Genes involved in DNA repair are mutational targets in endometrial cancers with microsatellite instability

Microsatellite instability (MSI) is observed in a subset of endometrial cancers (ECs) and is attributed to defects in mismatch repair. Mismatch repair deficiency allows for accumulation of mutations in the coding repeats of key target genes, which may be involved in the initiation and progression of MSI+ EC. We examined genes implicated in DNA repair pathways in 38 MSI-high (MSI-H), 10 MSI-low, 25 microsatellite stable ECs, and a selected panel of associated premalignant hyperplasias. Genetic alterations were correlated to histopathological data, including tumor grade and stage. Somatic frameshift mutations were observed in hMLH3, hMSH3, hMSH6, CHK1, and BAX genes in MSI-H endometrial hyperplasias and cancers, whereas mutations in ATR and CDC25C were observed only in MSI-H ECs. Increased mutation frequency in DNA damage response pathway genes including ATR, CHK1, and BAX demonstrated a significant trend with advancing tumor grade (P < 0.05). Our observations of the same mutations at short coding mononucleotide repeats in both premalignant lesions and tumors and association of increased frequency of mutation accumulation with advancing tumor grade suggest that these alterations may play a role in the development and progression of MSI+ EC.

Methylation of adenomatous polyposis coli in endometrial cancer occurs more frequently in tumors with microsatellite instability phenotype

Differential methylation is an important epigenetic control mechanism, which has been implicated in the development of a variety of cancers. Methylation of promoter regions of normally unmethylated tumor suppressor genes leads to transcriptional inactivation and ultimately to tumor formation. We hypothesized that epigenetic inactivation of adenomatous polyposis coli (APC), a key player in the suppressor pathway, may contribute to the development of endometrial cancer. We investigated APC methylation in endometrial adenocarcinoma specimens obtained from a series of patients (n = 114) and compared methylation profiles with microsatellite instability (MSI+) status. DNA microdissected from formalin-fixed, paraffin-embedded matched normal and tumor specimens, and a subset of associated endometrial hyperplasia was subjected to methylation-specific PCR of the APC promoter 1A region. Tumor-specific hypermethylation of APC with corresponding unmethylated normal endometrial tissue occurred in 43% (17 of 40) of MSI+ cases (P = 0.0007) and 16% (12 of 74) of microsatellite stable cases (P = 0.04). Interestingly, tumor tissue was unmethylated with normal tissue displaying APC methylation in 4% (5 of 114, 2MSI+ and 3 microsatellite stable) of cases. Endometrial cell lines AN3CA, RL95-2, and HEC-1B all displayed exclusive methylation of promoter 1A, and treatment of the AN3CA cell line with the demethylating agent 5-aza-2'-deoxycytidine exhibited re-expression of APC as confirmed by RT-PCR analysis. Our results demonstrate APC methylation in endometrial cancer for the first time and show that APC hypermethylation occurs at an increased frequency in MSI+ endometrial tumors (P = 0.01).

An MLH1 haplotype is over-represented on chromosomes carrying an HNPCC predisposing mutation in MLH1

BACKGROUND

The mismatch repair gene, MLH1, appears to occur as two main haplotypes at least in white populations. These are referred to as A and G types with reference to the A/G polymorphism at IVS14-19. On the basis of preliminary experimental data, we hypothesised that deviations from the expected frequency of these two haplotypes could exist in carriers of disease associated MLH1 germline mutations.

METHODS

We assembled a series (n=119) of germline MLH1 mutation carriers in whom phase between the haplotype and the mutation had been conclusively established. Controls, without cancer, were obtained from each contributing centre. Cases and controls were genotyped for the polymorphism in IVS14.

RESULTS

Overall, 66 of 119 MLH1 mutations occurred on a G haplotype (55.5%), compared with 315 G haplotypes on 804 control chromosomes (39.2%, p=0.001). The odds ratio (OR) of a mutation occurring on a G rather than an A haplotype was 1.93 (95% CI 1.29 to 2.91). When we compared the haplotype frequencies in mutation bearing chromosomes carried by people of different nationalities with those seen in pooled controls, all groups showed a ratio of A/G haplotypes that was skewed towards G, except the Dutch group. On further analysis of the type of each mutation, it was notable that, compared with control frequencies, deletion and substitution mutations were preferentially represented on the G haplotype (p=0.003 and 0.005, respectively).

CONCLUSION

We have found that disease associated mutations in MLH1 appear to occur more often on one of only two known ancient haplotypes. The underlying reason for this observation is obscure, but it is tempting to suggest a possible role of either distant regulatory sequences or of chromatin structure influencing access to DNA sequence. Alternatively, differential behaviour of otherwise similar haplotypes should be considered as prime areas for further study.

Immunohistochemistry versus microsatellite instability testing in phenotyping colorectal tumors

PURPOSE

To compare microsatellite instability (MSI) testing with immunohistochemical (IHC) detection of hMLH1 and hMSH2 in colorectal cancer.

PATIENTS AND METHODS

Colorectal cancers from 1,144 patients were assessed for DNA mismatch repair deficiency by two methods: MSI testing and IHC detection of hMLH1 and hMSH2 gene products. High-frequency MSI (MSI-H) was defined as more than 30% instability of at least five markers; low-level MSI (MSI-L) was defined as 1% to 29% of loci unstable.

RESULTS

Of 1,144 tumors tested, 818 showed intact expression of hMLH1 and hMSH2. Of these, 680 were microsatellite stable (MSS), 27 were MSI-H, and 111 were MSI-L. In all, 228 tumors showed absence of hMLH1 expression and 98 showed absence of hMSH2 expression: all were MSI-H.

CONCLUSION

IHC in colorectal tumors for protein products hMLH1 and hMSH2 provides a rapid, cost-effective, sensitive (92.3%), and extremely specific (100%) method for screening for DNA mismatch repair defects. The predictive value of normal IHC for an MSS/MSI-L phenotype was 96.7%, and the predictive value of abnormal IHC was 100% for an MSI-H phenotype. Testing strategies must take into account acceptability of missing some cases of MSI-H tumors if only IHC is performed.

Considerations when analyzing the methylation status of PTEN tumor suppressor gene

Epigenetic mechanisms of gene silencing, including promoter hypermethylation of tumor suppressor genes, have been shown to contribute to tumorigenesis. PTEN is an important tumor suppressor implicated in the pathogenesis of a number of familial and sporadic cancers. Germline mutations of PTEN predispose to dominantly inherited hamartomatous disorders Cowden syndrome and Bannayan-Zonana syndrome. Somatic PTEN mutations commonly occur in endometrial, breast, prostate, and thyroid tumors. Several investigators have speculated on PTEN promoter hypermethylation as a possible mechanism of PTEN inactivation but data supporting such observations is not forthcoming. The genomic sequence of PTEN is 98% identical to a highly conserved processed PTEN pseudogene (psiPTEN) and this sequence identity extends 841 base pairs into the promoter region. This high degree of homology has made analysis of the methylation status of the PTEN promoter quite challenging. We have investigated the methylation profiles of the promoter region of PTEN in endometrial, breast, and colon cancer cell lines, as well as in a panel of primary endometrial tumors using a combination of methylation-specific polymerase chain reaction, methylation-sensitive restriction analysis, and bisulfite sequencing. Our results show that the pseudogene, and not PTEN, is predominantly methylated in cell lines and tumors. Without careful consideration of the critical nucleotide differences between the two sequences, results obtained from PTEN analysis may not necessarily represent the methylation status of PTEN.

Immunohistochemistry versus microsatellite instability testing in phenotyping colorectal tumors

PURPOSE

To compare microsatellite instability (MSI) testing with immunohistochemical (IHC) detection of hMLH1 and hMSH2 in colorectal cancer.

PATIENTS AND METHODS

Colorectal cancers from 1,144 patients were assessed for DNA mismatch repair deficiency by two methods: MSI testing and IHC detection of hMLH1 and hMSH2 gene products. High-frequency MSI (MSI-H) was defined as more than 30% instability of at least five markers; low-level MSI (MSI-L) was defined as 1% to 29% of loci unstable.

RESULTS

Of 1,144 tumors tested, 818 showed intact expression of hMLH1 and hMSH2. Of these, 680 were microsatellite stable (MSS), 27 were MSI-H, and 111 were MSI-L. In all, 228 tumors showed absence of hMLH1 expression and 98 showed absence of hMSH2 expression: all were MSI-H.

CONCLUSION

IHC in colorectal tumors for protein products hMLH1 and hMSH2 provides a rapid, cost-effective, sensitive (92.3%), and extremely specific (100%) method for screening for DNA mismatch repair defects. The predictive value of normal IHC for an MSS/MSI-L phenotype was 96.7%, and the predictive value of abnormal IHC was 100% for an MSI-H phenotype. Testing strategies must take into account acceptability of missing some cases of MSI-H tumors if only IHC is performed.

Motivations and psychosocial impact of genetic testing for HNPCC

A type of hereditary colorectal cancer (CRC) known as hereditary nonpolyposis colorectal cancer (HNPCC) is associated with MLHI and MSH2 gene mutations. This study consists of a pilot, cross-sectional study of 50 individuals who were engaged in the genetic testing process for HNPCC. The study investigated the motivations and attitudes around genetic testing and current psychosocial functioning through the use of standardized measures, as well as obtained information on disclosure patterns associated with test results. The mean age of the sample was 44.3 years. (SD = 15.0). Twenty-three individuals were identified as "carriers" (13 had a previous history of CRC), seven were "non-carriers" and 20 individuals were still awaiting test results. The primary motivations for participating in genetic testing were similar to previous reports and included: wanting to know if more screening tests were needed, obtaining information about the risk for offspring and increasing certainty around their own risk. The psychosocial scores demonstrated that a subgroup of individuals exhibited distress, with greater distress for those individuals awaiting results or testing positive. There was a high level of satisfaction associated with the experience of testing. Individuals in this study tended to disclose their test results to a variety of family and non-family members. Disclosure was primarily associated with positive experiences however, some individuals reported regret around disclosure of their results. These preliminary findings should be further explored in a larger prospective study design over multiple time points.

Do MSH6 mutations contribute to double primary cancers of the colorectum and endometrium?

Mismatch repair (MMR) gene mutations cause hereditary nonpolyposis colorectal cancer (HNPCC), a common form of familial colorectal cancer. Among MMR genes, germline MSH6 mutations are often observed in HNPCC-like families with an increased frequency of endometrial cancer. We have previously shown that a proportion of women affected with double primary cancers of the colorectum and endometrium carry germline MSH2 or MLH1 mutations and, thus, belong to HNPCC families. In this study, we have investigated the specific contribution of MSH6 defects to such double primary patients. By sequence analysis of the entire coding region of MSH6, three putative missense mutations were identified in patients with atypical family histories that do not meet HNPCC criteria. Moreover, one of these mutations, a novel substitution Arg901 His, was found in a patient previously shown to carry a truncating germline MLH1 mutation. Thus, MSH6 mutations are likely to contribute to the etiology of double primary cancers of the colorectum and endometrium.

Human microphthalmia associated with mutations in the retinal homeobox gene CHX10

Isolated human microphthalmia/anophthalmia, a cause of congenital blindness, is a clinically and genetically heterogeneous developmental disorder characterized by a small eye and other ocular abnormalities. Three microphthalmia/anophthalmia loci have been identified, and two others have been inferred by the co-segregation of translocations with the phenotype. We previously found that mice with ocular retardation (the or-J allele), a microphthalmia phenotype, have a null mutation in the retinal homeobox gene Chx10 (refs 7,8). We report here the mapping of a human microphthalmia locus on chromosome 14q24.3, the cloning of CHX10 at this locus and the identification of recessive CHX10 mutations in two families with non-syndromic microphthalmia (MIM 251600), cataracts and severe abnormalities of the iris. In affected individuals, a highly conserved arginine residue in the DNA-recognition helix of the homeodomain is replaced by glutamine or proline (R200Q and R200P, respectively). Identification of the CHX10 consensus DNA-binding sequence (TAATTAGC) allowed us to demonstrate that both mutations severely disrupt CHX10 function. Human CHX10 is expressed in progenitor cells of the developing neuroretina and in the inner nuclear layer of the mature retina. The strong conservation in vertebrates of the CHX10 sequence, pattern of expression and loss-of-function phenotypes demonstrates the evolutionary importance of the genetic network through which this gene regulates eye development.

A germline mutation at the extreme 3' end of the APC gene results in a severe desmoid phenotype and is associated with overexpression of beta-catenin in the desmoid tumor

Desmoid tumors arise sporadically or as part of the extraintestinal manifestations of familial adenomatous polyposis (FAP). In FAP, two distinct clinical presentations of the desmoid phenotype are seen: 1) one or a few desmoid tumors present predominantly in the abdominal wall or the abdomen; 2) a florid proliferation of tumors early in life, mostly near the axial skeleton or extremities. These different phenotypes have been associated with different sites of germline mutations in the adenomatous polyposis coli gene (APC gene). We present a large, French-Canadian kindred with a florid desmoid tumor phenotype caused by a germline mutation at codon 2643-2644 of the APC gene. The phenotype was characterized by the early onset of multiple tumors, arising near the axial skeleton and in proximal extremities. The penetrance of desmoid tumors was near 100% in this kindred. However, the expression of the disease was variable amongst the different affected relatives. Many gene carriers had cutaneous cysts. Polyposis of the colon was rarely observed in the affected individuals and we did not document upper gastro-intestinal polyps. The mutant APC allele did not express a stable truncated protein in vivo. Molecular analysis of the proband's tumor DNA revealed a somatic inactivating mutation of the wild-type allele. Immunohistochemistry on the tumor also demonstrated elevated levels of beta-catenin. The present study demonstrates that this extreme 3' APC mutation is associated with a severely penetrant desmoid phenotype and attenuated polyposis coli. It also suggests the involvement of the beta-catenin pathway in the development of desmoid tumors in FAP. The natural history of the disease is variable between individuals, and surgical interventions have to be timed appropriately due to the frequent recurrences.

Predominance of beta-catenin mutations and beta-catenin dysregulation in sporadic aggressive fibromatosis (desmoid tumor)

Aggressive fibromatosis (also called desmoid tumor) occurs as a sporadic lesion or as part of Familial Adenomatous Polyposis, which is caused by germ line mutations in the Adenomatous polyposis Coli (APC) gene. APC is involved in the regulation of the cellular level of beta-catenin, which is a mediator in Wnt signaling. Mutational analysis of the beta-catenin and APC genes was performed in 42 sporadic aggressive fibromatoses. Nine tumors had mutations in APC, and 22 had a point mutation in beta-catenin at either codon 45 or codon 41 (producing a stabilized beta-catenin protein product). Immunohistochemistry showed an elevated beta-catenin protein level in all tumors, regardless of mutational status. Beta-catenin localized to the nucleus, and was not tyrosine phosphorylated in the six tumors in which this was tested. The demonstration of mutations in two mediators in the Wnt-APC-beta-catenin pathway implicates beta-catenin stabilization as the key factor in the pathogenesis of aggressive fibromatosis. This is the first demonstration of somatic beta-catenin mutations in a locally invasive, but non metastatic lesion composed of spindle cells, illustrating the importance of beta-catenin stabilization in a variety of cell types and neoplastic processes. Moreover, this tumor has one of the highest reported frequencies of beta-catenin mutations of any tumor type.

STK11/LKB1 germline mutations are not identified in most Peutz-Jeghers syndrome patients

Germline mutations of the STK11 gene mapped to chromosome 19p13.3 are responsible for Peutz Jeghers syndrome (PJS), a dominant disorder associated with characteristic gastrointestinal hamartomatous polyps and a predisposition to various cancers. We conducted a detailed investigation of germline STK11 alterations by protein truncation test and genomic DNA sequence analysis in ten unrelated PJS families. We identified a novel truncating deletion spanning STK11 exons 2-7 in a single patient and several known polymorphisms. Loss of heterozygosity studies in PJS polyps of four of these patients identified an allelic deletion of D19S886 in another patient. Our results suggest that STK11 mutations account for only a proportion of PJS cases.

Beta-catenin mutations are specific for colorectal carcinomas with microsatellite instability but occur in endometrial carcinomas irrespective of mutator pathway

Some colorectal tumors with wild-type adenomatous polyposis coli gene have activating mutations in beta-catenin (encoded by CTNNB1) that result in decreased phosphorylation by GSK-3beta and increased signaling through the Tcf/Lef transcription factors. To investigate the relationship between CTNNB1 mutations and underlying pathways of genomic instability, we examined 80 colorectal cancers stratified by the presence or absence of microsatellite instability (MSI). CTNNB1 mutations were identified in 13 (25%) of 53 cancers with high frequency MSI (MSI-H), including 12 point mutations at exon 3 phosphorylation sites (codons 41 and 45) and one deletion of the entire exon 3 degradation box. No CTNNB1 mutations were identified in 27 microsatellite stable or low frequency MSI (MSI-L) colorectal cancers (P < 0.01). In contrast, CTNNB1 mutations were identified in 3 of 9 (33%) MSI-H and 10 of 20 (50%) MSS/MSI-L endometrial carcinomas, suggesting a more generalized involvement in these tumors. Only six (46%) of the endometrial carcinoma CTNNB1 mutations occurred at residues directly phosphorylated by GSK-3beta, and only one of these was at either codon 41 or 45. All point mutations in MSI-H cancers were transitions, whereas 64% of those in MSS/MSI-L cancers were transversions (P < 0.01). The differences in the mutation profiles suggest that there may be molecular fingerprints of CTNNB1 mutations, determined by biological factors related to both tumor type and underlying pathways of genomic instability.

Cost comparison of predictive genetic testing versus conventional clinical screening for familial adenomatous polyposis

BACKGROUND

Mutations of the APC gene cause familial adenomatous polyposis (FAP), a hereditary colorectal cancer predisposition syndrome.

AIMS

To conduct a cost comparison analysis of predictive genetic testing versus conventional clinical screening for individuals at risk of inheriting FAP, using the perspective of a third party payer.

METHODS

All direct health care costs for both screening strategies were measured according to time and motion, and the expected costs evaluated using a decision analysis model.

RESULTS

The baseline analysis predicted that screening a prototype FAP family would cost $4975/ pound3109 by molecular testing and $8031/ pound5019 by clinical screening strategy, when family members were monitored with the same frequency of clinical surveillance (every two to three years). Sensitivity analyses revealed that the genetic testing approach is cost saving for key variables including the kindred size, the age of screening onset, and the cost of mutation identification in a proband. However, if the APC mutation carriers were monitored at an increased (annual) frequency, the cost of the genetic screening strategy increased to $7483/ pound4677 and was especially sensitive to variability in age of onset of screening, family size, and cost of genetic testing of at risk relatives.

CONCLUSIONS

In FAP kindreds, a predictive genetic testing strategy costs less than conventional clinical screening, provided that the frequency of surveillance is identical using either strategy. An additional significant benefit is the elimination of unnecessary colonic examinations for those family members found to be non-carriers.

Mismatch repair gene defects contribute to the genetic basis of double primary cancers of the colorectum and endometrium

Hereditary non-polyposis colorectal cancer (HNPCC) is a dominantly inherited cancer syndrome caused by germline defects of mismatch repair (MMR) genes. Endometrial cancer is the most common extracolonic neoplasm in HNPCC and is the primary clinical manifestation of the syndrome in some families. The cumulative incidence of endometrial cancer among HNPCC mutation carriers is high, estimated to be from 22 to 43%. We hypothesized that women with double primary cancers of the colorectum and endometrium are likely to be members of HNPCC families. In order to determine how frequently HNPCC manifests in the context of double primary cancers, we examined alterations of two MMR genes, hMSH2 and hMLH1, in 40 unrelated women affected with double primary cancers. These cases were identified using hospital-based and population-based cancer registries in Ontario, Canada. MMR gene mutations were screened by single-strand conformation polymorphism analysis and confirmed by direct sequencing. Eighteen percent (seven of 40) were found to harbor mutations of one of the two MMR genes. Analysis of colorectal and/or endometrial tumors of mutation-negative probands found microsatellite instability in seven of 20 cases. Six of seven mutation-positive probands had strong family histories suggestive of HNPCC. First degree relatives of mutation-positive probands had a very high relative risk (RR) of colorectal cancer (RR = 8.1, CI 3. 5-15.9) and endometrial cancer (RR = 23.8, CI 6.4-61.0). The relative risk of mutation-negative cases was 2.8 (CI 1.7-4.5) for colorectal cancer and 5.4 (CI 2.0-11.7) for endometrial cancer. We recommend that all double primary patients with cancers at these sites should have a genetic evaluation, including molecular analysis for HNPCC where appropriate.

Negative genetic test result in familial adenomatous polyposis: clinical screening implications

PURPOSE

The goal of genetic testing is to define individual risk, which in turn may guide clinical management.

METHODS

Thirty-two international familial adenomatous polyposis registries were surveyed regarding their approach to a specific clinical management question. There were 30 respondents. Respondents declared their clinical policy for an at-risk, first-degree relative who undergoes direct mutation analysis and does not have an APC gene mutation known to be present in his or her family.

RESULTS

Nineteen of 30 (63.3 percent) registries would discharge this negative APC mutation case from clinical screening. Eleven of 30 (37 percent) registries would maintain clinical screening. Reasons offered for maintaining surveillance included the need for additional confirmation of the APC mutation in two affected relatives, the possibility of sampling error or two different mutations in an affected family, limited prospective data, and patient anxiety.

CONCLUSIONS

The discrepancy in response to the survey suggests that some clinicians are as yet reluctant to accept fully that predictive genetic analysis is a definitive guide to clinical management in familial adenomatous polyposis. Nevertheless, we believe that use of a predictive gene test for familial adenomatous polyposis should alter management, decrease cost, and reduce psychological trauma for the tested individual. Although the benefit of APC analysis is accepted for the positive gene carrier, the challenge remains to reclassify the negative gene carriers who are no longer at risk for familial adenomatous polyposis.

Distinct regions of frequent loss of heterozygosity of chromosome 5p and 5q in human esophageal cancer

Loss of heterozygosity (LOH) studies reported thus far suggest that tumor suppressor loci on chromosome 5q are important in esophageal cancer (EC) while little is known about the involvement of chromosome 5p. To investigate the potential existence of tumor suppressor gene(s) on chromosome 5 contributing to the development of EC, we performed LOH studies using a total of 24 polymorphic markers spanning the entire chromosome 5. Seventy primary esophageal cancers were microdissected and allelic deletions were detected by polymerase chain reaction (PCR)-single strand conformation polymorphism or by microsatellite analysis. LOH was observed in at least 1 of the loci in 47 of 70 (67%) esophageal tumors. Initially, 40 tumors [24 squamous cell carcinomas (SCC) and 16 adenocarcinomas (ADC)], each with matched histologically normal esophageal mucosa, were analyzed at 15 marker loci on 5p and 5q. A novel locus, D5S667 on 5p15.2, exhibited the highest frequency of LOH (44%) in these tumors along with another previously reported region of frequent deletion, irf-1 (5q31.1). In a series of 30 additional EC tumors (11 SCC and 19 ADC), a detailed LOH analysis of chromosome 5p15.2 region was conducted using 10 additional polymorphic markers, which mapped the frequently deleted region within 1 cM. Overall, LOH at the D5S667 locus was observed more frequently in SCC than in ADC (62% vs. 23%, p = 0.01). This significant rate of LOH of a distinct region of chromosome 5p implicates the existence of a putative tumor suppressor gene locus involved in EC.

Adenomatous polyposis coli gene mutation alters proliferation through its beta-catenin-regulatory function in aggressive fibromatosis (desmoid tumor)

Aggressive fibromatosis is a monoclonal proliferation of spindle (fibroblast-like) cells. A subset of lesions contain somatic truncating adenomatous polyposis coli (APC) gene mutations, and all of the lesions contain an elevated beta-catenin protein level. A major function of APC is to regulate beta-catenin protein level. Beta-catenin has a dual function in the cell: it is a member of the adherens junction, and it binds transcription factors in the tcf-lef family, transactivating transcription. Cell cultures from aggressive fibromatoses containing an APC mutation were studied. Transient transfection of the full-length APC gene caused decreased proliferation and beta-catenin protein level in these cultures. To determine whether beta-catenin protein level was responsible for the change in proliferation rate, stable transfections of deltaN89beta-catenin (a stabilized form that is not degraded by APC, but retains all other functions) were achieved in half of the cultures derived from each tumor, whereas the other half were transfected with an empty vector. Transfection of the full-length APC gene in cultures that were stably transfected with deltaN89beta-catenin did not result in a change in proliferation. The type I promotor of p56lck contains an HMG consensus region, to which members of the tcf-lef family can bind. p56lck was expressed in cultures not transfected with the full-length APC gene and in cultures transfected with the full-length APC gene and deltaN89beta-catenin, but not in cultures transfected with only the full-length APC gene. These data show that APC truncating mutations give aggressive fibromatosis cells a proliferative advantage through beta-catenin and suggest that beta-catenin acts to transactivate transcription.

Genotype-phenotype correlations in attenuated adenomatous polyposis coli

Germ-line mutations of the tumor suppressor APC are implicated in attenuated adenomatous polyposis coli (AAPC), a variant of familial adenomatous polyposis (FAP). AAPC is recognized by the occurrence of <100 colonic adenomas and a later onset of colorectal cancer (age >40 years). The aim of this study was to assess genotype-phenotype correlations in AAPC families. By protein-truncation test (PTT) assay, the entire coding region of the APC gene was screened in affected individuals from 11 AAPC kindreds, and their phenotypic differences were examined. Five novel germ-line APC mutations were identified in seven kindreds. Mutations were located in three different regions of the APC gene: (1) at the 5' end spanning exons 4 and 5, (2) within exon 9, and (3) at the 3' distal end of the gene. Variability in the number of colorectal adenomas was most apparent in individuals with mutations in region 1, and upper-gastrointestinal manifestations were more severe in them. In individuals with mutations in either region 2 or region 3, the average number of adenomas tended to be lower than those in individuals with mutations in region 1, although age at diagnosis was similar. In all AAPC kindreds, a predominance of right-sided colorectal adenomas and rectal polyp sparing was observed. No desmoid tumors were found in these kindreds. Our data suggest that, in AAPC families, the location of the APC mutation may partially predict specific phenotypic expression. This should help in the design of tailored clinical-management protocols in this subset of FAP patients.

Overexpression of the nonpancreatic secretory group II PLA2 messenger RNA and protein in colorectal adenomas from familial adenomatous polyposis patients

The synovial fluid or group II secretory phospholipase A2 (sPLA2) has been implicated in various inflammatory processes and has been shown to release arachidonic acid for prostaglandin biosynthesis. In human colorectal cancer, both arachidonic acid and eicosanoid levels are elevated. Recently, sPLA2 has been identified as a candidate gene that modifies the Apc gene in the Min mouse, a murine model for familial adenomatous polyposis (FAP). Loss of sPLA2 gene function results in susceptibility to the Min phenotype and the formation of multiple intestinal polyps, whereas mice expressing an active sPLA2 gene are resistant to polyp formation. Therefore, there are two potentially contrasting roles for sPLA2 in colon cancer; one is protection against polyp formation, and the other, the release of arachidonic acid for prostaglandin production and subsequent tumor promotion. To investigate these contrasting dual roles of sPLA2, we have examined the expression and sequence of the sPLA2 mRNA in normal mucosa and duodenal and colorectal polyps from FAP patients. In 11 of 14 patients, there was a significant increase in sPLA2 mRNA levels in the adenoma over the normal tissue. In some cases, there was over 100-fold increase in mRNA levels in the adenoma compared with normal tissue. Analysis of multiple adenomatous polyps from individual patients revealed that not all polyps contained elevated levels of sPLA2 mRNA. Immunoblot analysis also showed that sPLA2 protein expression was elevated in adenoma over normal tissue in five of six FAP patients analyzed. Furthermore, sequence analysis of sPLA2 mRNA present in these samples did not reveal mutations in the coding region. The implications of the up-regulation of sPLA2 in FAP is not clear, but unlike the Min mouse model, it does not seem to have a significant effect on polyp formation. In contrast, the high level of sPLA2 expression is more likely contributing to the elevated levels of arachidonic acid found in colorectal cancer and, in conjunction with the elevated expression of cyclooxygenase-2, could be another factor in tumor formation.

Molecular biology of colorectal cancer

Colorectal cancer is a significant cause of morbidity and mortality in Western populations. This cancer develops as a result of the pathologic transformation of normal colonic epithelium to an adenomatous polyp and ultimately an invasive cancer. The multistep progression requires years and possibly decades and is accompanied by a number of recently characterized genetic alterations. Mutations in two classes of genes, tumor-suppressor genes and proto-oncogenes, are thought to impart a proliferative advantage to cells and contribute to development of the malignant phenotype. Inactivating mutations of both copies (alleles) of the adenomatous polyposis coli (APC) gene--a tumor-suppressor gene on chromosome 5q--mark one of the earliest events in colorectal carcinogenesis. Germline mutation of the APC gene and subsequent somatic mutation of the second APC allele cause the inherited familial adenomatous polyposis syndrome. This syndrome is characterized by the presence of hundreds to thousands of colonic adenomatous polyps. If these polyps are left untreated, colorectal cancer develops. Mutation leading to dysregulation of the K-ras protooncogene is also thought to be an early event in colon cancer formation. Conversely, loss of heterozygosity on the long arm of chromosome 18 (18q) occurs later in the sequence of development from adenoma to carcinoma, and this mutation may predict poor prognosis. Loss of the 18q region is thought to contribute to inactivation of the DCC tumor-suppressor gene. More recent evidence suggests that other tumor-suppressor genes--DPC4 and MADR2 of the transforming growth factor beta (TGF-beta) pathway--also may be inactivated by allelic loss on chromosome 18q. In addition, mutation of the tumor-suppressor gene p53 on chromosome 17p appears to be a late phenomenon in colorectal carcinogenesis. This mutation may allow the growing tumor with multiple genetic alterations to evade cell cycle arrest and apoptosis. Neoplastic progression is probably accompanied by additional, undiscovered genetic events, which are indicated by allelic loss on chromosomes 1q, 4p, 6p, 8p, 9q, and 22q in 25% to 50% of colorectal cancers. Recently, a third class of genes, DNA repair genes, has been implicated in tumorigenesis of colorectal cancer. Study findings suggest that DNA mismatch repair deficiency, due to germline mutation of the hMSH2, hMLH1, hPMS1, or hPMS2 genes, contributes to development of hereditary nonpolyposis colorectal cancer. The majority of tumors in patients with this disease and 10% to 15% of sporadic colon cancers display microsatellite instability, also know as the replication error positive (RER+) phenotype. This molecular marker of DNA mismatch repair deficiency may predict improved patient survival. Mismatch repair deficiency is thought to lead to mutation and inactivation of the genes for type II TGF-beta receptor and insulin-like growth-factor II receptor. Individuals from families at high risk for colorectal cancer (hereditary nonpolyposis colorectal cancer or familial adenomatous polyposis) should be offered genetic counseling, predictive molecular testing, and when indicated, endoscopic surveillance at appropriate intervals. Recent studies have examined colorectal carcinogenesis in the light of other genetic processes. Telomerase activity is present in almost all cancers, including colorectal cancer, but rarely in benign lesions such as adenomatous polyps or normal tissues. Furthermore, genetic alterations that allow transformed colorectal epithelial cells to escape cell cycle arrest or apoptosis also have been recognized. In addition, hypomethylation or hypermethylation of DNA sequences may alter gene expression without nucleic acid mutation.

Familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC): a review of clinical, genetic and therapeutic aspects

Familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC) are two syndromes of colorectal cancer predisposition, inherited in an autosomal dominant fashion. They account for about 1% and 5-7% of all colorectal cancer cases, respectively. FAP is caused by germline mutations of a tumour suppressor gene, the adenomatous polyposis coli (APC) gene, whereas HNPCC results from genetic alterations of the DNA mismatch repair genes. Clinical manifestations in FAP include colonic as well as extracolonic sites (duodenum, eye, dental, nervous or connective tissues). In FAP, prophylactic colectomy is required in all affected patients and regular endoscopic check-up of the upper gastrointestinal tract is necessary to detect malignant transformation of duodenal polyps; medical management of complex desmoid tumours is preferred rather than surgery. In HNPCC, there are extracolonic associated endometrial, gastric, small bowel or brain carcinomas. At present time, for HNPCC patients, only preventive measures such as regular colonoscopic or gynecologic examinations are recommended, since prophylactic colectomy or hysterectomy are not considered to be routine procedures.

Using genetic information to make surgical decisions: report of a case of a 13-year-old boy with colon cancer

PURPOSE

We report the case of a boy aged 13 years who was diagnosed with a Dukes B obstructing cancer of the sigmoid colon. At the time of diagnosis, he underwent a Hartmann's procedure with end colostomy. Because of his unusually young age, he was referred to the Familial GI Cancer Registry at Mount Sinai Hospital for genetic assessment. A detailed pedigree revealed no significant history other than lung cancer in his maternal grandfather.

METHODS

We obtained his tumor specimen and performed molecular analysis of both normal colonic and tumor DNA. Specifically, we identified replication errors (RER) in the patient's tumor DNA when compared with normal colonic DNA. RER has been found in more than 90 percent of tumors from patients with Hereditary Nonpolyposis Colon Cancer (HNPCC) and is, thus, considered to be one of the hallmarks of this disease. Because HNPCC patients have a 40 percent risk of synchronous or metachronous tumors, the recommended surgery for HNPCC should be at least a subtotal colectomy with ileorectal anastomosis.

RESULTS

Based on molecular results, we were able to recommend that the patient have a subtotal colectomy performed instead of merely colostomy closure, to reduce his lifetime risk of developing further colon tumors and to make surveillance of the remaining rectum relatively easy. In this patient, we subsequently identified a germline mutation of the mismatch repair gene hMSH2 that is implicated in HNPCC. The possibility of HNPCC should be considered in adolescents who are diagnosed with colorectal cancer, so appropriate surgical decisions can be made.