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Query: UMLS:C0009402 (colorectal cancer)
 53,228 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Colorectal carcinogenesis is widely thought to follow the adenoma-adenocarcinoma sequence. However, there are two morphologically distinct subtypes of colorectal cancer (CRC), polypoid and ulcerative. We conducted a comparative study to clarify whether different combinations of some commonly involved genetic alterations (including mutations in K-ras, p53, DCC, APC, and Rb genes) may exist between polypoid- and ulcerative-type CRCs, the two morphologically distinct types of CRC. By using PCR-based RFLP, single-strand conformational polymorphism, and loss of heterozygosity analysis, we found that K-ras codon 12 mutation was preferentially involved in polypoid tumor (P < 0.0001). There were no other significant correlations with p53 point mutation or loss of heterozygosity in chromosomes 5q, 17p, and 18q and Rb gene, which have been suggested to be involved in the progression of CRC of both morphological types. Therefore, different combinations of molecular genetic alterations may be involved in morphologically distinct types of colorectal carcinogenesis, and the K-ras codon 12 mutations may play an important role in polypoid growth of CRC. These results shed light on the function of K-ras oncogenes involved in colorectal carcinogenesis and may be important in the future design of genetic screening programs, determination of prognosis, and treatment for patients with CRC.
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PMID:K-ras codon 12 mutation determines the polypoid growth of colorectral cancer. 969 57

Our purpose was to investigate different genetic abnormalities, such as K-ras mutations, p53 alterations, and c-myc RNA overexpression, as well as microsatellite instability in 63 colorectal tumors obtained from patients that had undergone surgery. K-ras point mutations were analyzed by PCR-RFLP technique, followed by sequencing; p53 protein accumulation by immunohistochemistry; p53 gene mutations in exons 5-9 were studied by the SSCP and sequencing techniques, and c-myc overexpression by Northern blot. Microsatellite instability was performed at chromosomes 2p, 3p, and 11p by a PCR-based technique. Our data indicate a trend toward a poorer prognosis in patients who had K-ras transversions; besides, we have obtained a prevalence of c-myc RNA overexpression and p53 exon 7 mutations in the latest stages of tumor progression. In conclusion, our findings suggest that the recognition of molecular abnormalities might be used in colorectal cancer as a prognostic indicator or to determine the metastatic potential of colorectal adenocarcinomas.
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PMID:Genetic abnormalities and microsatellite instability in colorectal cancer. 972 19

To study the appropriate period for formalin fixation in order to detect p53 abnormalities in formalin-fixed tissue, we used seven surgically resected human colorectal cancer specimens. The immunohistochemical reactivity of p53 immunostaining and amplification of DNA by polymerase chain reaction (PCR) of the p53 gene were compared after various periods of 10% formalin fixation (1 day, and 1, 2, 4, and 8 weeks). For comparative immunostaining, we used the monoclonal antibody Ki-67 (MIB-1), and for comparative polymerase chain reaction (PCR), K-ras at codon 12 was amplified. Immunostaining was performed by the streptavidin-biotin method with microwave retrieval, and PCR amplifications were performed by the nested PCR method. p53 and Ki-67 immunoreactivity did not change essentially for up to 2 weeks and 1 week, respectively, of formalin fixation. PCR amplification for p53 at exon 8 and K-ras at codon 12 was successful until 1 day and 2 weeks, respectively, of formalin-fixation for the specimens of all seven cases. Thereafter, the amplification tended to worsen as the fixation time lengthened. Further, the DNA was more successfully amplified in the second PCR than in the first. These results suggest that to detect p53 abnormality in specimens that have been formalin-fixed for long periods, immunohistochemical staining may have advantages over DNA analysis with PCR amplification.
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PMID:Advantages of immunostaining over DNA analysis using PCR amplification to detect p53 abnormality in long-term formalin-fixed tissues of human colorectal carcinomas. 977 51

A subset of hereditary and sporadic colorectal carcinomas is defined by microsatellite instability (MSI), but the spectra of gene mutations have not been characterized extensively. Thirty-nine hereditary nonpolyposis colorectal cancer syndrome carcinomas (HNPCCa) and 57 sporadic right-sided colonic carcinomas (SRSCCa) were evaluated. Of HNPCCa, 95% (37/39) were MSI-positive as contrasted with 31% (18/57) of SRSCCa (P < 0.000001), but instability tended to be more widespread in SRSCCa (P = 0.08). Absence of nuclear hMSH2 mismatch repair gene product by immunohistochemistry was associated with germline hMSH2 mutation (P = 0.0007). The prevalence of K-ras proto-oncogene mutations was similar in HNPCCa and SRSCCa (30% (11/37) and 30% (16/54)), but no HNPCCa from patients with germline hMSH2 mutation had codon 13 mutation (P = 0.02), and two other HNPCCa had multiple K-ras mutations attributable to subclones. 18q allelic deletion and p53 gene product overexpression were inversely related to MSI (P = 0.0004 and P = 0.0001, respectively). Frameshift mutation of the transforming growth factor beta type II receptor gene was frequent in all MSI-positive cancers (85%, 46/54), but mutation of the E2F-4 transcription factor gene was more common in HNPCCa of patients with germline hMSH2 mutation than in those with germline bMLH1 mutation (100% (8/8) versus 40% (2/5), P = 0.04), and mutation of the Bax proapoptotic gene was more frequent in HNPCCa than in MSI-positive SRSCCa (55% (17/31) versus 13% (2/15), P = 0.01). The most common combination of mutations occurred in only 23% (8/35) of evaluable MSI-positive cancers. Our findings suggest that the accumulation of specific genetic alterations in MSI-positive colorectal cancers is markedly heterogeneous, because the occurrence of some mutations (eg, ras, E2F-4, and Bax genes), but not others (eg, transforming growth factor beta type II receptor gene), depends on the underlying basis of the mismatch repair deficiency. This genetic heterogeneity may contribute to the heterogeneous clinical and pathological features of MSI-positive cancers.
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PMID:Accumulated clonal genetic alterations in familial and sporadic colorectal carcinomas with widespread instability in microsatellite sequences. 977 38

Microsatellite instability (MI) and K-ras oncogene mutation have been widely used as biomarkers of genetic changes in colorectal cancer (CRC). Each of these biomarkers was independently found in normal-appearing colonic mucosa at stages preceding the development of CRC, albeit at a relatively low incidence. To assess the potential value of combined MI and K-ras mutation analysis in the detection of normal-appearing colonic mucosa samples taken from patients with CRC, we have chosen to analyze multiple (3-7) normal colonic mucosa samples and the respective colorectal tumor tissues from 20 patients with CRC. As a control, we have used 54 normal mucosa samples obtained from 9 autopsies of patients without CRC. In at least 1 of 5 loci analyzed, MI was found in 8 of 20 patients via analysis of multiple normal-appearing colonic mucosa samples from each patient. Combined analysis of MI and mutant ras alleles in normal-appearing colonic mucosa samples enabled the identification of 11 of 20 patients with CRC. None of the 54 normal colonic mucosa samples obtained from 9 patients without CRC were found to carry mutant ras or MI. The ability to detect 55% of patients with CRC via the analysis of normal mucosa samples provides an important advance in our approach toward early detection of individuals who may be at risk to develop this tumor type.
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PMID:Combined analysis of microsatellite instability and K-ras mutation increases detection incidence of normal samples from colorectal cancer patients. 981 26

Point mutations in codons 12, 13, and 61 of the K-ras gene occur early in the development of colorectal cancer and are preserved throughout the course of tumor progression. These mutations can serve as biomarkers for shed or circulating tumor cells and may be useful for diagnosis of early, curable tumors and for staging of advanced cancers. We have developed a multiplex polymerase chain reaction/ligase detection reaction (PCR/LDR) method which identifies all 19 possible single-base mutations in K-ras codons 12, 13, and 61, with a sensitivity of 1 in 500 wild-type sequences. In a blinded study, 144 paraffin-embedded archival colon carcinomas were microdissected and K-ras mutations determined by both dideoxy-sequencing and multiplex PCR/LDR. Results were concordant for 134 samples. The ten discordant samples were re-evaluated using higher sensitivity uniplex PCR/LDR, and the original multiplex PCR/LDR result was confirmed in nine of these ten cases. Multiplex PCR/LDR was able to identify mutations in solid tumors or paraffin-embedded tissues containing a majority of wild-type stromal cells, with or without microdissection. The technique is well suited for large scale studies and for analysis of clinical samples containing a minority population of mutated cells.
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PMID:Multiplex PCR/LDR for detection of K-ras mutations in primary colon tumors. 992 17

Background: Topographic genotyping is a system of solid tissue molecular analysis designed to correlate microscopic alterations with specific forms of gene damage. In this system, microscopic targets are selected on the basis of cellular and immunohistochemical features. Minute tissue samples corresponding to these targets are precisely removed and analyzed for the presence and specific type of oncogene/tumor suppressor gene damage by means of polymerase chain reaction (PCR) followed by DNA sequencing. In this study, topographic genotyping was used to investigate the prognostic value of p53 and K-ras-2 mutational damage in 204 patients with colorectal cancer from two tertiary care centers. Methods and Results: The intensity and distribution of p53 immunohistochemical staining were correlated with the presence and specific type of mutational change, which resulted in a better understanding of the highly variable nature of p53 immunostaining patterns. Molecular genotype was correlated with the depth and extent of colorectal cancer spread (Dukes B and C) and with survival for follow-up periods of up to 10 years. An algorithm for p53/K-ras-2 genotyping was formulated to include p53 immunohistochemistry and DNA sequencing both of p53 exons 5-8 and of K-ras-2 exons 1 and 2. By using this algorithm, survival was shown to be significantly better in those patients whose tumors manifested normal p53 and K-ras-2 genes (P >.01). Patients with p53-mutated tumors composed a poor prognostic group, characterized by a high rate of intra-abdominal recurrence in the form of peritoneal seeding. Patients with K-ras-2-mutated tumors also composed a poor prognostic group, marked by a tendency for distant hematogenous metastasis involving lung, bone, and brain. Conclusions: Topographic genotyping's molecular diagnostic approach to colorectal cancer combines immunohistochemistry, PCR, and DNA sequencing. It is informative, cost-effective, timely, and yet fully integrated with standard histopathology. The use of this approach by pathologists as a model system for molecular diagnosis of colorectal cancer and other forms of solid tumor malignancy is recommended. As new prognostic molecular lesions are documented for tumor progression and metastasis, topographic genotyping will be well suited to facilitate their clinical application.
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PMID:Prediction of Biologic Aggressiveness in Colorectal Cancer by p53/K-ras-2 Topographic Genotyping. 1033 Jan 94

Epidemiological and experimental data suggest that dietary fiber and fat are major determinants of colorectal cancer. However, the mechanisms by which these dietary constituents alter the incidence of colon cancer have not been elucidated. Evidence indicates that dominant gain-of-function mutations short-circuit protooncogenes and contribute to the pathogenesis of cancer. Therefore, we began to dissect the mechanisms whereby dietary fat and fiber, fed during the initiation, promotion and progression stages of colon tumorigenesis, regulate ras p21 localization, expression and mutation frequency. Male Sprague-Dawley rats (140) were provided with corn oil or fish oil and pectin or cellulose plus or minus the carcinogen azoxymethane (AOM) in a 2 x 2 x 2 factorial design and killed after 34 weeks. We have previously shown adenocarcinoma incidence in these animals to be 70.3% (52/74) for corn oil + AOM and 56.1% (37/66) for fish oil + AOM (P < 0.05). Total ras expression as well as ras membrane:cytosol ratio was 4- to 6-fold higher in colon tumors than in mucosa from AOM- or saline-injected rats. Expression of ras in the mucosal membrane fraction was 13% higher for animals fed corn oil compared with fish oil feeding (P < 0.05), which is noteworthy since ras must be localized at the plasma membrane to function. The elevated ras membrane:cytosol ratio in tumors was not due to increased farnesyl protein transferase activity or prenylation state, as nearly all detectable ras was in the prenylated form. Phosphorylated p42 and p44 mitogen activated protein kinase (ERK) expression was two-fold higher in tumor extracts compared with uninvolved mucosa from AOM- and saline-injected rats (P < 0.05). The frequency of K-ras mutations was not significantly different between the various groups, but there was a trend toward a greater incidence of mutations in tumors from corn oil fed rats (85%) compared with fish oil fed rats (58%). Our results indicate that the carcinogen-induced changes in ras expression and membrane localization are associated with the in vivo activation of the ERK pathway. In addition, suppression of tumor development by dietary n-3 polyunsaturated fatty acids may be partly due to a combined effect on colonic ras expression, membrane localization, and mutation frequency.
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PMID:Carcinogen and dietary lipid regulate ras expression and localization in rat colon without affecting farnesylation kinetics. 1033 94

Colorectal cancer is a disease that is associated with default in the balance of apoptotic regulation. In the present study apoptosis was examined in 158 colorectal adenocarcinomas using the terminal deoxynucleotidyl transferase mediated digoxigenin nick end labeling (TUNEL) method. The median apoptotic index (AI) was 0.95% (range 0-6. 68%). Eighty-two tumours exhibited AI </=0.95% and 76 tumours showed AI >0.95%. We revealed a positive correlation between apoptosis and proliferation determined as the expression of proliferating cell nuclear antigen (PCNA, p=0.002). The frequency of apoptosis increased from Dukes' stage A, B, C to D (p=0.01). No correlations were found between apoptosis and the patients' sex, age, tumour location, growth pattern, differentiation, prognosis, bcl-2, p53 or K-ras. Our findings suggest that we should further investigate the relationship between apoptosis and cellular proliferative activity in colorectal cancer to evaluate whether this might provide additional information in the selection of patients for effective adjuvant therapy.
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PMID:Apoptosis in relation to proliferating cell nuclear antigen and Dukes' stage in colorectal adenocarcinoma. 1037 93

The majority of tumors from hereditary nonpolyposis colorectal cancer families and a subset of unselected gastrointestinal and endometrial tumors exhibit a microsatellite mutator phenotype (MMP) that leads to the accumulation of hundreds of thousands of clonal mutations in simple repeat sequences. The mutated genes with positive or negative roles in cell growth or survival in aneuploid gastrointestinal cancer (e.g., APC, K-ras, and p53) are less frequently mutated in near-diploid MMP gastrointestinal tumors. These tumors accumulate mutations in other genes, such as DNA mismatch repair hMSH3 and hMSH6, transforming growth factor-beta type II receptor, and BAX. All these genes carry, within their coding sequences, mononucleotide repeats that are preferred targets for the MMP. Endometrial carcinoma is the most common type of extracolonic neoplasia in the hereditary nonpolyposis colorectal cancer syndrome, but the spectrum of its target cancer genes is not well characterized. Here, we report that endometrial cancer of the MMP also accumulates mutations in genes that are typically mutated in gastrointestinal cancer of the mutator pathway, including BAX (55%), hMSH3 (28%), and hMSH6 (17%). We also report the detection of frameshift mutations in caspase-5, a member of the caspase family of proteases that has an (A)10 repeat within its coding region, in MMP tumors of the endometrium, colon, and stomach (28, 62, and 44%, respectively). We therefore suggest caspase-5 as a new target gene in the microsatellite mutator pathway for cancer.
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PMID:Frameshift mutations at mononucleotide repeats in caspase-5 and other target genes in endometrial and gastrointestinal cancer of the microsatellite mutator phenotype. 1038 66


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