.000001), but instability tended to be more widespread in SRSCCa (P = 0.08). Absence of nuclear hMSH2 mismatch repair gene product by immunohistochemistry was associated with germline hMSH2 mutation (P = 0.0007). The prevalence of K-ras proto-oncogene mutations was similar in HNPCCa and SRSCCa (30% (11/37) and 30% (16/54)), but no HNPCCa from patients with germline hMSH2 mutation had codon 13 mutation (P = 0.02), and two other HNPCCa had multiple K-ras mutations attributable to subclones. 18q allelic deletion and p53 gene product overexpression were inversely related to MSI (P = 0.0004 and P = 0.0001, respectively). Frameshift mutation of the transforming growth factor beta type II receptor gene was frequent in all MSI-positive cancers (85%, 46/54), but mutation of the E2F-4 transcription factor gene was more common in HNPCCa of patients with germline hMSH2 mutation than in those with germline bMLH1 mutation (100% (8/8) versus 40% (2/5), P = 0.04), and mutation of the Bax proapoptotic gene was more frequent in HNPCCa than in MSI-positive SRSCCa (55% (17/31) versus 13% (2/15), P = 0.01). The most common combination of mutations occurred in only 23% (8/35) of evaluable MSI-positive cancers. Our findings suggest that the accumulation of specific genetic alterations in MSI-positive colorectal cancers is markedly heterogeneous, because the occurrence of some mutations (eg, ras, E2F-4, and Bax genes), but not others (eg, transforming growth factor beta type II receptor gene), depends on the underlying basis of the mismatch repair deficiency. This genetic heterogeneity may contribute to the heterogeneous clinical and pathological features of MSI-positive cancers.

Urinary tract cancer and hereditary nonpolyposis colorectal cancer: risks and screening options

PURPOSE

We investigate the risk of the different types of urinary tract cancer in hereditary nonpolyposis colorectal cancer families and review screening options.

MATERIALS AND METHODS

We retrospectively calculated the relative and cumulative risks of developing urinary tract cancer by comparing tumor occurrence in patients and their first degree relatives in the Dutch hereditary nonpolyposis colorectal cancer registry with those in the general Dutch population. A person-year analysis was used, including data on 1,321 individuals from 50 hereditary nonpolyposis colorectal cancer families.

RESULTS

The relative risk of developing transitional cell cancer of the renal pelvis or ureter was 14.04 (95% confidence interval 6.69 to 29.45, p <0.05) and the cumulative risk was 2.6%. The risks of renal (excluding renal pelvis) and bladder cancers were not significantly increased. Urinary tract cancer was diagnosed at a relatively young age and many women were affected. Some familial clustering was observed.

CONCLUSIONS

Our findings indicate that hereditary nonpolyposis colorectal cancer is associated with an increased risk of transitional cell cancer of the upper urinary tract. The cumulative risk is relatively low, although a subset of hereditary nonpolyposis colorectal cancer families may be exposed to a much higher risk. As yet nothing is known of the clinical impact of screening for urinary tract cancer in cases of hereditary nonpolyposis colorectal cancer. In a research setting screening by excretory urography of hereditary nonpolyposis colorectal cancer families with a strong history of upper urinary tract cancer should be considered.

Allelic imbalance and cytogenetic deletion of 1p in colorectal adenomas: a target region identified between DIS199 and DIS234

Both cytogenetic and molecular genetic analyses have shown that many colorectal adenomas carry an acquired deletion distally in the short arm of one chromosome 1, but the two methods have never been brought to bear on the same tumors. The major part of this study was the analysis of 53 previously short-term cultured and karyotyped colorectal adenomas for allelic imbalance at eight microsatellite loci in 1p. Allelic imbalances were detected in seven of the 12 adenomas that had cytogenetically visible abnormalities of chromosome 1, as well as in four adenomas that either had a normal karyotype (one case) or had clonal chromosome abnormalities that did not seem to involve chromosome 1 (three cases); i.e., 30% of the adenomas had abnormalities involving 1p by the combined approach. A minimal region of overlap seemed to map to between DIS199 and DIS234, suggesting that this is a relevant target region. This genomic area contains the human homologue of the tumor modifier gene Mom1 (1p35-36.1), which, in mice, modifies the number of intestinal tumors in multiple intestinal neoplasia (Min)-mutated animals. To evaluate whether the imbalances corresponded to interstitial deletions of 1p material, we performed fluorescence in situ hybridization with a pericentromeric probe (15 adenomas) and a telomeric probe (6 adenomas) on uncultured cells from the 16 adenomas with chromosome 1 abnormalities. Except for three adenomas that had already been shown by banding analysis to have a trisomic pattern, two centromere 1 signals were invariably found. In the cases hybridized with the 1p-telomeric probe, we found the same frequencies of telomeric and centromeric signals, in agreement with the interpretation that the deletions were interstitial. One of the 53 adenomas had genomic instability, seen as new alleles at five of eight microsatellite loci. A comparison of the genetic findings with clinicopathologic data indicated that adenomas in the rectum have 1p abnormalities more often than do adenomas of the sigmoid colon, and that adenomas with 1p changes are larger than adenomas without abnormalities of chromosome 1.

Different genetic pathways to proximal and distal colorectal cancer influenced by sex-related factors

Mutations in the k-ras and TP53 genes, as well as microsatellite instability (MIN), are frequent genetic alterations in colorectal carcinomas and represent 3 different mechanisms in the carcinogenic process. Both the incidence of colorectal cancer and the frequency of genetic alterations in such tumours have been related to different clinico-pathological variables, including age and gender of the patient and location of the tumour. A number of studies have also reported associations between different types of genetic alterations. We therefore wanted to explore the relationship between these genetic and clinico-pathological variables using multivariate analysis on material from 282 colorectal carcinomas. Three logistic regression models were constructed: 1) the presence of K-ras mutations was dependent on MIN and age and gender of patient, with an especially low frequency among younger males and in tumours with MIN (overall p = 0.0003); 2) the presence of TP53 mutations was only dependent on tumour location, with a positive association to cancers occurring distally (p = 0.002); and 3) the presence of MIN was dependent on age, gender and K-ras and TP53 mutations, as well as on tumour location. MIN was most frequent among younger male and older female patients, was rare in tumours with K-ras or TP53 mutations and was found almost exclusively in the proximal colon (overall p < 0.0001). Our data confirm that different genetic pathways to colorectal cancer dominate in the proximal and distal segments of the bowel and suggest that the K-ras- and MIN-dependent pathways are influenced by different sex-related factors.

How cancer gene testing can benefit patients

A revolution has taken place in the past few decades in our understanding of the genetic origins of human cancer. In particular, genes implicated in inherited susceptibility to forms of cancer are increasingly being identified and their mutations characterized. Many of these genes are also involved in sporadic tumours of the same type, as well as additional tumour types. Understanding of these genes will therefore affect an even greater number of patients.