Genetics of colonic cancer

Perturbed myoepithelial cell differentiation in BRCA mutation carriers and in ductal carcinoma in situ

Myoepithelial cells play key roles in normal mammary gland development and in limiting pre-invasive to invasive breast tumor progression, yet their differentiation and perturbation in ductal carcinoma in situ (DCIS) are poorly understood. Here, we investigated myoepithelial cells in normal breast tissues of BRCA1 and BRCA2 germline mutation carriers and in non-carrier controls, and in sporadic DCIS. We found that in the normal breast of non-carriers, myoepithelial cells frequently co-express the p63 and TCF7 transcription factors and that p63 and TCF7 show overlapping chromatin peaks associated with differentiated myoepithelium-specific genes. In contrast, in normal breast tissues of BRCA1 mutation carriers the frequency of p63⁺TCF7⁺ myoepithelial cells is significantly decreased and p63 and TCF7 chromatin peaks do not overlap. These myoepithelial perturbations in normal breast tissues of BRCA1 germline mutation carriers may play a role in their higher risk of breast cancer. The fraction of p63⁺TCF7⁺ myoepithelial cells is also significantly decreased in DCIS, which may be associated with invasive progression.

The Role of Ubiquitination in Regulating Embryonic Stem Cell Maintenance and Cancer Development

Ubiquitination regulates nearly every aspect of cellular events in eukaryotes. It modifies intracellular proteins with 76-amino acid polypeptide ubiquitin (Ub) and destines them for proteolysis or activity alteration. Ubiquitination is generally achieved by a tri-enzyme machinery involving ubiquitin activating enzymes (E1), ubiquitin conjugating enzymes (E2) and ubiquitin ligases (E3). E1 activates Ub and transfers it to the active cysteine site of E2 via a transesterification reaction. E3 coordinates with E2 to mediate isopeptide bond formation between Ub and substrate protein. The E1-E2-E3 cascade can create diverse types of Ub modifications, hence effecting distinct outcomes on the substrate proteins. Dysregulation of ubiquitination results in severe consequences and human diseases. There include cancers, developmental defects and immune disorders. In this review, we provide an overview of the ubiquitination machinery and discuss the recent progresses in the ubiquitination-mediated regulation of embryonic stem cell maintenance and cancer biology.

Demonstration of Herpes Simplex Virus, Cytomegalovirus, and Epstein-Barr Virus in Colorectal Cancer

Background:

The present study sought to investigate molecular evidence for association between the presence of herpes simplex virus (HSV), cytomegalovirus (CMV), and Epstein-Barr virus (EBV) in CRC and colorectal polyp by using the PCR method in Iran.

Methods:

In this analytical case-control study, we selected 15 patients with CRC, 20 patients with colorectal polyp, and 35 patients without malignancy as controls. After DNA extraction, PCR was used to determine HSV, CMV, and EBV genome by specific primers. Statistical analysis was performed using χ² tests.

Results:

Our findings demonstrated that there is no direct molecular evidence to support the association between HSV, CMV, and EBV and human colorectal malignancies.

Conclusion:

The results from this study do not exclude a possible oncogenic role of these viruses in neoplastic development of colon cells.

Resveratrol affects protein kinase C activity and promotes apoptosis in human colon carcinoma cells

BACKGROUND

Resveratrol has been reported to have potential chemopreventive and apoptosis-inducing properties in a variety of tumor cell lines.

OBJECTIVE

In this study, to investigate the effects of resveratrol on protein kinase C (PKC) activity and apoptosis in human colon carcinoma cells, we used HT-29 cells and examined the PKCα and ERK1/2 signaling pathways.

METHODS

To test the effects of resveratrol on the growth of HT- 29 cells, the cells were exposed to varying concentrations and assessed with the the MTT cell-viability assay. Fluorescence-activated cell sorter (FACS) analysis was applied to determine the effects of resveratrol on cell apoptosis. Western blotting was performed to determine the protein levels of PKCα and ERK1/2. In inhibition experiments, HT-29 cells were treated with Go?6976 or PD98059 for 30 min, followed by exposure to 200 μM resveratrol for 72 h.

RESULTS

Resveratrol had a significant inhibitory effect on HT-29 cell growth. FACS revealed that resveratrol induced apoptosis. Western blotting showed that e phosphorylation of PKCα and ERK1/2 was significantly increased in response to resveratrol treatment. Pre-treatment with PKCα and ERK1/2 inhibitors (Go?6976 and PD98059) promoted apoptosis.

CONCLUSION

Resveratrol has significant anti-proliferative effects on the colon cancer cell line HT-29. The PKC- ERK1/2 signaling pathway can partially mediate resveratrol-induced apoptosis of HT-29 cells.

Atypical presentation of colon adenocarcinoma: a case report

Introduction

Adenocarcinoma of the colon is the most common histopathological type of colorectal cancer. In Western Europe and the United States, it is the third most common type and accounts for 98% of cancers of the large intestine. In Uganda, as elsewhere in Africa, the majority of patients are elderly (at least 60 years old). However, more recently, it has been observed that younger patients (less than 40 years of age) are presenting with the disease. There is also an increase in its incidence and most patients present late, possibly because of the lack of a comprehensive national screening and preventive health-care program. We describe the clinicopathological features of colorectal carcinoma in the case of a young man in Kampala, Uganda.

Case presentation

A 27-year-old man from Kampala, Uganda, presented with gross abdominal distension, progressive loss of weight, and fever. He was initially screened for tuberculosis, hepatitis, and lymphoma, and human immunodeficiency virus/acquired immunodeficiency syndrome infection. After a battery of tests, a diagnosis of colorectal carcinoma was finally established with hematoxylin and eosin staining of a cell block made from the sediment of a liter of cytospun ascitic fluid, which showed atypical glands floating in abundant extracellular mucin, suggestive of adenocarcinoma. Ancillary tests with alcian blue/periodic acid Schiff and mucicarmine staining revealed that it was a mucinous adenocarcinoma. Immunohistochemistry showed strong positivity with CDX2, confirming that the origin of the tumor was the colon.

Conclusions

Colorectal carcinoma has been noted to occur with increasing frequency in young adults in Africa. Most patients have mucinous adenocarcinoma, present late, and have rapid disease progression and poor outcome. Therefore, colorectal malignancy should no longer be excluded from consideration only on the basis of a patient's age. A high index of suspicion is important in the diagnosis of colorectal malignancy in young African patients.

Association between methylation in mismatch repair genes, V600E BRAF mutation and microsatellite instability in colorectal cancer patients

Colorectal cancer (CRC) corresponds to the third most prevalent type of cancer. Its origins can either be sporadic or inherited, being Lynch syndrome the most common form of hereditary CRC. The activation of BRAF oncogene, inactivation of mismatch repair genes by methylation of CpG islands, and microsatellite instability (MSI) have been reported to be involved in CRC development. The goal of the study was to characterize CRC tumors using clinical and molecular criteria through association and cluster analysis. Amsterdam II and Bethesda guidelines and molecular variables were analyzed in 77 patients from Brazil. The replication error (RER) status, based in microsatellite instability, showed association with metachronous tumor, MLH1 gene methylation and inverse association with left-sided and synchronous tumors. The PMS2 gene was considered the best predictor for differentiating levels of methylation and the mononucleotide were considered the best markers to evaluate RER status. The cluster 1 was characterized of individuals over 60 years of age, female, right-sided tumor, high microsatellite instability, and metachronous or synchronous tumors. The individuals in cluster 2 were younger than 45 years of age, male and showed left sided or rectum tumors, and microsatellite stability. Even though it was not observed a significant association, a higher number of individuals with family history of cancer and tumors without promoter methylation were found in cluster 2. The V600E mutation did not show association with clinical or molecular characteristics. Evaluation of MSI and methylation of MLH1 and PMS2 genes should be considered in order to assist with clinical diagnosis.

Genomic evolution in Barrett's adenocarcinoma cells: critical roles of elevated hsRAD51, homologous recombination and Alu sequences in the genome

A prominent feature of most cancers including Barrett's adenocarcinoma (BAC) is genetic instability, which is associated with development and progression of disease. In this study, we investigated the role of recombinase (hsRAD51), a key component of homologous recombination (HR)/repair, in evolving genomic changes and growth of BAC cells. We show that the expression of RAD51 is elevated in BAC cell lines and tissue specimens, relative to normal cells. HR activity is also elevated and significantly correlates with RAD51 expression in BAC cells. The suppression of RAD51 expression, by short hairpin RNA (shRNA) specifically targeting this gene, significantly prevented BAC cells from acquiring genomic changes to either copy number or heterozygosity (P<0.02) in several independent experiments employing single-nucleotide polymorphism arrays. The reduction in copy-number changes, following shRNA treatment, was confirmed by Comparative Genome Hybridization analyses of the same DNA samples. Moreover, the chromosomal distributions of mutations correlated strongly with frequencies and locations of Alu interspersed repetitive elements on individual chromosomes. We conclude that the hsRAD51 protein level is systematically elevated in BAC, contributes significantly to genomic evolution during serial propagation of these cells and correlates with disease progression. Alu sequences may serve as substrates for elevated HR during cell proliferation in vitro, as they have been reported to do during the evolution of species, and thus may provide additional targets for prevention or treatment of this disease.

Identification of an MSI-H tumor-specific cytotoxic T cell epitope generated by the (-1) frame of U79260(FTO)

Microsatellite instability (MSI-H) induced by defects of the DNA mismatch repair system results in insertion or deletion of single nucleotides at short repetitive DNA sequences. About 15% of sporadic and approximately 90% of hereditary nonpolyposis colorectal cancers display MSI-H. When affecting coding regions, MSI-H results in frameshift mutations and expression of corresponding frameshift peptides (FSPs). Functional tumor promoting relevance has been demonstrated for a growing number of genes frequently hit by MSI-H. Contrary, immune reactions against FSPs are involved in the immune surveillance of MSI-H cancers. Here, we provide conclusive data that the (−1) frame of U79260(FTO) encodes an HLA-A0201-restricted cytotoxic T cell epitope (FSP11; TLSPGWSAV). T cells specific for FSP11 efficiently recognized HLA-A0201^(pos) tumor cells harboring the mutated reading frame. Considering the exceptionally high mutation rate of U79260(FTO) in MSI-H colorectal carcinoma (81.8%), this recommends that FSP11 be a component of future vaccines.

Cancer stem cells: the other face of Janus

Advances in the field of stem cell biology have provided renewed hopes that stem cells can be used to treat a wide range of genetic diseases and traumatic injuries. However, advances in the field of cancer cell biology have led to formulation of the cancer stem cell hypothesis, which posits that cancers arise from mutant stem cells. Further, this hypothesis proposes that these stem cells account for cancer recurrence, metastasis, and resistance to conventional treatments. Thus, although normal stem cells represent potential effective solutions to numerous clinical problems, when mutated, they may also represent the cause of many human malignancies.

[Peutz-Jeghers' syndrome with malignant development in a hamartomatous polyp: report of one case and review of the literature]

The malignant potential of hamartomatous polyps in Peutz-Jeghers' (PPJ) syndrome has been debated. Although it is a very rare event, these polyps can become malignant, as demonstrated by this report. One case of colonic adenocarcinoma associated with Peutz-Jeghers' syndrome is described in a 62-year-old woman. The patient had colonic carcinoma which developed in a hamartomatous polyp. The malignant development of this colonic hamartomatous polyp arising in Peutz-Jeghers' syndrome was pathologically confirmed at surgery. This case also shows a sequence of hamartoma-dysplasia-carcinoma in a hamartomatous polyp without adenomatous changes. This suggests that hamartomatous polyps in Peutz-Jeghers' syndrome may develop into adenocarcinoma and may be a precursor of gastrointestinal carcinomas. STK 11 is a tumor suppressor gene regulating the development of hamartomas, and this somatic mutation promotes gastrointestinal cancer at later stages in Peutz-Jeghers' syndrome.

Clinicopathological and molecular characteristics of gastric and colorectal carcinomas in the elderly

The occurrence of malignant neoplasms increases with advancing age. Although aging and carcinogenesis are basically different processes, there are phenomena common to each such as accumulation of DNA damage and abnormal proteins. Gastric and colorectal carcinomas are representative tumors in which the prevalence and the number of patients increase significantly with age. Compared with gastric and colorectal cancers occurring in younger patients, those occurring in older patients have clinicopathological differences in tumor location, gender distribution, histological type, histological diversity, multiplicity, incidence of lymph node metastasis, and prognosis. In the elderly there are peculiar types of carcinoma such as medullary-type poorly differentiated colorectal adenocarcinoma and solid-type poorly differentiated gastric adenocarcinoma, both of which occur in older women. Methylation, apoptosis, and telomere dysfunction play important roles in the development of gastric and colorectal cancers in the elderly.

Evidence for an association of human papillomavirus infection and colorectal cancer

AIM

To investigate the presence of human papillomavirus (HPV) in colorectal carcinomas and the correlation of the viral infection with prognostic factors for the disease outcome.

METHODS

Seventy-two patients with primary colorectal adenocarcinoma were studied. From each patient two tissue samples were collected: one sample of the tumor and one sample of normal colorectal tissue from an area located 15 cm away from the tumor. Samples of colorectal mucosa obtained from 30 individuals without malignant disease were also studied as control group. Tissues were initially analyzed through MY/GP nested polymerase chain reaction (PCR) and through GP5+/GP6+ auto-nested PCR. Specific primer sets targeting the E6/E7 region of the HPVs 6, 11, 16, 18, 31, 33, 45 were used for typing. Direct DNA sequencing was conducted to confirm positive PCR results.

RESULTS

HPV DNA was detected in colorectal specimens of 60 patients with cancer (83.3%), but in none of the tissues from the non-malignant control group (p<0.001). Twenty-three cancer patients had HPV DNA detected in both the tumor and the matched normal tissue, 23 had HPV only in the tumor, and 14 had HPV only in the normal colorectal tissue. HPV16 was the viral type most frequently detected, being present in 41 out of 60 positive cases (68.3%). No correlation between the presence of the virus and specific prognostic predictors for the disease outcome was observed.

CONCLUSION

HPV is present in the colon and rectum of most patients with colorectal adenocarcinoma, suggesting that this virus may be related to the pathogenesis of colorectal cancer.

Case control study of the geographic variability of exposure to disinfectant byproducts and risk for rectal cancer

BACKGROUND

Levels of byproducts that result from the disinfection of drinking water vary within a water distribution system. This prompted us to question whether the risk for rectal cancer also varies, depending upon one's long term geographic location within the system. Such a geographic distribution in rectal cancer risk would follow naturally from an association between level of byproduct and rectal cancer risk. We assess the effects of estimated geographic variability in exposure to some of the components of the trihalomethane group of disinfectant byproducts (DBPs) on the odds ratios and probabilities for rectal cancer in white males in a case control study of 128 cases and 253 controls, conducted in Monroe County, Western New York State, U.S.A. The study was designed around health data initially collected at the University at Buffalo (Department of Social and Preventative Medicine) as part of the Upstate New York Diet Study, and trihalomethane (THM) data collected from a separate independent study of THMs conducted by Monroe County Department of Health. Case participants were chosen from hospital pathology records. The controls are disease-free white males between 35-90 years old, living in Monroe County, and chosen from control groups for studies from cancer of five other (unrelated) sites. Using a combination of case control methodology and spatial analysis, the spatial patterns of THMs and individual measures of tap water consumption provide estimates of the effects of ingestion of specific amounts of some DBPs on rectal cancer risk. Trihalomethane (THM) data were used to spatially interpolate levels at the taps of cases and controls, and odds ratios were estimated using logistic regression to assess the effects of estimated THM exposure dose on cancer risk, adjusting for alcohol, dietary beta carotene intake, tap water intake, and total caloric intake.

RESULTS

Trihalomethane levels varied spatially within the county; although risk for rectal cancer did not increase with total level of trihalomethanes, increasing levels of the component bromoform (measured in ug/day) did correspond with an increase in odds ratios (OR = 1.85; 95% CI = 1.25 - 2.74) for rectal cancer. The highest quartiles of estimated consumption of bromoform (1.69-15.43 ug/day) led to increased risk for rectal cancer (OR = 2.32; 95% CI = 1.22-4.39). Two other THMs were marginally associated with an increase in risk - chlorodibromomethane (OR = 1.78, 95% CI = 1.00-3.19) and bromodichloromethane (OR = 1.15; 95% CI = 1.00-1.32).

CONCLUSION

Levels of THMs in the water distribution system exhibited spatial variation that was partially due to variation in water age. We also observed a geographic pattern of increased risk of rectal cancer in areas with the highest levels of bromoform in the county.

[Role of the genetic polymorphism of p53 (codon 72) gene in colorectal cancer]

BACKGROUND

Polymorphisms are genetic variations that can occur in sequences of codons, leading to defective proteins. p53 is the most commonly gene affected in human cancer. The polymorphism of this gene occurs by a substitution of a base in codon 72 and may increase the risk of cancer.

AIM

To investigate the possible association between p53 arginine/72 proline polymorphism and susceptibility to colorectal cancer.

PATIENTS AND METHODS

This polymorphism was studied by polymerization chain reaction using specific primers in 100 patients with colorectal cancer paired by sex and age to 100 patients without cancer. Alcohol and tobacco used by all the patients and clinical aspects as stage, grade of differentiation and recurrence in the case group was compared with the genotype analyzed.

RESULTS

The frequency of homozygosis for arginine was 56% in the cancer group and 58% in the control group. No significant difference was observed among both groups. This genotype was more frequent in colorectal cancer patients stage IV than in stage I (80% versus 14%). There was no significant difference between genotypes and alcohol, tobacco, grade of differentiation or recurrence.

CONCLUSION

Homozygosity for arginine was the most prevalent genotype in both groups. The frequency of codon 72 proline/arginine p53 gene polymorphism was not correlated with a higher risk of colorectal cancer. Arginine/arginine genotype was more prevalent in advanced cancer patients (stage IV).

Prognostic value of p16INK4a and p14ARF gene hypermethylation in human colon cancer

The INK4a/ARF locus (9p21) encodes two unique and unrelated cell cycle regulators, p16INK4a and p14ARF. This study was performed to evaluate the methylation status of p16INK4a and p14ARF genes, as well as its association with p16 and p53 expression, microsatellite instability (MI) status, and various clinicopathologic parameters in sporadic colorectal cancer. Sixty-five cases of primary colorectal adenocarcinoma with a series of clinicopathological parameters were obtained. We performed methylation-specific PCR of p16INK4a and p14ARF genes in colorectal cancer paraffin blocks with its paired normal samples, as well as immunohistochemical stainings for p16 and p53, and MI analysis. Aberrant methylations of p16INK4a and p14ARF gene were present in 21 (32.3%) and 33 (50.8%) out of 65 cases, respectively. p16INK4a aberrant methylation was correlated with p16 negativity (P=0.021) and p53 overexpression (P=0.007). p16INK4a aberrant methylation was more frequently present in poorly differentiated adenocarcinomas (P=0.002). Aberrant methylation of p14ARF gene occurred more frequently in patients under 50 years of age and in left-sided colon cancers, and was not statistically significant. Compared with the group with simultaneous absence of methylation in both promoters, the group showing concomitant alterations in both p16INK4a and p14ARF genes (n=10) more frequently presented lymph node metastasis (P=0.020) and higher tumor grade (P=0.014). There was no correlation between p16INK4a and p14ARF gene hypermethylation or MI status. This study suggests that simultaneous hypermethylation of both p16INK4a and p14ARF genes is greater prognostic value in sporadic human colorectal cancer.

Molecular pathogenesis of colorectal cancer: implications for molecular diagnosis

Colorectal cancer is the third leading cause of cancer-related death in both men and woman in industrialized countries. Major advances have been made in our understanding of molecular events leading to formation of adenomatous polyps and cancer. Most colorectal cancers are sporadic, but a significant proportion (5-6%) has a clear genetic background. It is now widely accepted that colorectal carcinogenesis is a multistep process involving the inactivation of a variety of tumor-suppressor and DNA-repair genes and simultaneous activation of certain oncogenes. In addition, epigenetic alterations through aberrant promoter methylation and histone modification have been found to play a major role in the evolution and progression of a large proportion of sporadic colon cancers. Consequently, it is now apparent that individual colorectal cancers may evolve through diverse molecular pathways. In this article, the authors have summarized the current knowledge of molecular pathogenesis in common hereditary syndromes and sporadic forms of colorectal cancer. Novel molecular diagnostic tools for the early diagnosis and prevention of colorectal cancer that have emerged from these insights are discussed.

Hereditary non-polipomatous colorectal cancer: hereditary predisposition, diagnosis and prevention

BACKGROUND: Colorectal cancer is the third in frequency and the second in mortality in developed countries. In Brazil, it is among the six more common malignant neoplasias. About 20% of colorectal tumors have some hereditary component. AIM: This study presents a review of genetic and clinic aspects, as well as diagnosis and prevention of the hereditary non-polipomatous colorectal cancer, that is the more frequent form of hereditary colorectal cancer. This approach is important because, currently there are possibilities of management, prevention and surveillance specific to individuals at-risk for hereditary non-polipomatous colorectal cancer that can lead to a great improvement in patients' survival and their at-risk relatives.

Germline epimutation of MLH1 in individuals with multiple cancers

Epigenetic silencing can mimic genetic mutation by abolishing expression of a gene. We hypothesized that an epimutation could occur in any gene as a germline event that predisposes to disease and looked for examples in tumor suppressor genes in individuals with cancer. Here we report two individuals with soma-wide, allele-specific and mosaic hypermethylation of the DNA mismatch repair gene MLH1. Both individuals lack evidence of genetic mutation in any mismatch repair gene but have had multiple primary tumors that show mismatch repair deficiency, and both meet clinical criteria for hereditary nonpolyposis colorectal cancer. The epimutation was also present in spermatozoa of one of the individuals, indicating a germline defect and the potential for transmission to offspring. Germline epimutation provides a mechanism for phenocopying of genetic disease. The mosaicism and nonmendelian inheritance that are characteristic of epigenetic states could produce patterns of disease risk that resemble those of polygenic or complex traits.

Hereditary nonpolyposis colorectal cancer: preventive management

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common form of hereditary colorectal cancer. Inherited mutations in the mismatch repair genes associated with this syndrome have an approximate 80% lifetime risk of colorectal cancer. Since there are no premonitory signs of susceptibility to HNPCC, family history is the initial method for identifying those at increased risk. At risk individuals should undergo genetic counseling and testing. Although an algorithmic indication for genetic testing in at risk HNPCC patients is yet to be determined, many advocate initial screening for microsatellite instability (MSI) of the cancer specimen in individuals suspected of carrying HNPCC mutations. Those who test positive for MSI can then undergo further testing for mutations in the associated germline mismatch repair genes. Techniques for detecting these mutations currently include in vitro synthesized-protein assay, single-strand conformational polymorphism, and DNA sequencing. Given the aggressive nature of HNPCC adenomas, individuals who test positive for HNPCC mutations are recommended to undergo yearly colonoscopic surveillance starting at the age of 25. A reasonable alternative to lifetime colonoscopic surveillance for the prevention of colorectal cancer in these individuals is prophylactic colectomy. The prevention of colorectal cancer through pharmacological means is under investigation as another option in the management of HNPCC patients. Specifically, chemoprevention trials are currently ongoing to evaluate the efficacy of COX-2 inhibitors in the prevention of colorectal cancer in HNPCC and familial adenomatous polyposis patients.

Role of hMLH1 promoter hypermethylation in drug resistance to 5-fluorouracil in colorectal cancer cell lines

Loss of DNA mismatch repair (MMR) occurs in 10-15% of sporadic colorectal cancer, is usually caused by hMLH1 hypermethylation, and has been shown to confer resistance to various chemotherapeutic reagents, including 5-fluorouracil (5-FU). We tested the hypothesis that demethylation of the hMLH1 promoter in hypermethylated colorectal cancer cells would restore MMR proficiency and drug sensitivity to 5-FU. We used the MMR-deficient cell lines SW48, HCT116, HCT116+chr2 and the -proficient cell line HCT116+chr3. After treatment with the demethylating agent 5-Aza-2'-deoxycytidine (5 aza-dC), hMLH1 mRNA and protein expression were determined by RT-PCR and immunoblots. The methylation status for hMLH1 was investigated by methylation-specific PCR. Cells were subsequently treated with 5-FU and the growth characteristics ascertained by clonogenic assays. hMLH1 hypermethylation was reverted in SW48 cells 24 hr after treatment with 5 aza-dC and was accompanied by hMLH1 mRNA and protein reexpression. While 5 aza-dC alone did not affect the growth of SW48 cells, all other cell lines responded with a pronounced growth inhibition. 5-FU treatment strongly reduced the colony formation of HCT116+chr3 cells. These effects were significantly less in the MMR-deficient cells. Combined treatment of SW48 cells resulted in a similar growth pattern as seen in 5-FU only treated HCT116+chr3 cells. We demonstrate that in vitro resistance to 5-FU can be overcome by reexpression of hMLH1 protein through 5 aza-dC-induced demethylation in hypermethylated cell lines. Induction of the expression of methylated tumor suppressor or MMR genes could have a significant impact on the development of future chemotherapy strategies.

Poor prognosis of colorectal cancer in patients over 80 years old is associated with down-regulation of tumor suppressor genes

GOALS, BACKGROUND: The elderly population has been increasing during the last half a century and it would be important to know how aging influences the occurrence and biologic behavior of cancers.

STUDY

We investigated clinicopathologic characteristics of colorectal cancer in 1354 patients who underwent colorectal cancer resection and compared the results between extremely elderly patients (over 80 years old) and middle-aged/elderly patients (40 to less than 80 years old). Furthermore, we also examined expression of tumor suppressor genes and Cox-2 using frozen samples of colorectal cancer obtained from 62 patients ranging in age from 45 to 87 years.

RESULTS

The results obtained in the extremely aged patients were: (1) higher ratio of women, (2) higher incidence at the proximal site, (3) higher incidence of cases with deeper invasion, (4) higher incidence of cases with lymph node metastasis (5) poorer survival rate as compared with middle-aged/elderly patients, and (6) lower mRNA expression levels of p27 and p53.

CONCLUSIONS

These findings taken together suggest that poor prognosis of colorectal cancer in patients over 80 years is associated with down-regulation of mRNA expression of some tumor suppressor genes.

Long-term trends in cancer mortality in the United States, 1930-1998

BACKGROUND

Progress against cancer can be examined by analyzing long-term trends in cancer incidence and mortality. The recent directive from the U.S. Department of Health and Human Services to adopt the 2000 U.S. standard population for the age adjustment of death rates prompted the American Cancer Society to update historical cancer mortality statistics using the new standard.

METHODS

Mortality data were abstracted by race, gender, year, and age at death for 1930 through 1959 from annual volumes of Vital Statistics of the United States. For 1960 through 1998, these data were obtained from data tapes provided by the National Center for Health Statistics. Two U.S. standard million populations (1970 and 2000) were used to calculate age-adjusted rates. Average annual percent change was estimated for each decade by site, gender, and age, and the statistical significance of the change was assessed at p < 0.05.

RESULTS

After long-term increases or mostly level trends that date from the 1930s for some sites, death rates for cancers of the lung (in males), prostate, female breast, colon-rectum, pancreas, leukemia, and ovary were decreasing in the 1990s. Liver cancer death rates were increasing in the 1990s. Throughout the study period, death rates for female lung cancer increased, while death rates for stomach and uterine cancers declined.

CONCLUSIONS

The trends of decreasing cancer death rates for the leading cancer sites in the 1990s are encouraging. However, surveillance researchers must continue to monitor these declines to assess whether the progress seen in this decade persists. Efforts also must be made to study the sites with increasing trends and identify potential underlying causes.

Hereditary renal cancers

Hereditary renal cancer syndromes can lead to multiple bilateral kidney tumors that occur at a younger age than do nonhereditary renal cancers. Imaging plays an important role in the diagnosis and management of these syndromes. During the past decade, several new hereditary renal syndromes have been discovered but are not yet widely known. Whereas previously, the list of hereditary renal cancers in adults included von Hippel-Lindau disease and a rare form of chromosomal translocation, the list now includes the following syndromes: tuberous sclerosis, hereditary papillary renal cancer, Birt-Hogg-Dubé syndrome, hereditary leiomyoma renal cell carcinoma, familial renal oncocytoma, hereditary nonpolyposis colon cancer, and medullary carcinoma of the kidney. In addition, a number of newly described but poorly understood syndromes are under investigation. Even at this early stage, it is clear that elucidation of the underlying genetic mutations that cause hereditary renal cancer syndromes will have profound implications for understanding the origins of nonhereditary renal tumors. These studies will likely culminate in a better understanding of the causes of renal cancer, its prevention, and, ultimately, its cure.

Effect of sulindac treatment for attenuated familial adenomatous polyposis with a new germline APC mutation at codon 161: report of a case

INTRODUCTION

Patients with familial adenomatous polyposis develop colorectal cancers if left untreated. As indicated in patients with familial adenomatous polyposis, prophylactic colectomy has been recommended even in a milder colonic phenotype referred to as attenuated familial adenomatous polyposis. However, therapeutic strategies in attenuated familial adenomatous polyposis are still controversial.

METHODS

We report a patient with attenuated familial adenomatous polyposis who has been treated with sulindac for five years. During the period of observation, she has been carefully followed up by chromoscopic and radiographic surveillance. Immunohistochemical study for cyclooxygenase-2 and genetic analysis in the adenomatous polyposis coli gene was also performed.

RESULTS

Continuous administration of sulindac resulted in obvious regression of both colorectal adenomatous polyps and gastric fundic gland polyps, and no cancers developed during the observation period. Immunohistochemical study showed the decrease of cyclooxygenase-2-positive epithelial cells in colorectal polyps by the treatment. The genetic analysis revealed a C to A substitution at nucleotide 481 of her germline adenomatous polyposis coli gene, which resulted in a nonsense mutation at codon 161.

CONCLUSIONS

Our case suggests that treatment with sulindac accompanied by intensive colonoscopic surveillance may be a choice of management for attenuated familial adenomatous polyposis.

Primary prevention: phytoprevention and chemoprevention of colorectal cancer

Considering the various stages of carcinogenesis and the numerous tumor types and available chemoprevention agents, knowledge of the etiology and the type of cancer to be treated, or possibly prevented, and understanding of the mechanisms by which agents exert their chemoprevention benefits may provide for improved strategy in designing therapeutic regimens. Because cancer usually develops over a 10- to 20-year period, it may be necessary for some agents to be provided before or early in the initiation steps of carcinogenesis to have beneficial effects. On the other hand, some agents may be more suitable for CRC prevention if provided at a later stage of carcinogenesis. Gene array, genomics, and proteomics are useful tools in advancing our understanding of the molecular events involved in carcinogenesis and in identifying markers of risk and surrogate end-points for colorectal cancer progression. These techniques may also serve for screening, identifying, and providing treatment targets for high-risk patients populations. Treatment could be developed depending on a patient's individual needs and genomic tumor profile. Clinical markers and surrogate end-points should be considered, together with molecular measurements, to more accurately assess risk. NSAIDs and COXIBs are clinically recognized as chemoprevention agents, and clinical trials evaluating their efficacy are ongoing. Treatment protocols, including dose and timing, remain to be determined, however. DFMO may best be used in combination with other chemoprevention agents. Dietary fiber and calcium supplements, as part of an overall low-fat diet, may decrease CRC risk. Long-term compliance with this regimen may be necessary to effect a beneficial outcome. Folate holds promise but needs further investigation, especially because its beneficial effects may depend on cancer type. Phytochemicals have been identified as strong candidates for use as agents to prevent colorectal cancer in cell culture and in rodent models of carcinogenesis. Their potential as chemoprevention agents must be demonstrated in clinical trials. In vitro and animal studies indicated that combination therapy may be a promising strategy over the monotherapy approach; clinical trials addressing the safety and efficacy of some combinations (DFMO/sulindac, fiber/calcium) are underway. The gastrointestinal tract and other organs are constantly exposed to a mixture of potentially toxic compounds and molecules considered favorable to health. Homeostasis between stress-mediated by toxic compounds and defensive mechanisms, is key for the maintenance of health and the prevention of disease. Whereas aggressive pharmacologic treatment may be necessary for patients at high risk for cancer, dietary supplements may be useful for populations at normal risk. The message for cancer prevention in the general population may well remain: keep a balanced healthy diet, eating a variety from all food groups, as part of a healthy lifestyle that includes moderate exercise.

Challenge in the differentiation between attenuated familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer: case report with review of the literature

The clinical differentiation between hereditary nonpolyposis colorectal cancer (HNPCC) and attenuated familial adenomatous polyposis (AFAP) is very difficult. The 62-yr-old proband presented with duodenal adenocarcinoma. His history of subtotal colectomy for colon cancer, the rarity of duodenal adenocarcinoma in the general population, and his family history of colon cancer made us suspect that he might have FAP. We investigated this family by obtaining medical records and performing gene analysis. The proband had only 10 adenomatous colon polyps when he underwent subtotal colectomy for the cancer, so classic FAP was excluded. His family history included rectal cancer in his brother at 69 yr of age, colon cancer in his mother at 75 yr, and colon cancer in one maternal cousin at 42 yr. Three months after we started to study this family, the proband's 32-yr-old son presented with rectal cancer. His family fulfilled the Amsterdam criteria for HNPCC, but AFAP could not be excluded. Upon gene testing, the proband was negative for APC gene germline mutation, which made AFAP highly unlikely. Moreover, high microsatellite instability (MSI) was detected in his adenomas and cancer tissues. The fulfillment of Amsterdam criteria, the exclusion of FAP and AFAP, and the high MSI established the diagnosis of HNPCC in this family. We also summarize the differences between FAP, AFAP, and HNPCC; extend the graphic description of the MSI mechanism; and propose a diagnostic strategy for HNPCC.

Application of population screening principles to genetic screening for adult-onset conditions

Recent advances in molecular genetics have highlighted the potential use of genetic testing to screen for adult-onset chronic diseases. Several issues must be addressed, however, before such tests can be recommended for population-based prevention programs. These issues include the adequacy of the scientific evidence, the balance of risks and benefits, the need for counseling and informed consent, and the costs and resources required. Ongoing assessment of the screening program and quality assurance of laboratory testing are also needed. This paper considers the application of general principles for mass screening to genetic testing for susceptibility to adult-onset chronic diseases. Evaluation of proposals for genetic screening in context of these principles reveals that needed evidence is often absent, particularly with respect to the predictive value of tests, efficacy of interventions, and social consequences of testing. The principles of population screening are developed into a framework for public health policy on genetic screening that has three stages: assessment of the screening test and interventions for those who test positive, including assessment of risks and costs, policy development, and program evaluation. Essential elements are identified, including evaluation of evidence and processes for consensus development and program evaluation. The proposed framework for public health policymaking outlined in this commentary, when combined with future efforts that involve an authoritative consensus process, may be useful for the evaluation and planning of genetic screening programs aimed at reducing morbidity and mortality from adult-onset chronic diseases.

Awareness of genetic testing for colorectal cancer predisposition among specialists in gastroenterology

OBJECTIVES

Adult gastroenterologists practicing in New York State were surveyed to determine their practice with regard to identifying family histories consistent with inherited forms of colorectal cancer, and to assess their awareness of cancer genetic counseling and molecular genetic testing for familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC).

METHODS

A closed-ended questionnaire was mailed to 815 gastroenterologists identified through the membership Directory of the American Gastroenterological Association (1998). Two mailings resulted in a response rate of 35%.

RESULTS

In all, 99% of the gastroenterologists obtained a family history from their patients, and 95% were aware of cancer genetic counseling. However, only 51% would routinely refer patients for genetic counseling before providing cancer predisposition testing. In addition, only 52% were aware of the availability of genetic tests for FAP and 34% for HNPCC. Presented with a family history consistent with HNPCC, 79% could identify the syndrome, 26% recommended genetic counseling for the consultand, and 16% advised appropriate screening, according to current recommendations.

CONCLUSIONS

The majority of gastroenterologists do obtain a family history on their patients. However, there is a need for physician education regarding the recognition of pedigrees consistent with inherited colorectal cancer, the genetic counseling process, and the availability of mutation testing for FAP and HNPCC.

Differential expression of a novel colorectal cancer differentiation-related gene in colorectal cancer

AIM: To investigate SBA2 expression in CRC cell lines and surgical specimens of CRC and autologous healthy mucosa.

METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) was used for relative quantification of SBA2 mRNA levels in 4 human CRC cell lines with different grades of differentiation and 30 clinical samples. Normalization of the results was achieved by simultaneous amplification of β-actin as an internal control.

RESULTS: In the exponential range of amplification, fairly good linearity demonstrated identical amplification efficiency for SBA2 and β-actin (82%). Markedly lower levels of SBA2 mRNA were detectable in tumors, as compared with the coupled normal counterparts (P < 0.01). SBA2 expression was significantly (0.01 < P < 0.05) correlated with the grade of differentiation in CRC, with relatively higher levels in well-differentiated samples and lower in poorly-differentiated cases. Of the 9 cases with lymph nodes affected, 78% (7/9) had reduced SBA2 mRNA expression in contrast to 24% (5/21) in non-metastasis samples (0.01 < P < 0.05).

CONCLUSION: SBA2 gene might be a promising novel biomarker of cell differentiation in colorectal cancer and its biological features need further studies.

Mutations in apoptosis genes: a pathogenetic factor for human disease

Cell death by apoptosis is exerted by the coordinated action of many different gene products. Mutations in some of them, acting at different levels in the apoptosis process, have been identified as cause or contributing factor for human diseases. Defects in the transmembrane tumor necrosis factor receptor 1 (TNF-R1) lead to the development of familial periodic fever syndromes. Mutations in the homologous receptor Fas (also named CD95; Apo-1) are observed in malignant lymphomas, solid tumors and the autoimmune lymphoproliferative syndrome type I (ALPS I). A mutation in the ligand for Fas (Fas ligand; CD95 ligand, Apo-1 ligand), which induces apoptosis upon binding to Fas, was described in a patient with systemic lupus erythematodes and lymphadenopathy. Perforin, an other cytotoxic protein employed by T- and NK-cells for target cell killing, is mutated in chromosome 10 linked cases of familial hemophagocytic lymphohistiocytosis. Caspase 10, a representative of the caspase family of proteases, which plays a central role in the execution of apoptosis, is defect in autoimmune lymphoproliferative syndrome type II (ALPS II). The intracellular pro-apoptotic molecule bcl-10 is frequently mutated in mucosa-associated lymphoid tissue (MALT) lymphomas and various non-hematologic malignancies. The p53, an executioner of DNA damage triggered apoptosis, and Bax, a pro-apoptotic molecule with the ability to perturb mitochondrial membrane integrity, are frequently mutated in malignant neoplasms. Anti-apoptotic proteins like bcl-2, cellular-inhibitor of apoptosis protein 2 (c-IAP2) and neuronal apoptosis inhibitory protein 1 (NAIP1) are often altered in follicular lymphomas, MALT lymphomas and spinal muscular atrophy (SMA), respectively. This article reviews the current knowledge on mutations of apoptosis genes involved in the pathogenesis of human diseases and summarises the gradual transformation of discoveries in apoptosis research into benefits for the clinical management of diseases.

A multi-stage model of adenoma development

The overwhelming proportion of colorectal carcinomas are believed to originate as adenomatous polyps (adenomas), and the identification and removal of adenomas is an important component of colorectal cancer prevention efforts. Mathematical modeling of adenomas can increase our understanding of the natural history and biology of adenomas and colorectal cancer and can help in the effort to devise optimal prevention and screening strategies. Here we adapt the multi-stage model of carcinogenesis to the problem of the development and growth of adenomas. We show that, using plausible values for the biological parameters, the model can fit various aspects of adenoma data including adenoma prevalence by age, the size distribution of adenomas, clustering of adenomas within individuals and the correlation between distal and proximal adenomas. Explaining the clustering of adenomas within individuals, as well as other findings, requires heterogeneity in risk in the population; we show how such heterogeneity can be related to the distribution of biological parameters in the population. The model can also be adapted to account for adenoma development in two major syndromes related to colorectal cancer, familial adenomatous polyposis and hereditary non-polyposis colorectal cancer.

Pathologic characteristics of colorectal cancer in the elderly: a retrospective study of 947 surgical cases

To determine the pathologic characteristics of colorectal cancer in the very old, a retrospective study of 947 consecutive Japanese patients aged > or =65 with 1,039 lesions were examined. Pathologic findings in the very old group (>85 years, n = 140) were compared with those in the younger groups; young-old group (65-74 years, n = 352) and middle-old group (75-84 years, n = 455). Although male:female ratio significantly decreased with advancing age, reaching 1:1.8 in the very old group, the relative odds of colorectal cancer in men were higher than that in women in all age groups. In the very old group, cancer of the proximal colon (proximal to the splenic flexure) accounted for 52% in women and 37% in men, being significantly higher than those in the younger groups. Proximal colonic cancers increased with advancing age in both genders. Higher proportions of poorly differentiated adenocarcinoma, mucinous carcinoma, cancer >5 cm in size, and protruding type cancer were present in the very old group, although these kinds of tumors typically occur in the proximal colon. The incidence of multiple cancers in the large intestine was not different among any age group (average, 8.6%). These results indicated that, even in the very old, colorectal cancers showed marked proximal excess, being explained by effect of both age and gender, and that the proximal shift may influence the proportion of histologic type and size of the tumor. These findings have important implications for screening and diagnosis of colorectal cancer in the elderly.

The annual report to the nation on the status of cancer, 1973-1997, with a special section on colorectal cancer

BACKGROUND

This annual report to the nation addresses progress in cancer prevention and control in the U.S. with a special section on colorectal cancer. This report is the joint effort of the American Cancer Society, the National Cancer Institute (NCI), the North American Association of Central Cancer Registries (NAACCR), and the Centers for Disease Control and Prevention (CDC), including the National Center for Health Statistics (NCHS).

METHODS

Age-adjusted rates were based on cancer incidence data from the NCI and NAACCR and underlying cause of death as compiled by NCHS. Joinpoint analysis was based on NCI Surveillance, Epidemiology, and End Results (SEER) program incidence rates and NCHS death rates for 1973-1997. The prevalence of screening examinations for colorectal cancer was obtained from the CDC's Behavioral Risk Factor Surveillance System and the NCHS's National Health Interview Survey.

RESULTS

Between 1990-1997, overall cancer incidence and death rates declined. Joinpoint analyses of cancer incidence and death rates confirmed the declines described in earlier reports. The incidence trends for colorectal cancer have shown recent steep declines for whites in contrast to a leveling off of the rates for blacks. State-to-state variations occurred in colorectal cancer screening prevalence as well as incidence and death rates.

CONCLUSIONS

The continuing declines in overall cancer incidence and death rates are encouraging. However, a few of the top ten incidence or mortality cancer sites continued to increase or remained level. For many cancer sites, whites had lower incidence and mortality rates than blacks but higher rates than Hispanics, Asian and Pacific Islanders, and American Indians/Alaska Natives. The variations in colorectal cancer incidence and death rates by race/ethnicity, gender, age, and geographic area may be related to differences in risk factors, demographic characteristics, screening, and medical practice. New efforts currently are underway to increase awareness of screening benefits and treatment for colorectal cancer.

The annual report to the nation on the status of cancer, 1973-1997, with a special section on colorectal cancer

BACKGROUND

This annual report to the nation addresses progress in cancer prevention and control in the U.S. with a special section on colorectal cancer. This report is the joint effort of the American Cancer Society, the National Cancer Institute (NCI), the North American Association of Central Cancer Registries (NAACCR), and the Centers for Disease Control and Prevention (CDC), including the National Center for Health Statistics (NCHS).

METHODS

Age-adjusted rates were based on cancer incidence data from the NCI and NAACCR and underlying cause of death as compiled by NCHS. Joinpoint analysis was based on NCI Surveillance, Epidemiology, and End Results (SEER) program incidence rates and NCHS death rates for 1973-1997. The prevalence of screening examinations for colorectal cancer was obtained from the CDC's Behavioral Risk Factor Surveillance System and the NCHS's National Health Interview Survey.

RESULTS

Between 1990-1997, overall cancer incidence and death rates declined. Joinpoint analyses of cancer incidence and death rates confirmed the declines described in earlier reports. The incidence trends for colorectal cancer have shown recent steep declines for whites in contrast to a leveling off of the rates for blacks. State-to-state variations occurred in colorectal cancer screening prevalence as well as incidence and death rates.

CONCLUSIONS

The continuing declines in overall cancer incidence and death rates are encouraging. However, a few of the top ten incidence or mortality cancer sites continued to increase or remained level. For many cancer sites, whites had lower incidence and mortality rates than blacks but higher rates than Hispanics, Asian and Pacific Islanders, and American Indians/Alaska Natives. The variations in colorectal cancer incidence and death rates by race/ethnicity, gender, age, and geographic area may be related to differences in risk factors, demographic characteristics, screening, and medical practice. New efforts currently are underway to increase awareness of screening benefits and treatment for colorectal cancer.

Does hereditary nonpolyposis colorectal cancer explain the observed excess risk of colorectal cancer associated with family history?

Several studies have found an increased risk of colorectal cancer associated with a family history of colorectal cancer. Some studies, although not all, have also suggested that family history of colorectal cancer may be a risk factor for adenomatous polyps. Hereditary nonpolyposis colorectal cancer is a known genetic syndrome predisposing to colorectal cancer. The hypothesis of this paper is that the preponderance of the genetic or familial risk for colorectal cancer in the United States is mediated by hereditary nonpolyposis colorectal cancer. To test this hypothesis, I have incorporated what is known about hereditary nonpolyposis colorectal cancer into a genetic model that generates probabilities of family clustering of colorectal cancer. Using this model, which assumes that all familial risk for colorectal cancer is due to hereditary nonpolyposis colorectal cancer, the expected relative risks for colorectal cancer (and adenomas) associated with given types of family histories were calculated. The relative risks predicted by the model fairly closely matched the results found in the literature, especially those reported from a large cohort study. As observed in several studies, the model predicts that relative risks decrease sharply with age. In contrast to the elevated risk for colorectal cancer, the model predicts no elevated risk for adenomas associated with family history of colorectal cancer.

Transcription of the inositol polyphosphate 1-phosphatase gene (INPP1) is upregulated in human colorectal cancer

We have used suppression subtractive hybridization to demonstrate significant overexpression of the inositol polyphosphate 1-phosphatase gene (INPP1) in colorectal cancer compared with matched normal colon epithelium. Its gene product catalyses the hydrolysis of inositol 1,3,4-trisphosphate and inositol 1, 4-bisphosphate, a key molecule in the phosphoinositide metabolic and signaling pathways. Following confirmation of the differential expression by reverse Northern dot blot analysis, fully quantitative Taqman reverse transcriptase-polymerase chain reaction assays showed that its transcription was upregulated in 42/49 colorectal tumors. There was no significant difference in four tumors and reduced transcription was observed in three. This is the first study to report the upregulation of the INPP1 gene in a human cancer and should facilitate further studies looking at the role of phosphatidylinositol signaling reactions in human colorectal cancer.

Psychological and behavioral factors associated with colorectal cancer screening among Ashkenazim

BACKGROUND

Psychological and behavioral factors related to annual colorectal cancer (CRC) screening were examined in a sample of Ashkenazi Jewish individuals. Identification of factors related to regular CRC screening in this population is important because of the possibility of a heightened incidence of CRC.

METHODS

Eligible participants were 171 Ashkenazi Jewish adults 40 years or older attending an educational program about breast cancer genetics. Compliance with recommended guidelines for digital rectal examination and fecal occult blood test in the past year were dependent measures. Demographic variables, family history of CRC, perceived risk, physician recommendation, and worry about cancer were independent measures.

RESULTS

Digital rectal examinations and fecal occult blood tests had been obtained in the past year by 46 and 31% of the participants, respectively. A logistic regression showed that physician recommendation was related significantly to obtaining digital rectal examinations. Physician recommendation and education were related significantly to obtaining fecal occult blood tests. Although participants with family histories of CRC perceived themselves as being at increased risk of developing CRC, and were more worried about developing colon cancer, they were no more likely to adhere to CRC screening guidelines than those without such histories.

CONCLUSIONS

Overall, compliance with recommended CRC screening was low even among high-risk individuals. Physicians play a key role in motivating people to comply with CRC screening. Physicians need to en courage all asymptomatic patients 50 years and older to be screened for CRC.

Recombination and its roles in DNA repair, cellular immortalization and cancer

Genetic recombination is the creation of new gene combinations in a cell or gamete, which differ from those of progenitor cells or parental gametes. In eukaryotes, recombination may occur at mitosis or meiosis. Mitotic recombination plays an indispensable role in DNA repair, which presumably directed its early evolution; the multiplicity of recombination genes and pathways may be best understood in this context, although they have acquired important additional functions in generating diversity, both somatically (increasing the immune repertoire) and in germ line (facilitating evolution). Chromosomal homologous recombination and HsRad51 recombinase expression are increased in both immortal and preimmortal transformed cells, and may favor the occurrence of multiple oncogenic mutations. Tumorigenesis in vivo is frequently associated with karyotypic instability, locus-specific gene rearrangements, and loss of heterozygosity at tumor suppressor loci - all of which can be recombinationally mediated. Genetic defects which increase the rate of somatic mutation (several of which feature elevated recombination) are associated with early incidence and high risk for a variety of cancers. Moreover, carcinogenic agents appear to quite consistently stimulate homologous recombination. If cells with high recombination arise, either spontaneously or in response to "recombinogens," and predispose to the development of cancer, what selective advantage could favor these cells prior to the occurrence of growth-promoting mutations? We propose that the augmentation of telomere-telomere recombination may provide just such an advantage, to hyper-recombinant cells within a population of telomerase-negative cells nearing their replicative (Hayflick) limit, by extending telomeres in some progeny cells and thus allowing their continued proliferation.