Does early colectomy increase desmoid risk in familial adenomatous polyposis?

BACKGROUND & AIMS

Desmoid tumors are non-metastasizing fibromatoses that occur in 10%-20% of subjects with familial adenomatous polyposis (FAP). Intra-abdominal desmoid tumors are a major cause of mortality in FAP. FAP-associated desmoid tumors are linked to trauma, particularly abdominal surgery, family history of desmoids, hormonal factors, and the location of the APC mutation. We hypothesized that prophylactic colectomy at an early age might increase the risk of developing desmoids. The aim of this study was to determine whether colectomy earlier in life is a risk factor for the development of desmoid tumors.

METHODS

An analysis was made of the association between development of desmoid and age at colectomy, family history of desmoids, gender, and APC mutation in FAP patients in the Registry (1980-2005) at Mount Sinai Hospital, Toronto, Ontario, Canada.

RESULTS

FAP patients (n = 930) from 365 kindreds were identified. Desmoid prevalence was 14% (n = 121). Female patients were more likely to develop desmoids than male patients (17% vs 11%, P = .03). Female patients who had an early colectomy were more than 2 times more likely to develop a desmoid, compared with women who had a colectomy at >18 years (P = .01). Early colectomy did not increase risk of developing a desmoid in male patients (P = .42). Female patients who had an early colectomy (</=18 years) were 2.5 times more likely to develop desmoids, compared with male patients who had a late colectomy (P = .05). The prevalence of desmoids in the 5' and 3' groups was 13% and 38%, respectively (P = .0005). Patients with a mutation after codon 1399 were found to have 4 times greater chance of developing a desmoid.

CONCLUSIONS

Female patients with FAP are more likely to develop desmoids than male patients. Female patients who had an early colectomy are at significantly greater risk of developing a desmoid compared with female patients who had a colectomy in adulthood. Patients with APC mutations beyond codon 1399 are more likely to develop desmoids. These results suggest that delayed colectomy might be considered in young female patients with FAP to decrease the chances of developing desmoids.

Suppression of nuclear Wnt signaling leads to stabilization of Rac1 isoforms

The Rac1 GTPase contains a functional nuclear localization signal (NLS) and destruction box sequence in the C-terminal polybasic region. It has been postulated that these two regulatory sequences may function together, enabling Rac1 to participate in nuclear signaling pathways that ultimately target it for degradation. We have previously shown that the NLS activity of Rac1 and the Rac1b splice variant is essential for Wnt pathway activation. In the present study, we demonstrate that suppression of nuclear Wnt signaling leads to stabilization of Rac1 protein. In addition, we show that Rac1b may be under proteasomal regulation. We propose that Rac1 and Rac1b levels are regulated by being targeted for degradation through a negative feedback loop initiated by Wnt signaling.

Germline MYH mutations in a clinic-based series of Canadian multiple colorectal adenoma patients

OBJECTIVES

MYH is a member of the DNA base excision repair (BER) pathway and mutations of this gene predispose to the development of colorectal neoplasia in an autosomal recessive transmission pattern. Our objective was to determine the significance of MYH mutations in a series of Canadian patients with multiple adenomas.

METHODS

We screened for germline MYH mutations (by dHPLCO) in 20 clinic-based multiple adenoma patients who were adenomatous polyposis coli (APC) mutation-negative. Suspected mutations were confirmed by sequence analysis.

RESULTS

Six of 20 (30%) patients carried pathogenic biallelic MYH mutations, 1 Y165C homozygote and 5 compound heterozygotes of other sequence variants. We identified three novel variants, Q377X, 1314delA, and P281L, which are likely pathogenic. Twenty-nine relatives of the Y90X/1103delC compound heterozygous carrier were also screened for germline MYH mutations, and 1 homozygous and 14 heterozygous carriers were identified.

CONCLUSIONS

Among patients with multiple adenomas, biallelic MYH mutations account for approximately 30% of APC mutation negative cases and two thirds of these carry mutations other than the "common" Y165C and G382D variants. Clinical screening algorithms which focus only on the Y165C and G382D alleles are inadequate since additional pathogenic mutations may be identified by screening the entire gene.

MLH1 -93G>A promoter polymorphism and the risk of microsatellite-unstable colorectal cancer

BACKGROUND

Although up to 30% of patients with colorectal cancer have a positive family history of colorectal neoplasia, few colorectal cancers can be explained by mutations in high-penetrance genes. We investigated whether polymorphisms in DNA mismatch repair genes are associated with the risk of colorectal cancer.

METHODS

We genotyped 929 case patients and 1098 control subjects from Ontario and 430 case patients and 275 control subjects from Newfoundland and Labrador for five polymorphisms in the mismatch repair genes MLH1 and MSH2 with the fluorogenic 5' nuclease assay. Tumor microsatellite instability (MSI) was determined with a polymerase chain reaction-based method; MSI status was assigned as high (MSI-H, > or = 30% unstable markers among all markers tested), low (MSI-L, <30% markers unstable), or stable (MSS, no unstable markers). We used unconditional logistic regression to evaluate the association between each polymorphism and colorectal cancer after adjusting for age and sex. The associations between polymorphisms and tumor clinicopathologic features were evaluated with a Pearson's chi-square or Fisher's exact test. All statistical tests were two-sided.

RESULTS

We observed strong associations between the MLH1 -93G>A polymorphism and MSI-H tumors among case patients from Ontario (P = .001) and Newfoundland (P = .003). When compared with the control populations, homozygosity for the MLH1 -93G>A variant allele was associated with MSI-H tumors among case patients in Ontario (adjusted odds ratio [OR] = 3.23, 95% confidence interval [CI] = 1.65 to 6.30) and in Newfoundland (OR = 8.88, 95% CI = 2.33 to 33.9), as was heterozygosity among case patients in Ontario (OR = 1.84, 95% CI = 1.20 to 2.83) and in Newfoundland (OR = 2.56, 95% CI = 1.14 to 5.75). Genotype frequencies were similar among case patients with MSS and MSI-L tumors and control subjects, and the majority of homozygous variant carriers had MSS tumors. Among case patients from Ontario, an association between the MLH1 -93G>A polymorphism and a strong family history of colorectal cancer (for Amsterdam criteria I and II, P = .004 and P = .02, respectively) was observed.

CONCLUSION

In two patient populations, the MLH1 -93G>A polymorphism was associated with an increased risk of MSI-H colorectal cancer.

Activation of Tumor-Specific Splice Variant Rac1b by Dishevelled Promotes Canonical Wnt Signaling and Decreased Adhesion of Colorectal Cancer Cells

Rac1b is a tumor-specific splice variant of the Rac1 GTPase that displays limited functional similarities to Rac1. We have shown previously a novel cross-talk between Rac1 and beta-catenin, which induces canonical Wnt pathway activation in colorectal cancer cells. This prompted us to investigate if Rac1b, frequently overexpressed in colon tumors, contributes to Wnt pathway dysregulation. We show that Rac1b overexpression stimulates Tcf-mediated gene transcription, whereas depletion of Rac1b results in decreased expression of the Wnt target gene cyclin D1. Reconstitution experiments revealed an important difference between Rac1 and Rac1b such that Rac1b was capable of functionally interacting with Dishevelled-3 (Dvl-3) but not beta-catenin to mediate synergistic induction of Wnt target genes. In agreement, Dvl-3 but not beta-catenin caused increased activation of Rac1b levels, which may explain the functional cooperativity displayed in transcription assays. Furthermore, we show that Rac1b negatively regulates E-cadherin expression and results in decreased adhesion of colorectal cancer cells. RNA interference-mediated suppression of Rac1b resulted in reduced expression of Slug, a specific transcriptional repressor of E-cadherin, and a concomitant increase in E-cadherin transcript levels was observed. Intriguingly, mutation of the polybasic region of Rac1b resulted in complete loss of Rac1b stimulatory effects on transcription and suppressive effects on adhesion, indicating the importance of nuclear and membrane localization of Rac1b. Our results suggest that Rac1b overexpression may facilitate tumor progression by enhancing Dvl-3-mediated Wnt pathway signaling and induction of Wnt target genes specifically involved in decreasing the adhesive properties of colorectal cancer cells.

Ascending the learning curve--MSI testing experience of a six-laboratory consortium

According to recently published guidelines, microsatellite instability (MSI) testing of colorectal cancers may be clinically indicated on a significant proportion of all colorectal tumors. To date, nothing has been published regarding the reproducibility of MSI testing between laboratories. We present MSI quality control activities experience of a six center multinational consortium, as laboratories developed competency with MSI testing and interpretation. The aim of this paper is to share lessons learned and to describe the final concordance rates in scoring MSI markers within this consortium.

Cyclooxygenase-2 knockdown by RNA interference in colon cancer

Overexpression of cyclooxygenase-2 (COX-2) is observed early in colon cancer. Treatments with COX-2-specific NSAIDs have been shown to reduce polyp size and polyp number in FAP patients with a predisposition to colorectal adenoma and cancer. However, the use of COX-2-specific NSAIDs in colon cancer patients has recently revealed increased cardiovascular risks. These harmful side effects may be the result of COX-dependent and/or COX-independent mechanisms. RNA interference (RNAi) is a method of post-transcriptional gene silencing intrinsic to cells. This study employed RNAi to specifically knockdown endogenous COX-2 expression in the HT-29 colon cancer cell line, and to observe the apoptotic response as well as 15-hydroxyprostaglandin dehydrogenase (15-PGDH) expression levels. Following treatment with a COX-2 siRNA, we demonstrated a significant knockdown at the protein level of 57% as compared to a non-silencing siRNA control. Protein results were corroborated by concurrent decrease in COX-2 mRNA levels following the same treatment regimen. Despite previous studies using NSAID treatment to implicate COX-2 involvement in apoptosis, we did not observe any alteration in Bcl-2 expression and Caspase-3 activation following COX-2 knockdown in these cells. 15-PGDH, a physiological antagonist of COX-2 in its catabolism of PGE2, showed a modest but significant induction in response to COX-2 knockdown. The precise role of COX-2 in apoptosis and PGE2 regulation remains unclear; however, having shown that down-regulation of endogenous levels of COX-2 can be achieved in colon cancer by RNAi, this strategy should prove to be a valuable tool in revealing the specific function of COX-2 in tumourigenesis.

MYH mutations are rare in prostate cancer

PURPOSE

Oxidative stress is considered a risk factor for prostate cancer development and is associated with the production of reactive oxygen species (ROS). The base excision repair gene MYH protects against ROS-mediated damage to DNA. Inherited MYH mutations predispose to colorectal adenomas and cancer. A compromised base-excision repair function due to defective MYH may contribute to prostate carcinogenesis. Here, we examine the genetic contribution of MYH to prostate cancer risk.

METHODS

Patients diagnosed with high-grade prostatic intraepithelial neoplasia (HGPIN) alone (n = 45), prostate cancer alone (n = 123) or both (n = 82) were screened for the two most common mutations in the MYH gene using PCR-based RFLP analysis. A single patient with an inherited MYH mutation as well as a subset of 26 patients presenting with a family history of colorectal cancer were screened for additional MYH mutations by direct sequencing of the entire coding region.

RESULTS

Biallelic germline mutations in MYH were not detected among prostate cancer patients. Only a single patient was a heterozygous carrier for the Y165C missense mutation. Allelic deletion or somatic mutation of the remaining MYH allele was not identified in this patient's tumor DNA. Two patients harbored V22M polymorphism and three patients were carriers of Q324H polymorphism.

CONCLUSIONS

MYH mutations are unlikely to contribute to prostate cancer risk.

An association between the 4G polymorphism in the PAI-1 promoter and the development of aggressive fibromatosis (desmoid tumor) in familial adenomatous polyposis patients

Aggressive fibromatosis is a mesenchymal neoplasm associated with mutations resulting in beta-catenin mediated transcriptional activation. Plasminogen activator inhibitor-1 (PAI-1) is expressed at a high level in aggressive fibromatosis, and using transgenic mice, we found that PAI-1 plays an important role in aggressive fibromatosis tumor formation. Familial adenomatous polyposis is associated with Adenomatous Polyposis Coli gene mutations resulting in beta-catenin mediated transcriptional activation, yet only some patients develop aggressive fibromatosis. Since PAI-1 expression is influenced by a promoter 4G/5G polymorphism, we investigated the incidence of this polymorphism in familial adenomatous polyposis patients who did and who did not develop aggressive fibromatosis, as well as sporadic aggressive fibromatosis patients. There was a trend towards association of the 4G allele (associated with high PAI-1 expression) with the development of aggressive fibromatosis in familial adenomatous polyposis patients (50% vs. 19%, P = 0.1). In familial adenomatous polyposis patients who did not develop aggressive fibromatosis, there was a significantly lower proportion of patients with a 4G allele compared to the healthy control (19% vs. 51%, P = 0.0286). The lower incidence of 4G polymorphism in the PAI-1 promoter may be preventive against the development of aggressive fibromatosis. This data provides additional evidence supporting an important role for PAI-1 in the pathogenesis of aggressive fibromatosis.

Determination of active sites for H atom rearrangement in dissociative ionization of ethanol

In an electron impact dissociative ionization experiment on C(2)H(5)OH, the formation of molecular ions requiring rearrangement of H atoms has been studied using a momentum spectrometer. H(3) (+), H(2) (+), HOH(+), and H(2)OH(+) observed in the experiment are molecular ions of this type. By comparing the mass spectrum of C(2)H(5)OH with that of its isotopomer C(2)H(5)OD, we determine the proportions of H-bond rearrangements involving carbon and oxygen sites. We find that the formation of H(3) (+) due to the breaking of the O-H bond and rearrangement of the H atoms on the CH(2) site is about 2.5 times as likely as its formation involving atoms from the CH(3) site alone. No such difference is seen in case of the H(2) (+) ion. The role of the O-H bond in formation of all observed ions has been assessed. Kinetic energy distributions of the molecular ions suggest that two or three electronically excited states contribute to their formation.

Cyclooxygenase-2 knockdown by RNA interference in colon cancer

Overexpression of cyclooxygenase-2 (COX-2) is observed early in colon cancer. Treatments with COX-2-specific NSAIDs have been shown to reduce polyp size and polyp number in FAP patients with a predisposition to colorectal adenoma and cancer. However, the use of COX-2-specific NSAIDs in colon cancer patients has recently revealed increased cardiovascular risks. These harmful side effects may be the result of COX-dependent and/or COX-independent mechanisms. RNA interference (RNAi) is a method of post-transcriptional gene silencing intrinsic to cells. This study employed RNAi to specifically knockdown endogenous COX-2 expression in the HT-29 colon cancer cell line, and to observe the apoptotic response as well as 15-hydroxyprostaglandin dehydrogenase (15-PGDH) expression levels. Following treatment with a COX-2 siRNA, we demonstrated a significant knockdown at the protein level of 57% as compared to a non-silencing siRNA control. Protein results were corroborated by concurrent decrease in COX-2 mRNA levels following the same treatment regimen. Despite previous studies using NSAID treatment to implicate COX-2 involvement in apoptosis, we did not observe any alteration in Bcl-2 expression and Caspase-3 activation following COX-2 knockdown in these cells. 15-PGDH, a physiological antagonist of COX-2 in its catabolism of PGE2, showed a modest but significant induction in response to COX-2 knockdown. The precise role of COX-2 in apoptosis and PGE2 regulation remains unclear; however, having shown that down-regulation of endogenous levels of COX-2 can be achieved in colon cancer by RNAi, this strategy should prove to be a valuable tool in revealing the specific function of COX-2 in tumourigenesis.

Genetic instability in human tumors

Genetic, or genomic, instability refers to a series of observed spontaneous genetic changes occurring at an accelerated rate in cell populations derived from the same ancestral precursor. This is far from a new finding, but is one that has increasingly gained more attention in the last decade due to its plausible role(s) in tumorigenesis. The majority of genetic alterations contributing to the malignant transformation are seen in growth regulatory genes, and in genes involved in cell cycle progression and arrest. Genomic instability may present itself through alterations in the length of short repeat stretches of coding and non-coding DNA, resulting in microsatellite instability. Tumors with such profiles are referred to as exhibiting a mutator phenotype, which is largely a consequence of inactivating mutations in DNA damage repair genes. Genomic instability may also, and most commonly, results from gross chromosomal changes, such as translocations or amplifications, which lead to chromosomal instability. Telomere length and telomerase activity, important in maintaining chromosomal structure and in regulating a normal cell's lifespan, have been shown to have a function in both suppressing and facilitating malignant transformation. In addition to such direct sequence and structural changes, gene silencing through the hypermethylation of promoter regions, or increased gene expression through the hypomethylation of such regions, together, form an alternative, epigenetic mechanism leading to instability. Emerging evidence also suggests that dietary and environmental agents can further modulate the contribution of genetic instability to tumorigenesis. Currently, there is still much debate over the distinct classes of genomic instability and their specific roles in the initiation of tumor formation, as well as in the progressive transition to a cancerous state. This review examines the various molecular mechanisms that result in this genomic instability and the potential contribution of the latter to human carcinogenesis.

Family history and molecular features of children, adolescents, and young adults with colorectal carcinoma

BACKGROUND

Colorectal cancer is extremely rare in childhood. Published case series reporting children and adolescents with colorectal cancer have not focused on the underlying genetic aspects of the tumour or genetic susceptibility of the families.

AIMS

We examined a cohort of patients with early onset colorectal cancer to determine whether a specific genetic predisposition could be elucidated. In particular, we focused on whether DNA mismatch repair gene deficiency which causes hereditary non-polyposis colorectal cancer (HNPCC) could be elucidated.

METHODS

Patients with colorectal cancer </=24 years of age were identified from a database at the Familial Gastrointestinal Cancer Registry at Mount Sinai Hospital, Toronto. Detailed pedigrees were ascertained from the proband or parents. Tumours were tested for microsatellite instability, a hallmark of HNPCC. Germline mismatch repair gene mutations (MSH2 and MLH1) were sought in some cases. Clinical data were obtained by chart audit.

RESULTS

Among 1382 probands in our registry, 16 (1%) colorectal cancer patients were 24 years or younger at the time of diagnosis. Microsatellite instability was identified in tumours from eight (73%) of 11 evaluated patients. Germline mutations in mismatch repair genes were identified in six of 12 patients, including MSH2 (n = 3), MLH1 (n = 2), and PMS2 (n = 1). Ten (63%) of 16 families met the Amsterdam criteria for HNPCC. Among these, six were screened for mismatch repair gene mutations and three were found to carry MSH2 or MLH1 germline mutations. Location of the colorectal cancers included rectum/sigmoid (n = 9), splenic flexure (n = 2), hepatic flexure (n = 3), and caecum (n = 2). Forty four per cent (7/16) of these young cases developed additional malignancies (gastrointestinal (n = 8) and extraintestinal (n = 4)) during follow up (mean 12.8 (SD 12.4) years (range 0.08-30)).

CONCLUSIONS

Patients with early onset colorectal carcinoma often have an inherited predisposition to the disease. Tumours with high frequency microsatellite instability and germline mutations of mismatch repair genes are sufficiently common in this patient population that they should be considered, even though family histories may not satisfy the stringent Amsterdam criteria for HNPCC. Young colorectal cancer patients are at increased risk of developing second gastrointestinal and extraintestinal malignancies.

Lower cancer incidence in Amsterdam-I criteria families without mismatch repair deficiency: familial colorectal cancer type X

CONTEXT

Approximately 60% of families that meet the Amsterdam-I criteria (AC-I) for hereditary nonpolyposis colorectal cancer (HNPCC) have a hereditary abnormality in a DNA mismatch repair (MMR) gene. Cancer incidence in AC-I families with MMR gene mutations is reported to be very high, but cancer incidence for individuals in AC-I families with no evidence of an MMR defect is unknown.

OBJECTIVE

To determine if cancer risks in AC-I families with no apparent deficiency in DNA MMR are different from cancer risks in AC-I families with DNA MMR abnormalities.

DESIGN, SETTING, AND PARTICIPANTS

Identification (1997-2001) of 161 AC-I pedigrees from multiple population- and clinic-based sources in North America and Germany, with families grouped into those with (group A) or without (group B) MMR deficiency by tumor testing. A total of 3422 relatives were included in the analyses.

MAIN OUTCOME MEASURES

Cancer incidence in groups A and B (excluding the 3 affected members used to define each pedigree as AC-I) and computed age- and sex-adjusted standardized incidence ratios (SIRs) using Surveillance, Epidemiology, and End Results data.

RESULTS

Group A families from both population- and clinic-based series showed increased incidence of the HNPCC-related cancers. Group B families showed increased incidence only for colorectal cancer (SIR, 2.3; 95% confidence interval, 1.7-3.0) and to a lesser extent than group A (SIR, 6.1; 95% confidence interval, 5.2-7.2) (P<.001).

CONCLUSIONS

Families who fulfill AC-I criteria but who have no evidence of a DNA MMR defect do not share the same cancer incidence as families with HNPCC-Lynch syndrome (ie, hereditary MMR deficiency). Relatives in such families have a lower incidence of colorectal cancer than those in families with HNPCC-Lynch syndrome, and incidence may not be increased for other cancers. These families should not be described or counseled as having HNPCC-Lynch syndrome. To facilitate distinguishing these entities, the designation of "familial colorectal cancer type X" is suggested to describe this type of familial aggregation of colorectal cancer.

Intraductal papillary mucinous neoplasm of the pancreas in a patient with attenuated familial adenomatous polyposis

A 67 year old man with a clinical diagnosis of attenuated familial adenomatous polyposis (AFAP) and a past history of synchronous colon cancers in the transverse colon was also found to have an intraductal papillary mucinous neoplasm (IPMN) of the pancreas. In addition, several foci of heterotopic gastric oxyntic mucosa were noted in the duodenum, interspersed with flat and polypoid adenomas. The duodenal adenomas showed low grade dysplasia, loss of adenomatous polyposis coli (APC) protein expression, but retention of beta catenin staining, localised to the nucleus and cytoplasm. The IPMN in the pancreas showed an identical immunohistochemical profile to the duodenal adenomas. The heterotopic gastric foci in the duodenum were negative for the APC protein, and beta catenin staining was membranous in location. Although the patient did not show germline truncating APC mutations or mutations in the MYH gene, the past history, clinical features, and immunohistochemical profile of the various lesions suggest strongly that the IPMN is part of the spectrum of lesions encountered in AFAP. Whether the heterotopic oxyntic gastric mucosa in the duodenum is also related is unclear, but it may represent a forme fruste of fundic gland polyps.

Conversion analysis for mutation detection in MLH1 and MSH2 in patients with colorectal cancer

CONTEXT

The accurate identification and interpretation of germline mutations in mismatch repair genes in colorectal cancer cases is critical for clinical management. Current data suggest that mismatch repair mutations are highly heterogeneous and that many mutations are not detected when conventional DNA sequencing alone is used.

OBJECTIVE

To evaluate the potential of conversion analysis compared with DNA sequencing alone to detect heterogeneous germline mutations in MLH1, MSH2, and MSH6 in colorectal cancer patients.

DESIGN, SETTING, AND PARTICIPANTS

Multicenter study with patients who participate in the Colon Cancer Family Registry. Mutation analyses were performed in participant samples determined to have a high probability of carrying mismatch repair germline mutations. Samples from a total of 64 hereditary nonpolyposis colorectal cancer cases, 8 hereditary nonpolyposis colorectal cancer-like cases, and 17 cases diagnosed prior to age 50 years were analyzed from June 2002 to June 2003.

MAIN OUTCOME MEASURES

Classification of family members as carriers or noncarriers of germline mutations in MLH1, MSH2, or MSH6; mutation data from conversion analysis compared with genomic DNA sequencing.

RESULTS

Genomic DNA sequencing identified 28 likely deleterious exon mutations, 4 in-frame deletion mutations, 16 missense changes, and 22 putative splice site mutations. Conversion analysis identified all mutations detected by genomic DNA sequencing--plus an additional exon mutation, 12 large genomic deletions, and 1 exon duplication mutation--yielding an increase of 33% (14/42) in diagnostic yield of deleterious mutations. Conversion analysis also showed that 4 of 16 missense changes resulted in exon skipping in transcripts and that 17 of 22 putative splice site mutations affected splicing or mRNA transcript stability. Conversion analysis provided an increase of 56% (35/63) in the diagnostic yield of genetic testing compared with genomic DNA sequencing alone.

CONCLUSIONS

The data confirm the heterogeneity of mismatch repair mutations and reveal that many mutations in colorectal cancer cases would be missed using conventional genomic DNA sequencing alone. Conversion analysis substantially increases the diagnostic yield of genetic testing for mismatch repair mutations in patients diagnosed as having colorectal cancer.

Apoptotic and growth regulatory genes as mutational targets in mismatch repair deficient endometrioid adenocarcinomas of young patients

Among multiple genetic pathways involved in endometrial cancer (EC), the mutator pathway is characterized by defective mismatch repair (MMR) causing microsatellite instability (MSI+). Inactivation of MMR genes allows elevation of mutation rates in key target genes involved in important cellular pathways, providing a selective growth advantage. Our aim was to investigate apoptotic and growth regulatory target genes in young endometrioid adenocarcinoma patients and their association with stepwise neoplastic progression through distinct stages of hyperplasia and cancer. Screening of 184 ECs revealed 38 microsatellite high (MSI-H), 10 microsatellite low (MSI-L) and 136 microsatellite stable (MSS) tumors. We observed somatic frameshift mutations in the coding region repeats of the target genes in 12/38 MSI-H tumors (T) and in 3/8 of available associated hyperplasias (HY). Mutations were detected in FAS (T=1, HY=1), BAX (T=6, HY=1), CASP5 (T=2) and IGFIIR (T=3, HY=1) genes. None of the MSI-L or MSS tumors showed alterations in these coding repeats. Increased mutation frequency in apoptotic and growth regulatory genes demonstrated a significant relationship with advancing tumor grade (p=0.02) by Fisher's exact test. Furthermore, a significant trend was found by Bartholomew's test (P<0.05) for the apoptotic pathway and close to significant (p approximately 0.06) for the overall mutation status for both pathways combined. Our results suggest that genes implicated in apoptosis may serve as targets in the progression of MSI+ EC in young patients.

Genotype and phenotype of patients with both familial adenomatous polyposis and thyroid carcinoma

The incidence of thyroid carcinoma in familial adenomatous polyposis (FAP) is thought to be 1%-2%, with the majority of cases being female. We have investigated the phenotype and genotype of 16 patients with FAP associated thyroid carcinoma. Among 1194 FAP patients studied in two high risk registries in North America (Familial Gastrointestinal Cancer Registry, Toronto and University California, San Francisco), 16 (1.3%) unrelated patients with FAP associated thyroid cancers were identified. Adenomatous polyposis coli (APC) gene testing was performed in 14 of the 16 cases. The average age of diagnosis for FAP and thyroid carcinoma was 29 years (range 17-52 years) and 33 years (range 17-55 years), respectively. All FAP patients except 1 had more than 100 colonic adenomas. Extracolonic manifestations, beside thyroid cancer, were presented in 81% (n = 13) of the patients, including gastric and duodenal polyps, desmoid tumor, osteoma, epidermoid cyst, sebaceous cyst and lipoma. Colorectal cancer was diagnosed in 38% (n = 6) of the patients. The pathology of the FAP associated thyroid cancer was predominantly papillary carcinoma. Germline mutations were identified in 12 of 14 patients tested. Mutations proximal to the mutation cluster region (1286-1513) were detected in 9 cases. Thyroid cancer in our FAP population was rare, predominantly in females and showed papillary carcinoma histology. Additionally, thyroid cancer in our patients occurred in the setting of classic FAP phenotype. Germline mutations were located predominantly outside the APC mutation cluster region.

Genomic instability and cancer

Tumorigenesis can be viewed as an imbalance between the mechanisms of cell-cycle control and mutation rates within the genes. Genomic instability is broadly classified into microsatellite instability (MIN) associated with mutator phenotype, and chromosome instability (CIN) recognized by gross chromosomal abnormalities. Three intracellular mechanisms are involved in DNA damage repair that leads to mutator phenotype. They include the nucleotide excision repair (NER), base excision repair (BER) and mismatch repair (MMR). The CIN pathway is typically associated with the accumulation of mutations in tumor suppressor genes and oncogenes. Defects in DNA MMR and CIN pathways are responsible for a variety of hereditary cancer predisposition syndromes including hereditary non-polyposis colorectal carcinoma (HNPCC), Bloom syndrome, ataxia-telangiectasia, and Fanconi anaemia. While there are many genetic contributors to CIN and MIN, there are also epigenetic factors that have emerged to be equally damaging to cell-cycle control. Hypermethylation of tumor suppressor and DNA MMR gene promoter regions, is an epigenetic mechanism of gene silencing that contributes to tumorigenesis. Telomere shortening has been shown to increase genetic instability and tumor formation in mice, underscoring the importance of telomere length and telomerase activity in maintaining genomic integrity. Mouse models have provided important insights for discovering critical pathways in the progression to cancer, as well as to elucidate cross talk among different pathways. This review examines various molecular mechanisms of genomic instability and their relevance to cancer.

Projectile-charge sign dependence of four-particle dynamics in helium double ionization

Double ionization of helium by 6 MeV proton impact has been explored in a kinematically complete experiment using a "reaction microscope." For the first time, fully differential cross sections for positively charged projectiles have been obtained and compared with data from 2 keV electron impact. The significant differences observed in the angular distribution of the ejected electrons are attributed to the charge sign of the projectile, resulting in different dynamics of the four-particle Coulomb system, which is not considered in the first Born approximation.