Options for screening for colorectal cancer

Distribution of colorectal polyps: Implications for screening

BACKGROUND

During the last decades data from different studies reported modifications of the topographic distribution of colorectal cancers (CRCs), with an increased frequency of tumours in proximal colonic segments. Given the documented link between adenomas and CRC, a proximal migration of adenomas over time could be expected as well.

AIM

To evaluate available evidence about the prevalence of adenomas and of sessile serrated polyps across colonic segments, the changing trends in their distribution across the colon and the diagnostic performance of screening tests currently adopted in population based screening programs for lesions located in different colonic segments.

METHODS

Literature search on PubMed, Embase, and Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects with reference to preferred reporting items for systematic reviews and meta-analysis (PRISMA), considering all adult human studies in English, published between January 2000 and February 2017.

RESULTS

Cross-sectional analysis of endoscopy and pathology data-bases are consistently showing a trend toward an increase with age of the proportion of adenomas located in the proximal colon. Several observational studies analysed the site distribution of adenomas, testing the hypothesis of a proximal shift of these lesions, and most of them reported an increase in the proportion of right-sided adenomas over time, although a similar trend was not confirmed by others. Also the quality of the retrieved evidence was low. Both endoscopy and FIT are showing a different level of sensitivity for lesions arising in different colonic segments, depending also on screenees characteristics.

CONCLUSION

Available evidence is supporting the hypothesis of an increase in the proportion of right-sided adenomas with age, while a similar increase has not been reported for SSP/A, at least among subjects aged 50 or older. The trend toward a proximalization of colorectal adenomas over time, reported by some authors, likely results from improved diagnostic performances and/or the process of population ageing.

Epigenetic silencing of protocadherin 10 in colorectal cancer

Colorectal cancer (CRC) is one of the most common types of malignant tumor in the world and occurs through a multi-step process resulting from the accumulation of genetic and epigenetic alterations of the genome. Although the molecular mechanisms of the pathogenesis of CRC remain unclear, the inactivation of tumor suppressor genes (TSGs) through promoter methylation serves an important role. Aberrant methylation is a well-defined marker of CRC. At present, the epigenetic silencing of protocadherin 10 (PCDH10) has been identified as an important TSG with key roles in colorectal carcinogenesis, invasion and metastasis as a frequent and early event. Advances in gene methylation detection in tumor tissues and body fluids have led to the development of non-invasive screening methods for CRC. The present study aimed to review the epigenetic alteration of PCDH10 in CRC development, and the potential of PCDH10 to be a non-invasive biomarker for CRC.

Prevention of colorectal cancer: How many tools do we have in our basket?

Prevention is the main strategy in order to reduce colorectal cancer incidence and mortality. It can be accomplished through primary prevention, using measures affecting factors known to confer higher risk of colorectal cancer, or through secondary prevention, aimed at early diagnosis of cancer or preneoplastic lesions in groups of subjects at increased risk of cancer. Although primary prevention should be the goal for future years, because it acts on the probable causes of colorectal cancer, at present it seems that secondary prevention is more effective on colorectal cancer survival, and the approaches which have yielded the most satisfying results, in terms of reduced mortality for cancer, are those aimed at detecting preneoplastic lesions, or cancer at an early stage in selected groups of subjects at average or increased risk of colorectal cancer. These groups are subjects aged 50years or older, affected individuals (gene carriers) or family members of hereditary colorectal cancer syndromes (i.e., Lynch syndrome and familial adenomatous polyposis), and patients with inflammatory bowel diseases. The most effective procedures used, though with some drawbacks, are fecal occult blood tests and colonoscopy. Future research should be addressed to find new approaches that will render preventive strategies more acceptable for the population, and more cost-effective.

Meta-analysis of the association between APC promoter methylation and colorectal cancer

Previous studies investigating the association between adenomatous polyposis coli (APC) gene promoter methylation and colorectal cancer (CRC) have yielded conflicting results. The aim of this study was to comprehensively evaluate the potential application of the detection of APC promoter methylation to the prevention and treatment of CRC. PubMed, Embase, and MEDLINE (results updated to October 2014) were searched for relevant studies. The effect size was defined as the weighted odds ratio (OR), which was calculated using either the fixed-effects or random-effects model. Prespecified subgroup and sensitivity analyses were conducted to evaluate potential heterogeneity among the included studies. Nineteen studies comprising 2,426 participants were selected for our meta-analysis. The pooled results of nine studies comprising a total of 740 subjects indicated that APC promoter methylation was significantly associated with CRC risk (pooled OR 5.53; 95% confidence interval [CI] 3.50–8.76; P<0.01). Eleven studies with a total of 1,219 patients evaluated the association between APC promoter methylation and the presence of CRC metastasis, and the pooled OR was 0.80 (95% CI 0.44–1.46; P=0.47). A meta-analysis conducted with four studies with a total of 467 patients found no significant correlation between APC promoter methylation and the presence of colorectal adenoma (pooled OR 1.85; 95% CI 0.67–5.10; P=0.23). No significant correlation between APC promoter methylation and patients’ Dukes’ stage, TNM stage, differentiation grade, age, or sex was identified. In conclusion, APC promoter methylation was found to be significantly associated with a higher risk of developing CRC. The findings indicate that APC promoter methylation may be a potential biomarker for the carcinogenesis of CRC.

DNA methylation as an epigenetic biomarker in colorectal cancer

Sporadic colorectal cancer (CRC) is a consequence of the accumulation of genetic and epigenetic alterations that result in the transformation of normal colonic epithelial cells to adenocarcinomas. Studies have indicated that a common event in the tumorigenesis of CRC is the association of global hypomethylation with discrete hypermethylation at the promoter regions of specific genes that are involved in cell cycle regulation, DNA repair, apoptosis, angiogenesis, adhesion and invasion. The present study aimed to investigate the epigenetic changes (DNA methylation) in 24 candidate genes in CRC. A total of 10 candidate hypermethylated (HM) and unmethylated (UM) genes were identified that may be useful epigenetic markers for non-invasive CRC screening. The five genes that had the highest average UM percentages in the control group were MLH1 (71.7%), DKK2 (69.6%), CDKN2A (68.4%), APC (67.5%) and hsa-mir-342 (67.4%). RUNX3 (58.9%), PCDH10 (55.5%), SFRP5 (52.1%), IGF2 (50.4%) and Hnf1b (50.0%) were the five genes with the highest average HM percentages in the test group. In summary, the present preliminary study identified the methylation profiles of normal and cancerous colonic epithelial tissues, and provided the groundwork for future large-scale methylation studies.

DNA methylation based biomarkers: practical considerations and applications

A biomarker is a molecular target analyzed in a qualitative or quantitative manner to detect and diagnose the presence of a disease, to predict the outcome and the response to a specific treatment allowing personalized tailoring of patient management. Biomarkers can belong to different types of biochemical molecules such as proteins, DNA, RNA or lipids, whereby protein biomarkers have been the most extensively studied and used, notably in blood-based protein quantification tests or immunohistochemistry. The rise of interest in epigenetic mechanisms has allowed the identification of a new type of biomarker, DNA methylation, which is of great potential for many applications. This stable and heritable covalent modification mostly affects cytosines in the context of a CpG dinucleotide in humans. It can be detected and quantified by a number of technologies including genome-wide screening methods as well as locus- or gene-specific high-resolution analysis in different types of samples such as frozen tissues and FFPE samples, but also in body fluids such as urine, plasma, and serum obtained through non-invasive procedures. In some cases, DNA methylation based biomarkers have proven to be more specific and sensitive than commonly used protein biomarkers, which could clearly justify their use in clinics. However, very few of them are at the moment used in clinics and even less commercial tests are currently available. The objective of this review is to discuss the advantages of DNA methylation as a biomarker, the practical considerations for their development, and their use in disease detection, prediction of outcome or treatment response, through multiple examples mainly focusing on cancer, but also to evoke their potential for complex diseases and prenatal diagnostics.

Self-stabilizing colonic capsule endoscopy: pilot study of acute canine models

Video capsule endoscopy (VCE) is a noninvasive method for examining the gastrointestinal tract which has been successful in small intestine studies. Recently, VCE has been attempted in the colon. However, the capsule often tumbles in the wider colonic lumen, resulting in missed regions. Self-stabilizing VCE is a novel method to visualize the colon without tumbling. The aim of the present study was to comparatively quantify the effect of stabilization of a commercially available nonmodified capsule endoscope (CE) MiroCam and its modified self-stabilizing version in acute canine experiments. Two customized MiroCam CEs were reduced in volume at the nonimaging back-end to allow the attachment of a self-expanding, biocompatible stabilizing device. Four mongrel dogs underwent laparotomy and exteriorization of a 15-cm segment of the proximal descending colon. A single CE, either self-stabilizing or nonmodified was inserted through an incision into the lumen of the colon followed by pharmacologically induced colonic peristalsis. The inserted capsule was propelled distally through the colon and expelled naturally through the anus. Novel signal processing method was developed to quantify the video stabilization based on camera tracking a predetermined target point (locale). The average locale trajectory, the average radius movement of the locale, and the maximum rate of change of the locale for sequential images were significantly lower for the stabilized capsules compared to the nonstabilized ones . The feasibility of self-stabilized capsule endoscopy has been demonstrated in acute canine experiments.

Colorectal cancer screening comparing no screening, immunochemical and guaiac fecal occult blood tests: a cost-effectiveness analysis

Comparability of cost-effectiveness of colorectal cancer (CRC) screening strategies is limited if heterogeneous study data are combined. We analyzed prospective empirical data from a randomized-controlled trial to compare cost-effectiveness of screening with either one round of immunochemical fecal occult blood testing (I-FOBT; OC-Sensor®), one round of guaiac FOBT (G-FOBT; Hemoccult-II®) or no screening in Dutch aged 50 to 75 years, completed with cancer registry and literature data, from a third-party payer perspective in a Markov model with first- and second-order Monte Carlo simulation. Costs were measured in Euros (€), effects in life-years gained, and both were discounted with 3%. Uncertainty surrounding important parameters was analyzed. I-FOBT dominated the alternatives: after one round of I-FOBT screening, a hypothetical person would on average gain 0.003 life-years and save the health care system €27 compared with G-FOBT and 0.003 life years and €72 compared with no screening. Overall, in 4,460,265 Dutch aged 50-75 years, after one round I-FOBT screening, 13,400 life-years and €320 million would have been saved compared with no screening. I-FOBT also dominated in sensitivity analyses, varying uncertainty surrounding important effect and cost parameters. CRC screening with I-FOBT dominated G-FOBT and no screening with or without accounting for uncertainty.

Correlation between preoperative endoscopic and intraoperative findings in localizing colorectal lesions

BACKGROUND

Colonoscopy findings compared with findings at time of surgery have a discrepancy rate of 3-21%. The objective of our study was to investigate this discrepancy and provide potential resolutions.

METHODS

In this retrospective study, we identified 400 patients who underwent colonoscopy followed by colon resection at our community hospitals in 1999-2006. Discrepancies between colonoscopy and intraoperative findings were noted. Each discrepancy was classified as major if the surgical procedure had to be altered, the lesion was missed, an unnecessary segment was removed, or the incision was extended. A discrepancy was classified as minor if there was no alteration in planned surgery.

RESULTS

Of the 400 cases, 160 (40%) were located in the right colon, 13 (3%) were in the transverse colon, 185 (46%) were in the left colon, and 42 (11%) were in the rectum. A total of 48 (12%) discrepancies between colonoscopy and intraoperative findings were identified: 26 (54%) were major and 22 (46%) were minor. Thirteen (27%) were in the proximal colon (3 major and 10 minor discrepancies), 3 (6.3%) were in the transverse colon (all major), 22 (46%) were in the distal colon (17 major and 5 minor), and 10 (21%) were in the rectum (3 major, 7 minor). Major discrepancies were significantly higher in the left colon (17 of the 185 left-sided lesions; 9.1%) than in the right colon (3/160; 1.9%; P = 0.045).

CONCLUSIONS

In our study, colonoscopy has an error rate of 12% when used to localize tumors; more than half of these patients require significant unanticipated changes in their surgery. The discrepancies are significantly higher in left side of colon.

The utility and predictive value of combinations of low penetrance genes for screening and risk prediction of colorectal cancer

Despite the fact that colorectal cancer (CRC) is a highly treatable form of cancer if detected early, a very low proportion of the eligible population undergoes screening for this form of cancer. Integrating a genomic screening profile as a component of existing screening programs for CRC could potentially improve the effectiveness of population screening by allowing the assignment of individuals to different types and intensities of screening and also by potentially increasing the uptake of existing screening programs. We evaluated the utility and predictive value of genomic profiling as applied to CRC, and as a potential component of a population-based cancer screening program. We generated simulated data representing a typical North American population including a variety of genetic profiles, with a range of relative risks and prevalences for individual risk genes. We then used these data to estimate parameters characterizing the predictive value of a logistic regression model built on genetic markers for CRC. Meta-analyses of genetic associations with CRC were used in building science to inform the simulation work, and to select genetic variants to include in logistic regression model-building using data from the ARCTIC study in Ontario, which included 1,200 CRC cases and a similar number of cancer-free population-based controls. Our simulations demonstrate that for reasonable assumptions involving modest relative risks for individual genetic variants, that substantial predictive power can be achieved when risk variants are common (e.g., prevalence > 20%) and data for enough risk variants are available (e.g., ~140–160). Pilot work in population data shows modest, but statistically significant predictive utility for a small collection of risk variants, smaller in effect than age and gender alone in predicting an individual’s CRC risk. Further genotyping and many more samples will be required, and indeed the discovery of many more risk loci associated with CRC before the question of the potential utility of germline genomic profiling can be definitively answered.

Genomic and oncoproteomic advances in detection and treatment of colorectal cancer

Aims

We will examine the latest advances in genomic and proteomic laboratory technology. Through an extensive literature review we aim to critically appraise those studies which have utilized these latest technologies and ascertain their potential to identify clinically useful biomarkers.

Methods

An extensive review of the literature was carried out in both online medical journals and through the Royal College of Surgeons in Ireland library.

Results

Laboratory technology has advanced in the fields of genomics and oncoproteomics. Gene expression profiling with DNA microarray technology has allowed us to begin genetic profiling of colorectal cancer tissue. The response to chemotherapy can differ amongst individual tumors. For the first time researchers have begun to isolate and identify the genes responsible. New laboratory techniques allow us to isolate proteins preferentially expressed in colorectal cancer tissue. This could potentially lead to identification of a clinically useful protein biomarker in colorectal cancer screening and treatment.

Conclusion

If a set of discriminating genes could be used for characterization and prediction of chemotherapeutic response, an individualized tailored therapeutic regime could become the standard of care for those undergoing systemic treatment for colorectal cancer. New laboratory techniques of protein identification may eventually allow identification of a clinically useful biomarker that could be used for screening and treatment. At present however, both expression of different gene signatures and isolation of various protein peaks has been limited by study size. Independent multi-centre correlation of results with larger sample sizes is needed to allow translation into clinical practice.

Screening for Rectal Cancer – Will it Improve Cure Rates?

Here we give an overview of colorectal cancer screening strategies with an emphasis on the diagnosis and management of rectal cancer. We review the published studies on screening in the high-risk population, including patients with a history of colorectal cancer, inflammatory bowel disease and inherited conditions. In the average-risk population, the evidence base for a number of screening strategies is evaluated, including endoscopy, contrast studies and faecal occult blood testing. Screening guidelines in the high-risk population are predominantly based on case-control studies comparing the incidence of colorectal cancer in screened and control groups. Screening the average-risk population for colorectal cancer reduces cancer-specific mortality by 15% after biennial guaiac faecal occult blood testing and 50-80% after flexible sigmoidoscopy. All of the screening strategies outlined have a greater sensitivity for distal lesions than proximal lesions.

Factors related to incomplete flexible sigmoidoscopy among adult Chinese in Taiwan

BACKGROUND

Sigmoidoscopy is effective in colorectal cancer screening, but incomplete examinations may overlook colonic pathologies and delay diagnosis. This study aimed to explore risk factors for incomplete insertions of flexible sigmoidoscopy among Taiwanese.

METHODS

Healthy adults participating in health check-up in a tertiary medical center were invited for study. Subjects were recruited when they had fully consented and agreed to participate. Factors related to incomplete insertions of flexible sigmoidoscopy were evaluated and multivariate logistic regression was used to determine independent risk factors. A predictive model was generated by the risk factors identified.

RESULTS

In total, 1,252 subjects (mean age, 53.9 13.1 years; age range, 2187 years; male/female,780/472) were enrolled, and 278 (22.2%) incomplete insertions were recorded. Multivariate analysis showed that female gender (odds ratio [OR], 2.06; 95% confidence interval [CI], 1.562.73; p < 0.001), age >or= 60 years (OR, 1.68; 95% CI, 1.262.23; p < 0.001), inadequate bowel preparation (OR, 1.66; 95% CI, 1.212.16; p = 0.001), history of constipation (OR, 2.43; 95% CI, 1.045.69; p = 0.042), and body mass index (BMI) < 25 kg/m2 (OR, 1.41; 95% CI, 1.051.89; p = 0.024) were all independent risk factors. The probability of incomplete insertion was significantly associated with the sum of the aforementioned risk factors (p < 0.001). Compared with subjects with no risk factors, the risks of incomplete insertions increased significantly among subjects bearing 1 risk factor (OR, 2.57; 95% CI, 1.474.49; p = 0.001), 2 risk factors (OR, 4.41; 95% CI, 2.527.39; p < 0.001), 3 risk factors (OR, 6.40; 95% CI, 3.5611.52; p < 0.001) and >or= 4 risk factors (OR, 10.00; 95% CI, 3.8925.70; p < 0.001).

CONCLUSION

Female sex, age >or= 60 years, BMI < 25 kg/m2, history of constipation, and inadequate bowel preparation were independent risk factors for incomplete insertion of flexible sigmoidoscopy. Subjects with multiple risk factors may consider alternative modalities for colonic examination.

Uptake of population-based flexible sigmoidoscopy screening for colorectal cancer: a nurse-led feasibility study

OBJECTIVE

To assess uptake of once-only flexible sigmoidoscopy (FS) in a community sample to determine whether FS would be viable as a method of population-based screening for colorectal cancer.

METHODS

All adults aged 60-64 years registered at three General Practices in North West London, UK (510 men and women) were sent a letter of invitation to attend FS screening carried out by an experienced nurse, followed by a reminder if they did not make contact to confirm or decline the invitation. The primary outcome was attendance at the endoscopy unit for a FS test.

RESULTS

Of the 510 people invited to attend, 280 (55%) underwent FS. Among non-attenders, 91 (18%) were ineligible for screening or did not receive the invitation, 19 (4%) accepted the offer of screening but were unable to attend during the study period, 52 (10%) declined the offer, 41 (8%) did not respond to the invitation, and 27 (5%) accepted the offer of screening but did not attend. Attendance among those eligible to be screened, who had received the invitation, was 67%. People from more socioeconomically deprived neighbourhoods were less likely to attend (odds ratio [OR] = 0.90; confidence interval [CI] = 0.84-0.96; P = 0.003). Women were more likely to attend than men (OR = 1.44; CI = 1.01-2.05; P = 0.041).

CONCLUSIONS

Attendance rates in this pilot for nurse-led, population-based FS screening were higher than those reported in other FS studies, and comparable with adherence to fecal occult blood testing (FOBT) in the UK FOBT pilot. Having a female nurse endoscopist may have been responsible for increasing female uptake rates but this warrants confirmation in a larger study.

Correlation of K-ras codon 12 mutations in human feces and ages of patients with colorectal cancer (CRC)

Colorectal cancer (CRC) is the predominant gastrointestinal malignancy and constitutes a major medical and economic burden worldwide. A thorough understanding of the oncogenes or genes related to tumorigenesis is the key to developing successful therapeutic strategies. Molecular analysis of feces constitutes a potentially potent and noninvasive method for detection of CRC. Using nested reverse transcription-polymerase chain reaction (RT-PCR) and amplified restriction fragment length polymorphism analysis, sloughed cells from the entire length of the colon and rectum were analyzed for expression of activating K-ras codon 12 mutants, which are becoming attractive targets for antisense treatment. K-ras codon 12 mutant sequences were detected in feces of 5% (1/20) of healthy controls, in feces of 41% (12/29) of CRC patients, in 10% (3/29) of isolates of tissue complementary DNA (cDNA), and in 14% (4/29) of isolates of genomic DNA. Age of patient was significantly associated with K-ras codon 12 sequences in feces: Patients with wild-type K-ras codon 12 sequences were significantly younger than those with mutated forms of K-ras codon 12. Fecal ribonucleic acid (RNA) analysis was demonstrated to be a useful for diagnosis of CRC. This technique may be suitable for screening and determining the clinical significance of active mutations of the K-ras gene in feces and would possibly be useful for identifying patients that would benefit from antisense therapy.

Determinants of colorectal cancer screening behavior among Chinese Americans

Colorectal cancer (CRC) is the most commonly diagnosed cancer among Chinese Americans and is the third leading cause of cancer death in this population. The objectives of this study were to determine the rates of CRC screening (via fecal occult blood test (FOBT), flexible sigmoidoscopy (FSIG), and colonoscopy) among Chinese Americans and predictors of utilizing these screening procedures. Participants (N = 206) completed a self-administered questionnaire assessing cancer screening behaviors and beliefs about perceived risk of developing cancer and treatment efficacy. A series of logistic regressions indicated that physician recommendation to obtain CRC screening significantly predicted whether Chinese Americans undergo FOBT, FSIG, or colonoscopy screening (p < 0.001). Acculturation and perceived risk of developing CRC did not predict obtaining any of the screening procedures. FOBT was the most commonly reported screening method used by respondents (65%), followed by FSIG (54%) and colonoscopy (49%). These findings highlight the need to make physicians more aware of the impact their recommendations have in determining CRC screening behavior among Chinese Americans.

Multiple primary malignancies in patients with renal cell carcinoma: a national population-based cohort study

OBJECTIVE

To determine the possibly greater occurrence of multiple malignancies in patients with renal cell carcinoma (RCC).

PATIENTS AND METHODS

In the 7-year period 1987-93, all 1425 patients aged 15-70 years with registered histopathologically verified RCC in Norway were included in the study. All clinical and histopathology reports were checked manually, to verify the registered diagnosis and to ensure that no tumour was a metastasis from another. After this process, 257 patients (287 tumours other than RCC) with multiple primary malignancies were identified. The primary tumours other than RCC were classified as antecedent, synchronous and subsequent. For the subsequently occurring tumours, the expected number of different tumour types was calculated according to age group, gender and observation time.

RESULTS

Of the 1425 patients, 228 (16%) had one, 23 (1.6%) had two, three (0.2%) had three and one (0.07%) had four other primary malignancies. In all, 100 (34.8%) of the other tumours were diagnosed as antecedent, 53 (18.7%) as synchronous and 134 (46.7%) as subsequent to the RCC. Cancer in the prostate, bladder, lung, breast, colon and rectal cancer, malignant melanomas (MM) and non-Hodgkin's lymphomas (NHL) were the most common other malignancies. The observed overall number of subsequent other malignant tumours was 22% higher than the expected number. The observed number of subsequent tumours was significantly higher for bladder cancer, NHL and MM. The estimated 15-year cumulative risk for patients with RCC and no previous or synchronous other malignancy for developing a later second cancer was 26.6% in men, and 15.5% in women (statistically significant, P = 0.04). Patients with antecedent or synchronous other cancer had significantly poorer overall survival than those without.

CONCLUSIONS

Patients with RCC seem to have a significantly higher risk of developing other subsequent primary malignancies. This should be considered during the follow-up of patients with RCC.

Analysis of Mortality Data From Cancer Screening Studies

BACKGROUND

Appropriate statistical analysis is required to measure the impact of early detection and treatment of cancer. The current practice of using cumulative mortality ignores both (1) the delay between early treatment and the time that any averted deaths would have otherwise occurred, and (2) cessation of these delayed benefits some time after screening is discontinued.

METHODS

We use time-specific mortality density ratios to estimate the mortality ratio in the "window of influence." We then use time-specific incidence density ratios to assess the extent to which the removal of polyps and other possibly precancerous lesions detected by fecal occult blood screening reduces the incidence of colorectal cancer.

RESULTS

Applied to a theoretical example, the current practice of using cumulative mortality substantially underestimates the reduction in mortality achievable by early treatment. If there is sufficient time for the full impact to emerge, time-specific mortality patterns provide a more accurate measure. In a previous analysis of the screening study, the reduction in cumulative incidence in the screened groups was just under 20%. In our reanalysis, yearly incidence density ratios indicate that had screening not been interrupted, there might have been a 40% reduction in incidence.

CONCLUSIONS

Time-specific mortality ratios provide a more sensitive measure of the effects of early detection and treatment. Measures based on cumulative mortality are diluted by inclusion of deaths that occur soon after the initiation of screening as well as deaths that occur too long after the cessation of screening.

Detection of K-ras gene mutation in fecal samples from elderly large intestinal cancer patients and its diagnostic significance

AIM: To study the diagnostic significance of K-ras gene mutations in fecal samples from elderly patients with large intestinal cancer.

METHODS: DNA was extracted in the fecal and tissue samples from 23 large intestinal cancer patients, 20 colonic adenomatoid polypus patients and 20 healthy subjects. The K-ras gene mutations at the first and second bases of codon 12 were detected by the allele specific mismatch method.

RESULTS: The K-ras gene mutation was 56.52% (13/23) in the large intestinal cancer patients, which was notably higher than that in the normal subjects whose K-ras gene mutation was 5% (1/20) (Χ² = 12.93, P < 0.001). There was no significant difference in comparison with that of colonic adenomatoid polypus patients whose K-ras gene mutation was 30% (6/12) (Χ² = 3.05, P > 0.05). The K-ras gene mutation at the second base of codon 12 was 92.13% (12/13) in the large intestinal cancer patients. There was no significant difference between the detection rate of K-ras gene mutation in the fecal and tissue samples (Χ² = 9.35, P < 0.01).

CONCLUSION: Our results indicate that detection of the K-ras gene mutations in fecal samples provides a non-invasive diagnostic method for the elderly large intestinal cancer patients. Its significance in the early diagnosis of large intestinal cancer awaits further studies.