Identification of ras oncogene mutations in the stool of patients with curable colorectal tumors

Screening for colorectal cancer

In the past few years, knowledge of the clinical, biologic, and molecular genetic characteristics of colorectal cancer has greatly increased. Although the most cost-effective approach remains to be identified, screening for colorectal cancer can decrease mortality due to this disease by detecting cancers at earlier stages and allowing the removal of adenomas, thus preventing the subsequent development of cancer. Molecular studies that have helped define the genetic basis for this disease hold great promise for the development of better and more powerful methods to identify populations at risk. Individually, these technological, clinical, and basic-science advances are exciting; together, they promise to move us closer to the goal of substantially reducing mortality due to colorectal cancer.

Mutant K-ras in apparently normal mucosa of colorectal cancer patients. Its potential as a biomarker of colorectal tumorigenesis

BACKGROUND

The best way to reduce the incidence of colorectal cancer mortality would be to prevent this cancer. However, none of the biomarkers proposed can accurately identify persons at increased risk of colorectal cancer or those at low risk. As a possible genetic biomarker, K-ras mutations, which are frequently found in colorectal cancers, were analyzed in apparently normal colorectal mucosa.

METHODS

Nonneoplastic mucosa and tumor tissues were collected at surgery from 70 patients with colorectal cancer: one sample each from 50 patients (group A) and multiple samples from the other 20 patients (group B). Mutant K-ras codon 12 was analyzed by the enriched polymerase chain reaction (EPCR), by which one mutant can be detected among 10(3) to 10(4) normal alleles.

RESULTS

Only with the aid of EPCR was mutant K-ras detected in nonneoplastic mucosa of nine patients (18%) in Group A and five patients (25%) in Group B. This increased incidence could be attributed to the multiple tissue sampling. The presence of mutant K-ras in nonneoplastic mucosae was not consistently correlated with that in the tumors. These findings suggest that the mutant K-ras identified in nonneoplastic mucosa actually represents de novo mutations, which may be initiated by different etiologic factors and at different times.

CONCLUSION

Mutant K-ras detected in apparently normal mucosa should be a useful biomarker for identifying persons at higher risk of colorectal cancer. Our study also emphasizes the need for improving the method for sample collection to achieve true representation of the colorectal mucosa.

Faecal occult blood testing and colonoscopy in the surveillance of subjects at high risk of colorectal neoplasia

Colonoscopy is the established method of surveillance of subjects at high risk of developing colorectal neoplasia but the procedure is expensive, time consuming and occasionally hazardous. Faecal occult blood tests can be prepared at home and are cheap, simple and safe. Hemeselect is an immunological faecal occult blood test that is more sensitive for colorectal cancer than Haemoccult. The aim of this study was to determine the sensitivity of the Hemeselect test for asymptomatic colorectal neoplasia in subjects at high risk of the disease who were undergoing colonoscopy, thus assessing its suitability as an alternative means of screening high-risk groups. A total of 919 asymptomatic subjects were asked to complete Hemeselect tests. These were completed satisfactorily by 808 individuals (compliance rate 88 per cent) and were positive in 164 patients (20 per cent). At colonoscopy 11 cancers were detected in ten patients (seven Hemeselect positive) and 36 (16 Hemeselect positive) had at least one adenoma 1 cm or more in diameter. The test sensitivites of Hemeselect for carcinoma and large (1 cm or more) adenomas were 70 and 44 per cent respectively. In a subset of 417 subjects who also completed Haemoccult tests, the sensitivities were 33 and 18 per cent. Hemeselect specificity is 88 per cent compared with 98 per cent for Haemoccult. While the sensitivity of Hemeselect is higher than that of Haemoccult, it is still insufficient to replace colonoscopy in high-risk groups.

The murine N-ras gene is not essential for growth and development

The mammalian ras gene family encodes key cell-signaling, cell growth-related proteins that have been highly conserved in species from yeast to man. Specific point mutations in the ras genes are associated with various mammalian tumors. To understand the developmental role of the N-ras protooncogene in the mouse, we have disrupted its gene function by homologous recombination in embryonic stem cells. Mice derived from these cells that are homozygous for the N-ras mutation do not produce any detectable N-Ras protein and are morphologically and histologically indistinguishable from their heterozygous and wild-type siblings. Since N-ras is expressed at high levels in hematopoietic cells, we examined different populations of cells in peripheral blood and found no differences between mutant and normal animals. Our results show that N-ras gene function is dispensable for normal mouse development, growth, and fertility.

Molecular assessment of histopathological staging in squamous-cell carcinoma of the head and neck

BACKGROUND

Surgical oncologists rely heavily on the histopathological assessment of surgical margins to ensure total excision of the tumor in patients with head and neck cancer. However, current techniques may not detect small numbers of cancer cells at the margins of resection or in cervical lymph nodes.

METHODS

We used molecular techniques to determine whether clonal populations of infiltrating tumor cells harboring mutations of the p53 gene could be detected in histopathologically negative surgical margins and cervical lymph nodes of patients with squamous-cell carcinoma of the head and neck.

RESULTS

We identified 25 patients with primary squamous-cell carcinoma of the head and neck containing a p53 mutation who appeared to have had complete tumor resection on the basis of a negative histopathological assessment. In 13 of these 25 patients, molecular analysis was positive for a p53 mutation in at least one tumor margin. In 5 of 13 patients with positive margins by this method (38 percent), the carcinoma has recurred locally, as compared with none of 12 patients with negative margins (P = 0.02 by the log-rank test). Furthermore, molecular analysis identified neoplastic cells in 6 of 28 lymph nodes (21 percent) that were initially negative by histopathological assessment.

CONCLUSIONS

Among specimens initially believed to be negative by light microscopy, a substantial percentage of the surgical margins and lymph nodes from patients with squamous-cell carcinoma of the head and neck contained p53 mutations specific for the primary tumor. Patients with these positive margins appear to have a substantially increased risk of local recurrence. Molecular analysis of surgical margins and lymph nodes can augment standard histopathological assessment and may improve the prediction of local tumor recurrence.

A national population-based study of incidence of colorectal cancer and age. Implications for screening in older Americans

BACKGROUND

Population-based screening programs with flexible sigmoidoscopy have been advocated as a means to reduce the death rate from colorectal cancer. Because other studies have suggested a greater prevalence of lesions inaccessible to sigmoidoscopy in older patients, the expected yield of this procedure may differ in these subgroups.

METHODS

A 100% sample of Medicare beneficiaries 65 years or older with a first known diagnosis of colorectal cancer in 1987 was studied. Tumor site was divided into rectum, distal colon (distal to splenic flexure) and proximal colon. The analysis was also stratified by sex, race, and presence or absence metastatic disease, and incidence rates at each site by 5-year age group were calculated.

RESULTS

Among the 75,266 patients studied, the incidence of colorectal cancer increased from 1.59 patients/1000 in patients age 65-69 years to 3.87 patients/1000 in patients age 85 years and older. Although the incidence rates at all three sites increased, the increment was greatest for proximal tumors. The incidence trends with age also persisted in an analysis of only metastatic lesions. Moreover, incidence rates were consistently higher in men than in women and higher in whites than in blacks at all sites, though the age-related increase in incidence was consistent among all four groups.

CONCLUSIONS

The proportion of tumors beyond the reach of sigmoidoscopy increased with age, as did the actual incidence of accessible lesions. These patterns were also consistent in subgroup analyses. As the age-related increase in incidence was observed for metastatic tumors at all sites in the colon, age-related differences in screening and diagnostic evaluation alone do not adequately explain the findings. These data underscore the need for further studies of the relative benefits of cancer screening and pathogenic factors in tumor development in different subgroups of the older population.

Genetics of colon cancer: impact of inheritance on colon cancer risk

The genes that are mutated in two of the rare syndromes of hereditary colon cancer were recently identified, and genetic diagnosis is already possible in some cases. Acquired mutations of these same genes also appear to be important in sporadic colon cancers. Familial clustering of sporadic cases is common and may likewise arise from inherited susceptibility. Screening strategies for both the rare syndromes and the common cases of colon cancer with familial risk have been suggested. Certain clinical features allow stratification of colon cancer risk among common cases. It is anticipated that continued genetic investigation will result in more precise screening and improved diagnostic and therapeutic options for colon cancer.

Common occurrence of APC and K-ras gene mutations in the spectrum of colitis-associated neoplasias

BACKGROUND/AIMS

Chronic colitis is associated with an increased risk of colorectal neoplasia, creating a need for early diagnosis in this population. Little is yet known of the genetic changes of early lesions. Cases of colitis-associated neoplasia were analyzed for APC and K-ras mutations with special emphasis given to the spectrum of noninvasive lesions.

METHODS

Ten patients were studied. APC mutations were screened by an in vitro synthesized protein assay, and K-ras mutations were screened by a ligation assay.

RESULTS

APC mutations were found in 5 patients, including dysplasias. K-ras mutations were present in 5 patients and in all classes of lesions, including 5 of 14 lesions indefinite for dysplasia. In only 2 patients were no mutations found.

CONCLUSIONS

Mutations of APC and K-ras are common in colitis-associated neoplasia and can occur early in neoplastic progression. Serrated lesions and lesions indefinite for dysplasia may harbor genetic changes and thus are clonal, highlighting the importance of distinguishing them histologically. Assays for APC and K-ras mutations are promising as adjuncts to surveillance programs. Care will be needed in their application because the confident diagnosis of early lesions presumed to be of lesser clinical importance will raise new issues concerning prudent patient management.

Conservation genetics of the European brown bear--a study using excremental PCR of nuclear and mitochondrial sequences

In the Brenta area of northern Italy, a brown bear Ursus arctos population is rapidly going extinct. Restocking of the population is planned. In order to study the genetics of this highly vulnerable population with a minimum of stress to the animals we have developed a PCR-based method that allows the study of mitochondrial and nuclear gene sequences from droppings collected in the field. This method is generally applicable to animals in the wild. Using excremental as well as hair samples, we show that the Brenta population is monomorphic for one mitochondrial lineage and that female as well as male bears exist in the area. In addition, 70 samples from other parts of Europe were studied. As others have previously reported, the mitochondrial gene pool of European bears is divided into two major clades, one with a western and the other with an eastern distribution. Whereas populations generally belong to either one or the other mitochondrial clade, the Romanian population contains both clades. The bears in the Brenta belong to the western clade. The implications for the management of brown bears in the Brenta and elsewhere in Europe are discussed.

Detection of c-Ki-ras mutations in faecal samples from sporadic colorectal cancer patients

Colonic exfoliated epithelial cells in faecal material provide a source of human DNA which has been analysed for the presence of the tumour marker ras, in order to detect early tumour cells. The stool samples were subjected to a preliminary sample preparation step followed by centrifugation. DNA was extracted from both the centrifugation pellet and supernatant fractions, as well as from endoscopy washings, using a conventional phenol chloroform extraction method and was then purified on glass milk or spin columns. The purified DNA was amplified using mitochondrial primers and analysed for ras mutations using a non-radioactive, allele specific mismatch method. Corresponding tumour DNA was analysed for mutations using the same method. The results show that approximately 50% of the faecal samples analysed exhibited the presence of ras mutations which were also observed in the corresponding tumours. A double mutation was detected in one supernatant. Our findings represent an important stage in the development of a diagnostic test for the early detection of colorectal cancer.

Tumour diagnosis by PCR-based detection of tumour cells

Tumour cells shed from solid primary tumours can be detected by the polymerase chain reaction (PCR) based on the selective amplification of mutated tumour genes or of genes expressed in a tissue specific manner. When tumour specific alterations are amplified, few tumour cells can be detected in excess of normal cells derived from the same tissue. Thus, malignant cells can be detected specifically in pancreatic juice, stool, urine, and sputum. Here we describe the adaptation of the mutant enriched PCR in conjunction with the introduction of artificial primer mediated restriction sites to the selective amplification of mutant K-ras genes in stool samples from patients with colorectal carcinomas. In reconstitution experiments, down to 10 colorectal carcinoma cells could be detected in 100 mg of stool. For the diagnosis of micrometastatic disease, a sensitive and specific technique was established based on the reverse transcription of mRNA specific for the carcinoembryonic antigen followed by the amplification of the cDNA (RT-PCR). Attempts to establish a specific RT-PCR for cytokeratin-18 failed because of the existence of at least one processed pseudogene.

Molecular genetic tumor markers in the early diagnosis and screening of non-small-cell lung cancer

BACKGROUND

Little progress has been made in decreasing lung cancer mortality by applying conventional methods to early diagnosis and screening. Recent advances in molecular oncology, however, have provided tools which may be of use in this area. Many genes involved in controlling cell growth and differentiation are abnormal in lung cancer cells. Such genes include K-ras, p53, rb, myc, her2/neu, and probably one or more tumor suppressor genes on chromosome 3p. The involvement of these genes in lung cancer is reviewed. The K-ras oncogene contains a mutation in codon 12 in many cases of non-small-cell lung cancer, particularly adenocarcinoma, and is thus a potentially useful lung cancer tumor marker. DESIGN; We have developed a highly sensitive, simple assay for ras mutations, and applied it to bronchoalveolar lavage fluid obtained from patients undergoing evaluation for suspected lung cancer.

RESULTS

In many cases, the ras assay was more sensitive than routine cytology and histopathology, demonstrating that this is a potentially clinically useful assay.

CONCLUSION

Molecular genetic tumor markers, including mutations in ras and other genes, and/or immunohistochemical tumor markers, may provide tools which can be applied to bronchoalveolar lavage fluid or sputum, for use in diagnostic tests and in screening programs. The use of such markers may lead to decreased lung cancer mortality.

Cell cycle control and cancer

Multiple genetic changes occur during the evolution of normal cells into cancer cells. This evolution is facilitated in cancer cells by loss of fidelity in the processes that replicate, repair, and segregate the genome. Recent advances in our understanding of the cell cycle reveal how fidelity is normally achieved by the coordinated activity of cyclin-dependent kinases, checkpoint controls, and repair pathways and how this fidelity can be abrogated by specific genetic changes. These insights suggest molecular mechanisms for cellular transformation and may help to identify potential targets for improved cancer therapies.

Southwestern internal medicine conference: hereditary predisposition to colorectal cancer: new insights

Hereditary predisposition to colorectal cancer assumes two well-defined forms: familial adenomatous polyposis and hereditary nonpolyposis colon cancer. These tumors segregate as autosomal dominant conditions whose penetrance increases with age; cancer is expected to develop ultimately in as much as 50% of the offspring of affected individuals. These traits account for less than 1% and approximately 5% of all colorectal cancer, respectively. In addition, first-degree relatives of patients with common (sporadic) colorectal neoplasia are at increased risk of colorectal cancer. This relative risk averages approximately twofold but is significantly higher for relatives of younger patients (age at diagnosis, < 55 years). Familial adenomatous polyposis and a major subset of hereditary nonpolyposis colon cancer are due to loss-of-function germline mutations of genes located on chromosomes 5q and 2p, respectively. Both of these genes have been cloned recently. The gene affected in familial polyposis, APC, encodes a protein of unknown function that normally is found on the surface of maturing cells in the upper colonic crypts. The relevant gene in many hereditary nonpolyposis colon cancer kindreds is hMSH2. This gene encodes the human homologue of a bacterial protein MutS, which is part of a system known to repair base mismatches in newly replicated DNA. Loss of hMSH2 function may explain the strikingly erroneous replication of short DNA repeats (microsatellites) in colon tumors from patients with hereditary nonpolyposis colon cancer. Because this error-prone replication is found in approximately 13% of nonfamilial colon cancers, defective mismatch repair may contribute to the development of both hereditary and sporadic colon neoplasia. Molecular genetic assays to detect mutated alleles of these genes will facilitate presymptomatic identification of carriers in families with familial polyposis and hereditary nonpolyposis colon cancer. Current recommendations for surveillance of family members are presented in the light of the new genetic understanding of these diseases.

Gene mutations in saliva as molecular markers for head and neck squamous cell carcinomas

BACKGROUND

Cancer is caused by the accumulation of mutations that activate proto-oncogenes and inactivate tumor suppressor genes. The result is a clonal expansion of genetically identical daughter cells that eventually become clinical malignancies. The specific mutations acquired by the progenitor cell are like a fingerprint carried by each cell of the tumor. These mutations can serve as very specific markers for the presence of tumor cells in a background of normal cells.

METHODS

Mutations in the p53 gene recovered from head and neck squamous cell carcinomas were sequenced, and these altered DNA sequences were used retrospectively as tumor-specific genetic markers for cancer cells in the patient's saliva. Cloned p53 sequences amplified by the polymerase chain reaction from DNA extracted from banked preoperative saliva specimens were screened for the presence of tumor-specific mutations using radiolabeled oligonucleotide probes.

RESULTS

We identified tumor-specific mutations in preoperative saliva samples of 5 of the 7 patients evaluated (71%).

CONCLUSIONS

These results suggest a potential for clinical applications of this novel approach to cancer detection using gene mutations as molecular markers for carcinomas.

Microsatellite alterations as clonal markers for the detection of human cancer

Microsatellite instability has been reported to be an important feature of tumors from hereditary nonpolyposis colorectal carcinoma (HNPCC) patients. The recent discovery of genetic instability in small cell lung carcinoma, a neoplasm not associated with HNPCC, led us to investigate the possible presence of microsatellite alterations in other tumor types. We examined 52 microsatellite repeat sequences in the DNA of normal and tumor pairs from 100 head and neck, bladder, and lung cancer patients by the polymerase chain reaction. Although alterations were rare in dinucleotide repeats, larger (tri- or tetranucleotide) repeats were found to be more prone to expansion or deletion. We screened 100 tumors with a panel of nine tri- and tetranucleotide repeat markers and identified 26 (26%) that displayed alterations in at least one locus. This observation prompted us to examine the possibility of using microsatellite alterations as markers to detect clonal tumor-derived cell populations in pathologic samples. The identical microsatellite alterations detected in the primary tumors were successfully identified in corresponding urine, sputum, and surgical margins from affected patients. This study demonstrates that appropriately selected microsatellite loci are commonly altered in many cancers and can serve as clonal markers for their detection.

Nonsteroidal antiinflammatory agents in chemoprevention of colorectal cancer. At what cost?

The objective was to provide a comparison of the known toxicities of nonsteroidal antiinflammatory drugs (NSAIDS) and the likelihood of benefit from colorectal cancer (CRC) chemoprevention attributed to them. Chemoprevention trials require large numbers of subjects followed over many years and are therefore very expensive and difficult. Hence, it is important that agents tested in these trails have a realistic expectation of actual use in the population. Data sources were published literature on the toxicity and CRC chemopreventive activity of NSAIDS. Presently available NSAIDS, used at their usual therapeutic doses, have a serious toxicity rate that quickly exceeds any benefit from CRC prevention. In contrast, low-dose aspirin is worth evaluating, especially because of the potential for simultaneous cardiovascular risk reduction. Possibly, low doses of other NSAIDS may have benefit, but this remains unproven. Synthesis of other NSAIDS, with less toxicity, is another approach towards making the toxicity-benefit ratio more favorable for the use of these agents for CRC prevention.

Targeting cancer control: the state cancer control map and data program

The State Cancer Control Map and Data Program (National Technical Information Service, Springfield, Va) allows state and county mortality maps and data tables to be tailored according to the user's choice of cancer site, age, gender, race, county, and time period between 1953 and 1987. Counties and subpopulations within these maps and data tables that are identified as having exceptionally high rates of specific cancers can then be targeted for early detection or primary prevention. These maps and data tables provide a means for focusing state, local, and individual efforts to reduce cancer mortality in appropriate populations in areas with high mortality rates.

Prevalence of serum antibodies against the p53 tumor suppressor gene protein in various cancers

We have developed 2 new quantitative methods for measuring anti-p53 antibodies in human serum. Using these methods we analyzed 1,392 sera from patients with various malignancies and 230 sera from individuals without malignancy. Highest prevalence of anti-p53 antibodies was associated with ovarian and colon cancers (15%), followed by lung (8%) and breast (5%) cancers. Prevalence in other malignancies was lower (< 4%). In hospitalized patients and apparently healthy individuals, prevalence was very low (< 2 and 1% respectively). Extremely high antibody concentrations (> 10(5) U/L) were found in 5 ovarian, 2 breast, 1 lung and 1 colon cancers. Sequential analysis of 6 positive samples has shown that the p53 antibody test may have potential for patient monitoring. The p53 antibody-positive sera from breast cancer patients were associated with tumors that were steroid hormone receptor-negative (p < 0.002). We propose that the measurement of p53 antibodies is a relatively specific serological test for cancer, which can be performed with easily automatable and quantitative methodologies and may be further exploited for patient monitoring, prognosis, diagnosis and probably screening for selected cancers.

The case for colorectal cancer screening

There is strong evidence that sigmoidoscopic screening can reduce the risk of colorectal cancer mortality by as much as 70%, but the case for extensive fecal occult blood testing is less convincing. Flexible sigmoidoscopy performed once every five to 10 years in patients aged 50 to 75 appears to be warranted; however, many practical barriers to widespread implementation still need to addressed.

Molecular genetic profiles of colitis-associated neoplasms

BACKGROUND/AIMS

A major long-term risk for patients with chronic idiopathic colitis is the development of colorectal dysplasia and adenocarcinoma. The presence or absence of specific genetic changes in these lesions will provide important insights into the relationship of colitis-associated dysplasia and the development of carcinoma.

METHODS

A case-study approach was used to develop detailed molecular genetic profiles of advanced dysplasias and carcinomas from six patients with ulcerative colitis or Crohn's colitis.

RESULTS

Numerous genetic alterations were identified in each of the dysplasias and carcinomas profiled. These genetic alterations involved many of the same targets found in sporadic colorectal tumors and included multiple sites of allelic deletion, microsatellite instabilities, and mutations of the K-ras, p53, and APC genes. The progression of dysplasia to carcinoma was often accompanied by an accumulation of these mutations.

CONCLUSIONS

Genetic alterations are common in colitis-associated neoplasia, just as in sporadic colorectal neoplasia. This could have important implications for the evaluation and treatment of patients with colitis.

Diagnosis of pancreatic adenocarcinoma by polymerase chain reaction from pancreatic secretions

As mutations at codon 12 of the Ki-ras oncogene have been shown to occur in 90% of pancreatic adenocarcinomas, a novel strategy for the detection of these mutations in pancreatic secretions obtained at routine endoscopies was developed. Ki-ras DNA was amplified and screened for the presence of mutations at codon 12 with a combination of different rapid, non-radioactive molecular biology techniques. Examination of DNA from cell lines and paraffin-embedded tumour samples was used to establish and test the strategy employed. Pancreatic secretions from 27 patients were examined for the presence of Ki-ras mutations. Mutations at codon 12 were detected in 16/16 secretions from patients with histologically confirmed carcinoma and from one patient with carcinoma of the bile duct. In six patients a mutation identical to the one found in the pancreatic secretions was also demonstrated in paraffin-embedded fine-needle biopsy or surgical samples. Of the remaining ten patients (who had pancreatitis or cholelithiasis) mutations were not found in nine. Ki-ras codon 12 mutation was identified in one of these patients however, and mucous cell hyperplasia of pancreatic ducts was found upon histological examination. These findings establish Ki-ras polymerase chain reaction from pancreatic secretions as a valuable new diagnostic procedure for the demonstration of malignant cells, possibly at an early stage of the disease.

Allelic loss of chromosome 18q and prognosis in colorectal cancer

BACKGROUND

Colorectal cancer occurs in approximately 150,000 people each year in the United States. Prognostic assessment influences the treatment of patients with colorectal cancer, including decisions about adjuvant therapy. We evaluated chromosome 18q allelic loss, a genetic event associated with tumor progression, as a prognostic marker for this disease.

METHODS

We developed procedures to examine the status of chromosome 18q with microsatellite markers and DNA from formalin-fixed, paraffin-embedded tumors. Allelic loss of chromosome 18q was assessed in 145 consecutively resected stage II or III colorectal carcinomas.

RESULTS

Among patients with stage II disease, the five-year survival rate was 93 percent in those whose tumor had no evidence of allelic loss of chromosome 18q and 54 percent in those with allelic loss; among patients with stage III disease, survival was 52 and 38 percent, respectively. The overall estimated hazard ratio for death in patients whose tumor had chromosome 18q allelic loss was 2.83 (P = 0.008) according to univariate analysis. Furthermore, chromosome 18q allelic loss remained a strong predictive factor (hazard ratio for death, 2.46; 95 percent confidence interval, 1.06 to 5.71; P = 0.036) after adjustment for all other evaluated factors, including tumor differentiation, vein invasion, and TNM stage.

CONCLUSIONS

The status of chromosome 18q has strong prognostic value in patients with stage II colorectal cancer. The prognosis in patients with stage II cancer and chromosome 18q allelic loss is similar to that in patients with stage III cancer, who are thought to benefit from adjuvant therapy. In contrast, patients with stage II disease who do not have chromosome 18q allelic loss in their tumor have a survival rate similar to that of patients with stage I disease and may not require additional therapy.

Colorectal cancer: lessons for genetic counselling and care for families

Cancers of the colon and the rectum are the second leading cause of malignancy in European countries with similar incidence rates for men and women and, therefore, one of the major health concerns. Emphasis is placed on the early detection of a developing neoplasm in order to improve the life expectancy of patients and their quality of life. Colorectal cancer (CRC) is an excellent model for studying the etiology and pathogenesis of a common malignancy and the complex multistage process of carcinogenesis. Abundant clinical and pathological evidence suggests that CRC arises from benign adenomas that proceed through a series of steps to metastatic carcinomas. Following the discovery of oncogenes and, more importantly tumor suppressor genes, Fearon & Vogelstein (1990) proposed a scheme of genetic events which are associated with colorectal tumorigenesis. Genetic linkage studies have recently identified another type of gene for colon cancer susceptibility that seems to act by destabilising the genome.

Polymerase chain reaction-based methods for the detection of mutations in oncogenes and tumor suppressor genes

Altered expression of oncogenes and tumor suppressor genes, the normal function of which is to regulate cell growth and differentiation, represents a central event in the pathogenesis of human cancer. Aberrant expression of these genes is often a result of a mutational event. In vitro amplification of DNA with the polymerase chain reaction (PCR) has enormously increased the sensitivity of the methods to detect mutations. These PCR-based techniques have thus become invaluable in the elucidation of the mechanisms of carcinogenesis as well as in molecular genetics. In addition, the precise definition of a mutation at the molecular level can be a very valuable adjunct to the diagnosis and classification of malignancies as well as to their prognostic assessment. In this article several PCR-based strategies are outlined, their applicability in the detection of different types of mutations is discussed, and finally the application of these techniques in fresh and archival tissues is presented.

Dosage and allelic restriction fragment studies and PCR analysis of the H-ras locus in giant cell tumor of bone

Several studies have shown that giant cell tumor of bone frequently exhibits telomeric associations, commonly at chromosome 11p, which is also the location of the H-ras oncogene. In addition, rare H-ras alleles are more common among cancer patients than among healthy controls and point mutations of this oncogene have also been reported in several malignancies. These data led us to investigate gene dosage, restriction fragment-length size, and point mutations for H-ras in giant cell tumor of bone. Quantitative Southern blot analysis revealed no amplification of the H-ras oncogene in tumor DNA compared with DNA from peripheral blood in the same patient or from control subjects. In addition, no point mutations were detected in codons 12, 13, or 61 (mutations of these codons have been reported in other neoplasms) of the H-ras gene. No differences were noted in restriction fragment-length polymorphisms between tumor and peripheral blood in the same patient and no loss of heterozygosity was detected. In addition, there was no increased frequency of rare H-ras alleles (8% of alleles) in giant cell tumor patients compared to controls (21% of alleles) in our study. However, large allele sizes (> 8.5 kb) were significantly overrepresented in GCT patients compared with healthy controls. In our study, three of 12 alleles were found to be rare in the healthy controls but were common among GCT patients. Our data suggest that the H-ras oncogene is unlikely to be the site of a biologically significant primary lesion in GCT tumorigenesis.

Do characteristics of adenomas on flexible sigmoidoscopy predict advanced lesions on baseline colonoscopy?

BACKGROUND/AIMS

Colonoscopy is presently recommended for patients with any benign neoplasm found on sigmoidoscopy. The purpose of this study was to determine whether characteristics of adenomas on flexible sigmoidoscopy predict advanced lesions on baseline colonoscopy.

METHODS

A total of 226 asymptomatic and symptomatic patients with adenomas noted on flexible sigmoidoscopy at a large, multispecialty medical group were prospectively studied. The histology, size, and number of benign polyps on flexible sigmoidoscopy were compared with those on subsequent colonoscopy. Advanced lesions were defined as adenomas > 1 cm in diameter or with villous or severe dysplasia histology. Univariate comparisons were assessed using the chi 2 test and multivariate analysis with stepwise logistic regression.

RESULTS

There was a 24% prevalence of new adenomas found on colonoscopy. Six percent of the patients had advanced lesions on colonoscopy, and none had cancer. Multivariate analysis indicated that findings on flexible sigmoidoscopy predict (P < 0.01) those on colonoscopy. Patients with advanced lesions on sigmoidoscopy had a > 10% prevalence of an advanced lesion on colonoscopy. Patients with small (< or = 1 cm) tubular adenoma(s) on sigmoidoscopy had a < 1% occurrence of an advanced synchronous lesion.

CONCLUSIONS

The histology and size of benign neoplasms found on flexible sigmoidoscopy predict findings on baseline colonoscopy.

Chromosome allele loss in colorectal liver metastases and its association with clinical features

Molecular genetic changes are better characterized in colorectal carcinoma than in other common adult tumours. Consistent allele losses, or loss of heterozygosity (LOH), on chromosomes 5q, 17p and 18q have been well established. These changes are associated with the prognosis of the disease. Little is known of such changes in liver metastases of colorectal origin. The extent of allelic loss and its association with clinical features were investigated in 19 patients with colorectal liver metastases by using 24 probes to detect restriction fragment length polymorphism. A high frequency of LOH on chromosomes 5q, 17p and 18q was found in these secondary tumours. No consistent loss has so far been shown in any other chromosome. The frequency of allele loss correlated significantly with prognostic features such as the number and size of liver secondaries (P < 0.005), metastasis to the lymph nodes (P < 0.01) and curative or palliative operation (P < 0.02).

Two-dimensional electrophoretic analysis of proteins expressed by normal and cancerous human crypts: application of mass spectrometry to peptide-mass fingerprinting

Protein patterns of normal human colonic crypts, isolated from different regions of the large intestine, and several colorectal cancer cell lines were compared using two-dimensional electrophoresis gels (2-DE). As detected by intrinsic radiolabeling and Coomassie Brilliant Blue staining, the protein patterns for normal crypts isolated from the ascending, and descending, regions of the colon and the rectum, were almost (> 95%) identical. While 75-80% of the protein spots from normal crypts and the colorectal cancer cell line (LIM 1863), a cell line that grows as organoids and differentiates spontaneously into crypt-like structures in vitro, can be matched, the relative expression levels of a large number of proteins differ. At least two protein spots (undetectable in the protein pattern from normal cells), proteins a (M(r) approximately 18,000, pI 6.7-6.9) and b (M(r) approximately 24,000, pI 5.9-6.0), were detected in the 2-DE gel protein pattern in the three cell lines LIM 1863, LIM 1215 and LIM 1899. The identity of these proteins is not yet known and further studies are required before they can be considered as potential colon tumor markers. Approximately 60% of the cellular proteins from LIM 1215 cells, a colon carcinoma cell line that exhibits many properties associated with columnar cells, can be matched with LIM 1863 cells. The results presented here represent an initial phase in our efforts to develop a comprehensive protein database for normal human colon cells and several colorectal cancer cell lines. While our initial protein identification relied on microsequencing methodologies, we are presently evaluating peptide-mass fingerprinting, utilizing capillary reversed-phase high-performance liquid chromatography (RP-HPLC) and electrospray mass spectrometry, as a means for rapid identification of proteins at subpicomole levels. Using this approach, protein #3 (M(r) approximately 66,000, pI 6.2) was identified as heat shock protein 60 from as few as seven tryptic peptide masses when they were screened against the molecular weight search (MOWSE) peptide-mass database.

Colorectal carcinoma: current problems and future perspectives

Colorectal carcinoma represents a highly interesting model for the biological development of a solid tumor, the efficacy or primary and secondary prevention and the development of chemotherapeutic and immunologic strategies for adjuvant and/or neoadjuvant treatment is resectable stages. Adjuvant systemic 5-FU/levamisole is currently the standard adjuvant treatment for stage III colon cancer. 5-FU/folinic acid for 6 months seems to achieve equivalent results. Continuous infusion of 5-FU for 7 days postoperatively via the portal vein achieves also a comparable improvement in disease-free and overall survival. Beyond the long term systemic as well as short time intraportal chemotherapy, adjuvant immunotherapy with either 17-1A murine monoclonal antibody or autologous tumor vaccine achieves quite comparable results like adjuvant chemotherapy. Therefore the combination of these modalities might be of high interest for further investigation. The current EORTC study for colorectal cancer investigates the role of the combination of short time regional and long term systemic chemotherapy. For rectal cancer stage II and III adjuvant 5-FU plus radiation is currently the standard. However, further improvement seems possible with 5-FU given as continuous infusion during radiation; this approach is currently investigated in an ongoing Intergroup study. A further attractive approach, particularly for locally advanced, borderline resectable rectal cancer is the neoadjuvant combined modality treatment with 5-FU/folinic acid plus radiation followed by surgery and further adjuvant chemotherapy; this neoadjuvant treatment is currently being investigated in comparison to postoperative 5-FU/folinic acid plus radiation in an ongoing Intergroup study. Future protocols should also include immunotherapy with 17-1A antibody which significantly prolongs disease-free and overall survival also in rectal cancer.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemoprevention of cancer

Chemoprevention is a strategy used to block the development of cancers in human beings. This emerging field has broad potential for influencing cancer incidence rates in defined high-risk groups and the general population. In this review, we define some of the mechanisms of carcinogenesis, describe some of the genetic markers of carcinogenesis, and list possible biomarkers that may serve as surrogate end points in chemoprevention studies. A major component of this review is a description of the agents that are currently under investigation in animal systems or in human trials. They are grouped according to the agents that block or suppress mutation, such as oltipraz, selenium, vitamin C and the flavones, or according to agents that block promotion and proliferation, such as difluoromethylornithine, tamoxifen, nonsteroidal antiinflammatory drugs, and the vitamin A derivatives. We describe the issues that are considered in the design of chemoprevention trials and in the phase I, II, and III components of these trials. The following national trials are discussed: the Breast Cancer Prevention Trial, which uses tamoxifen; the Prostate Cancer Prevention Trial, which uses finasteride; and a Lung Cancer Prevention Trial, which uses 13-cis-retinoic acid. The review ends with some insights about future studies in chemoprevention.

Mutation detection by denaturing gradient gel electrophoresis (DGGE)

The molecular analysis of genetic diseases relies on several technical approaches which allow genetic and physical mapping, characterization of the gene structure, expression studies, and identification of disease-causing mutations. Denaturing gradient gel electrophoresis (DGGE) allows the rapid screening for single base changes in enzymatically amplified DNA. The technique is based on the migration of double-stranded DNA molecules through polyacrylamide gels containing linearly increasing concentrations of a denaturing agent. In this review DGGE and the several modifications of the original protocol are presented. Moreover, its applications in human molecular genetics are summarized together with a preliminary comparison with other mutation detection technologies such as chemical cleavage, RNase protection, and single-strand conformation polymorphism.

Detection of point mutations by solid-phase methods

Several techniques exist that permit the efficient distinction among characterized DNA sequence variants. In this review we discuss a number of such analytic procedures. These techniques all take advantage of a variety solid supports to prepare and analyze reaction products. The described diagnostic principles are now being applied for the development of miniaturized assay formats, suitable for automated detection of large sets of sequences in clinical samples.

Reflections on the cost consequences of the new gene technology for health policy

This article presents a preliminary and necessarily tentative and subjective assessment of the impact of new gene technology on health care costs. In the short term, diagnosis and treatment of genetic disease are likely to increase costs. Treatment with nongene therapy will continue to be far less expensive than gene therapy where it is available. Research developments to monitor as indicators of forthcoming cost reductions in genetic therapy are set forth. Some forms of genetic screening may soon reduce health care costs, and an example is provided. Genetically engineered pharmaceuticals are described and their impact on costs reviewed. Conditions under which they are likely to reduce health care costs are indicated.

Cytometric validation of immunocytochemical observations in developing lung cancer

Video-enhanced optical microscopy objectively confirms that immunocytochemical biomarker supplementation of routine cytology permits separation of (1) "pre"-cancer epithelial cells from JHLP screened individuals who subsequently developed lung cancer from (2) similarly atypical epithelial cells from JHLP participants who did not. The establishment of a bank of sputum cytology specimens along with a data respository of 5-yr follow-up and clinical outcome had permitted banked specimens to be immunostained and scored against a gold standard of subsequent histologic lung cancer. A highly skilled cytopathologist, interpreting immunostained screening sputum specimens and blinded to the clinical outcome, originally was able to correctly predict clinical outcome with 88.7% accuracy compared to this "gold standard" (Tockman et al., J Clin Oncol 1988;6:1685-1693). This study presents an independent confirmation of that earlier immunocytochemical classification through feature extraction of digitally recorded, transmission optical microscope video images of immunostained, moderately atypical sputum cells from the original slides.

Mucosal origin and shedding of an early colonic tumor marker defined by Adnab-9 monoclonal antibody

Recent attention has been drawn to the diagnostic potential of tests based on shed colonic tumor markers. Adnab-9 monoclonal antibody raised against neoplastic, potentially premalignant colonic adenomas recognizes a marker in colonic effluent or tissue which correlates with the presence of tumors or risk of colorectal cancer. The origin of this antigen and optimal collection of colonic effluent were investigated by enzyme-linked immunosorbent assay and Western blotting. Mean Adnab-9 binding in effluent samples from colorectal cancer patients even after resection is high as compared with that in normal subjects (P < 0.05). Effluent samples are best collected in the morning hours. Antigen proteolysis may be significant depending on the site and timing of effluent collection, but breakdown products are reactive. Tissue and effluent Adnab-9 binding at any one anatomic site of collection appear to correlate (r = 0.88, P = 0.01). The Adnab-9 antigen is constitutively expressed at low levels throughout the distal bowel and localized to the deepest regions of the mucosal crypts. Other than meconium, no significant levels of binding are found in other body fluids. This antigen is specific for the gastrointestinal tract, its binding in conveniently collected effluent samples correlates with tissue content, and the antigen is constitutively expressed in the crypts of the distal small bowel and colonic mucosa.

Genetics, molecular biology and colorectal cancer

Colorectal cancer (CRC) develops through several histologically well-defined stages, reflecting the sequential acquisition of genetic alterations. Several frequently mutated genes have been identified which probably contribute to the development of both hereditary and sporadic cancer (reviewed in Bishop and Thomas, 1990; Fearon and Vogelstein, 1990; Fearon and Jones, 1992; Hamilton, 1992). Several generalizations emerge from this work. Mutations are observed in the earliest detectable stages of cancer development. Specific genes tend to be mutated in a given order, but it is the accumulation of a critical number of lesions which governs the appearance of neoplasia. Mutations actively promote neoplastic character by activating oncogenes and eliminate restraints on neoplastic character by inactivating tumour suppressor genes.

Diet and the prevention of colorectal cancer

It is important for those working in the area of health-promotion that consensus be reached on the role of diet in colorectal cancer and its etiology. In developing health-promotion strategies, further research is needed into the beliefs, attitudes and behaviour of different groups. More qualitative data on the diet of different groups in the community is also needed. Further basic research on the role of diet in this cancer requires that biomarkers be related to human or animal dietary exposures. The development of new animal and human models may be appropriate.