The TP53 tumour suppressor gene in colorectal carcinomas. I. Genetic alterations on chromosome 17

Molecular biomarkers in colorectal carcinoma

Colorectal cancer is a tumor with increasing incidence which represents one of the first leading causes of death worldwide. Gene alterations described for colorectal cancer include genome instability (microsatellite and chromosomal instability), CpG islands methylator phenotype, microRNA, histone modification, protein biomarkers, gene mutations (RAS, BRAF, PI3K, TP53, PTEN) and polymorphisms (APC, CTNNB1, DCC). In this article, biomarkers with prognostic value commonly found in colorectal cancer will be reviewed.

Macroscopic morphologic subtypes of laterally spreading colorectal tumors showing distinct molecular alterations

Recent advances in colonoscopic techniques have resulted in more frequent detection of superficial-type colorectal tumors, that is, laterally spreading tumors (LSTs), although little is known about the characteristic clinical features and genetic alterations of LSTs. To elucidate the molecular characteristics of LSTs, genetic alterations in the KRAS, BRAF and PIK3CA genes and abnormal expression of the p53, beta-catenin and MYC proteins were analyzed using direct DNA sequencing and immunohistochemistry for 50 protruded-type tumors (Protruded), 35 granular-type LSTs (LST-G) and 19 nongranular-type LSTs (LST-NG). In addition, loss of heterozygosity (LOH) close to the adenomatous polyposis coli (APC) gene (5q21) was examined in these tumors. In univariate analyses, significant differences were noted in the percentages with KRAS mutations (Protruded, LST-G, LST-NG = 30.0%, 54.3%, 21.1%, respectively, p = 0.0156), nuclear accumulation of beta-catenin (Protruded, LST-G, LST-NG = 50.0%, 37.1%, 68.4%, respectively, p = 0.0267), expression of MYC (Protruded, LST-G, LST-NG = 26.0%, 17.1%, 42.1%, respectively, p = 0.0456) and LOH at the APC gene locus (Protruded, LST-G, LST-NG = 22.0%, 20.0%, 47.4%, respectively, p = 0.0302). Multivariate analysis demonstrated that the macroscopic subtype of LST was significantly associated with KRAS mutation (for LST-NG: odds ratio [OR] 0.23, 95% CI 0.06-0.90) and nuclear accumulation of beta-catenin (for LST-NG: OR 4.05, 95% CI 1.11-14.8). Our data revealed that the 2 subtypes of LST have different molecular characteristics, suggesting that 2 or more different molecular mechanisms result in colorectal tumors with a similar growth pattern.

Allele-specific loss of heterozygosity in multiple colorectal adenomas: toward an integrated molecular cytogenetic map II

Colorectal cancer (CRC) remains a significant public health challenge despite our increased understanding of the genetic defects underlying the pathogenesis of this common disease. It has been thought that multiple mechanisms lead to the malignant phenotype, with familial predisposition syndromes accounting for only a small proportion of all CRC cases. To identify additional loci likely involved in CRC and to test the hypothesis of allele-specific loss of heterozygosity (LOH) for the localization of CRC susceptibility genes, we initially conducted a genome-wide allelotyping analysis of 48 adenomas from a patient with familial adenomatous polyposis coli (FAP) and 63 adenomas from 7 patients with sporadic CRC using 79 fluorescently tagged oligonucleotide primers amplifying microsatellite loci covering the human genome. Frequent allelic losses were identified at D17S802 (41%), D7S518 (40%), D18S53 (38%), D10S249 (32%), D2S391 (29%), D16S419 (27%), D15S1005 and D15S120 (24%), D9S274 and D11S1318 (23%), D14S65 (20%), D14S274 and D17S953 (19%), D19S424 (18%), D5S346 and D1S397 (15%), and D6S468 (13%) in multiple FAP adenomas. Common LOH was also detected at D4S1584 (42%), D11S968 (31%), D17S953 (28%), D5S394, D9S286 and D10S249 (24%), D8S511 (23%), D13S158 (21%), D7S669 (20%), D18S58 (19%), D2S162 and D16S432 (16%), D2S206 (15%), D7S496 and D17S946 (14%), D6S292 (13%), D4S1586 and D8S283 (11%), and D1S2766 (10%) in multiple CRC adenomas. In addition, allele-specific LOH at D5S346, D15S1005, and D15S120 was observed in multiple FAP adenomas (P < 0.01) and at D2S206 and D16S423 in multiple CRC (P < 0.05). To compare our data to previous reports, we determined the band-specific frequency of chromosomal imbalances in CRC karyotypes reported in the Mitelman database, and from the CGH results of cases accessible through the PROGENETIX website. Furthermore, published genome-wide allelotyping analysis of CRC and other allele-specific LOH studies were compiled and collated with our LOH data. The combined results not only provide a comprehensive view of genetic losses in CRC, indicating the comparability of these different techniques, but they also reveal different novel loci in multiple adenomas from FAP and sporadic CRC patients, suggesting that they represent a distinct subtype of CRC in terms of allelic losses. Allele-specific LOH is an alternative approach for cancer gene mapping.

The TP53 colorectal cancer international collaborative study on the prognostic and predictive significance of p53 mutation: influence of tumor site, type of mutation, and adjuvant treatment

PURPOSE

The aims of the TP53 Colorectal Cancer (CRC) International Collaborative Study were to evaluate the possible associations between specific TP53 mutations and tumor site, and to evaluate the prognostic and predictive significance of these mutations in different site, stage, and treatment subgroups.

PATIENTS AND METHODS

A total of 3,583 CRC patients from 25 different research groups in 17 countries were recruited to the study. Patients were divided into three groups according to site of the primary tumor. TP53 mutational analyses spanned exons 4 to 8.

RESULTS

TP53 mutations were found in 34% of the proximal colon tumors and in 45% of the distal colon and rectal tumors. They were associated with lymphatic invasion in proximal tumors. In distal colon tumors, deletions causing loss of amino acids were associated with worse survival. In proximal colon tumors, mutations in exon 5 showed a trend toward statistical significance (P < .05) when overall survival was considered. Dukes' C tumors with wild-type TP53 and those with mutated TP53 (proximal tumors) showed significantly better prognosis when treated with adjuvant chemotherapy.

CONCLUSION

Analysis of TP53 mutations from a large cohort of CRC patients has identified tumor site, type of mutation, and adjuvant treatment as important factors in determining the prognostic significance of this genetic alteration.

Genetic tumor markers with prognostic impact in Dukes' stages B and C colorectal cancer patients

PURPOSE

To examine several genetic changes in primary colorectal carcinomas (CRCs) from patients with 10 years of follow-up and associate the findings with clinicopathologic variables.

MATERIAL AND METHODS

DNA from 220 CRCs were analyzed for allelic imbalances at 12 loci on chromosome arms 1p, 14q, 17p, 18q, and 20q, and the microsatellite instability (MSI) status was determined. The clinical significance of the tumor protein 53 (TP53) mutations was re-evaluated.

RESULTS

Patients with tumors containing 17p or 18q deletions had shorter survival than those without these alterations (P =.021, P =.008, respectively). This was also significant for the Dukes' B group (P =.025, P =.010, respectively). Furthermore, patients with tumors showing losses of both chromosome arms revealed an even poorer disease outcome than those with either 17p or 18q loss. Patients with low increase in 20q copy number in their tumors had longer survival compared with those without changes (P =.009) or those with a high increase of copy number (P =.037). This was also evident for the Dukes' C group (P =.018, P =.030, respectively). MSI was seemingly a beneficial marker for survival (P =.071). A significant association between mutations affecting the L3 zinc-binding domain of TP53 and survival was confirmed in this cohort after 10 years of follow-up, and also was found to apply for patients in the Dukes' B group. Several associations were found among genetic and pathologic data.

CONCLUSION

The present study indicates that 17p, 18q, and 20q genotypes, and TP53 mutation status add information in the subclassification of Dukes' B and C patients and may have impact on the choice of treatment.

The colorectal adenoma-carcinoma sequence

BACKGROUND

It is widely accepted that the adenoma-carcinoma sequence represents the process by which most, if not all, colorectal cancers arise. The evidence supporting this hypothesis has increased rapidly in recent years and the purpose of this article is to review this evidence critically and highlight its clinical significance.

METHODS

Medline searches were used to identify recent key articles relating to the adenoma-carcinoma sequence. Further pertinent articles were obtained by manual scanning of the reference lists of identified papers.

RESULTS

The evidence supporting the adenoma-carcinoma sequence can be classified as epidemiological, clinicopathological and genetic. The most recent and largest body of data relates to molecular genetic events and their cellular effects; however, many other approaches, such as cytogenetics, molecular cytogenetics and cytometry, have also yielded valuable information.

CONCLUSION

Recent work continues to support the adenoma-carcinoma sequence, but there is a paucity of data on the interrelationship between different genetic mutations and on the relationship between molecular and other types of genetic abnormalities. The clinical utility of the observations described has yet to be fully realized and global genetic analysis of colorectal tumours may prove to be central in rational adenoma management.

Use of crypt isolation to determine loss of heterozygosity of multiple tumor suppressor genes in colorectal carcinoma

Analysis of loss of heterozygosity (LOH) is very important in the study of tumor suppressor genes. However, accurate LOH analysis of tumor suppressor genes is difficult because of dilution by contaminating non-tumor DNA. Thus, enrichment of tumor DNA is required to accurately determine LOH of the tumor. We developed a new application of the fluorescent polymerase chain reaction by coupling it with crypt isolation to accurately assess the incidence of LOH of tumor suppressor genes in 45 colorectal carcinomas. LOH was observed at p53 in 26 of 37 tumors (70.3%), at APC in 13 of 35 (37.1%), at DCC in 16 of 25 (64.0%), at NF-2 in 5 of 23 (21.7%), and at nm23 H-1 in 7 of 30 (23.3%). We could clearly determine LOH of these genes because the crypt isolation technique was used. Although the incidence of LOH at each of these loci, as determined by using this technique, was similar to that obtained in previous studies using conventional methods, this method provides a simpler, more accurate way to assess LOH. In addition, the morphology of the samples can be analyzed before genetic analysis.

Association of p53 accumulation with TP53 mutations, loss of heterozygosity at 17p13, and DNA ploidy status in 273 colorectal carcinomas

The aim of this study was to establish an experimentally based cutoff level for assessing p53 immunoreactivity in colorectal tumors. The accumulation of p53 protein in 273 colorectal tumors was correlated with previously obtained data on TP53 mutation and loss of heterozygosity at two 17p13 loci in the same tumors. The monoclonal antibody PAb 1801 was used for p53 staining, and the results obtained by immunohistochemistry and immunoblotting were similar. Mutation analyses of exons 5-8 were performed using constant denaturant gel electrophoresis followed by sequencing. There were no statistically significant differences for any measured TP53 gene alteration between the group of tumors without p53-positive nuclei (n = 83) and the group with <5% positive nuclei (n = 58). The majority of mutations within these groups were deletions/insertions and nonsense mutations without p53 accumulation. Therefore, we assume that 5% p53-positive nuclei is the relevant cutoff level to assess TP53 damage in colorectal tumors. A prerequisite for this recommendation is optimal conditions for p53 protein detection. The parameters for p53 dysfunction were correlated to DNA aneuploidy measured by flow cytometry. TP53 mutations were significantly associated with DNA aneuploidy (P < 0.00001), and a nonrandom distribution of TP53 gene alterations among diploid (DI = 1), hyperdiploid (1.0 < DI < 1.3), and highly aneuploid (DI > 1.3) tumors indicates that DNA hyperdiploid tumors constitute a separate developmental entity different from tumors with gross aneuploidy.

Genetic alterations in colorectal cancer, comparative analysis of deletion events, and point mutations

Although data on genetic alterations leading to the development of colorectal cancer are abundant, no specific genetic alteration, as has been demonstrated for certain rare tumors such as lymphoma, leukemia, or sarcoma, has been shown to be responsible for the development of colorectal carcinomas. The colorectal cancer phenotype undoubtedly originates from an accumulation of different genetic alterations. The nature of these alterations, their order of appearance, and their associations vary greatly from one tumor to another, suggesting that the concept of a unique model of carcinogenesis is not applicable to these tumors. We studied a panel of 40 colorectal tumors in an attempt to identify different carcinoma subsets distinguishable by the pattern of genetic alterations. We examined a series of genetic anomalies frequently implicated in the development of colorectal cancer, including genetic material loss, demonstrated by loss of heterozygosity on chromosome arms 1p, 17p, and 18q; mutations of proto-oncogene K-RAS codons 12, 13, and 61; and gene TP53 mutations, identified by studying the accumulation of the corresponding immunohistochemically detectable protein. Our findings showed an important correlation between the genetic material loss events and an independent distribution of point mutations, which favors the hypothesis of a specific type of genetic instability characterized by the recurrent loss of chromatin fragments implicated in a subset of colorectal cancers.

Topographic genotyping of colorectal carcinoma: from a molecular carcinogenesis model to clinical relevance

BACKGROUND

In recent years, as a result of refinement in molecular biology techniques, significant progress has been made in the understanding of colorectal carcinogenesis. Particular attention has been drawn to identification of genetic mutation that may predispose to colorectal carcinoma (familial syndromes) and may affect tumor behavior and prognosis (sporadic cases).

CONCLUSIONS

Our method of topographic genotyping of human colonic carcinomas has shown a correlation between K-ras-2 and p53 mutations and stage at diagnosis as well as long-term survival. Data from other investigators in this field confirm the importance of genetic analysis of human colorectal tumors. These findings are likely to impact management by allowing a more individualized therapeutic approach.

Variations in c-erbB-2 proto-oncogene status in breast cancer tumors as detected by two different cDNA probes

We examined 232 breast carcinomas for c-erbB-2 amplification by Southern analysis using two different cDNA probes. Using these same probes, 95 of these tumors were also examined for mRNA expression by Northern analysis. Amplification was detected in 20 and 17% of the tumors with the probes pHER 2 and pCER 204, respectively, but only 10% showed amplification with both probes. A significantly higher incidence (p < 0.01) of mRNA overexpression was detected with the pHER 2 probe (34%) compared with the pCER 204 probe (16%), with only 11% of tumors demonstrating overexpression with both probes. A total of 10 tumors (11%) exhibited amplification as well as overexpression with pHER 2, whereas significantly fewer (3%) manifested both abnormalities with the larger pCER 204 probe (p < 0.05). Amplification of c-erbB-2, as detected with the pHER 2 probe but not with the pCER 204 probe, was significantly associated with the absence of both estrogen and progesterone receptors (p < 0.05 and p < 0.01, respectively). No relationship was found with other clinical prognostic indicators, such as nodal involvement and metastases. As determined by either probe, overexpression was not associated with prognostic indicators. There was no significant difference in the c-erbB-2 status of tumors from different racial groups.

Secretory component mRNA and protein expression in colorectal adenomas and carcinomas

Secretary component (SC) is expressed basolaterally as a transmembrane protein (pIg receptor) on secretory epithelial cells. As pIg receptor it plays a central role in humoral immunity by mediating the external translocation of dimeric IgA and pentameric IgM. A few case reports have suggested that reduced or absent SC protein expression is associated with diarrhoeal disease, but there is no convincing evidence that a primary pIg receptor deficiency can occur. In this study the relative presence of SC mRNA was determined by Northern blot analysis and related to immunohistochemically determined SC protein expression in 33 colorectal adenomas (31 patients) with increased risk of developing sporadic colorectal cancer, as well as in 19 colorectal carcinomas from 19 patients with such sporadic tumours. In the adenomas, SC mRNA levels were positively related to SC protein expression; both mRNA and SC protein were negatively related to histological grade. Similarly, SC mRNA levels tended to be related to the SC protein expression in the carcinomas. SC mRNA was detected in all adenomas, and only two of ten carcinomas (10.5%) deemed to be SC deficient by immunohistochemistry also lacked SC mRNA expression, suggesting diallelic alterations in the SC-encoding gene (locus PIGR). This possibility agreed with Southern blot analysis performed on a separate sample of 32 other colonic carcinomas in which the diallelic loss of D1S58 (which exhibits a close linkage centromerically to PIGR) was calculated to be 6.4%. Together these findings suggested that reduced SC protein expression in colorectal adenomas might be a transcriptional defect reflecting the degree of cellular dysplasia, whereas absent SC protein expression in colorectal carcinomas might also involve post-transcriptional defects and occasional diallelic gene deletions representing late events in carcinogenesis.

Prognostic value of TP53 and K-ras-2 mutational analysis in stage III carcinoma of the colon

BACKGROUND

Genetic mutations involving oncogenes and tumor-suppressor genes occur in carcinogenesis, and may affect biologic behavior of neoplasms. In this study, we analyzed the prognostic value of mutational analysis in colon carcinoma.

PATIENTS AND METHODS

Archival pathology specimens from 70 consecutive patients, resected for stage III colon carcinoma, were analyzed for point mutations by amplification and direct sequencing of exons from the K-ras-2 and the TP53 genes (topographic genotyping). Mutations were compared with adverse histopathologic features (poor differentiation, vascular and lymphatic invasion, mucin production) as prognostic markers.

RESULTS

Five-year survival was 75% in patients with nonmutated lesions, significantly lower (21%) with TP53 mutations (P = 0.01), and intermediate with K-ras-2 only (45%) or both K-ras-2 and TP53 mutations (36%). A TP53 mutation carried the highest relative risk of death (2.39; 95% confidence interval, 1.29 to 4.42; P = 0.006). There was an additive effect on the risk of death between TP53 mutations and adverse histopathologic features.

CONCLUSIONS

The information derived from mutational analysis is creating new prognostic variables that may play a role in the choice of therapy for colorectal carcinoma.

Antigen levels of urokinase plasminogen activator and its receptor at the tumor-host interface of colorectal adenocarcinomas are related to tumor aggressiveness

The distributions of urokinase and tissue plasminogen activators (uPA, tPA), uPA receptor (uPAR), and plasminogen activator inhibitors (PAI-1, PAI-2) were studied immunohistochemically in two subsets of colorectal adenocarcinomas with low and high aggressiveness, respectively: nine Dukes' stage A tumors with additional other good prognostic markers and 13 Duke's stage C tumors with also other poor prognostic markers (referred to as Dukes' stage A and Dukes' stage C tumors). The results showed that these components of the tissue destructive plasminogen activation system were accumulated at the invading front of the tumors. Both tumor groups showed accumulations of uPA, uPAR, and PAI-1 at the tumor-host interface compared with the location within the tumor epithelium and the adjacent normal mucosa and muscularis propria (all P < .05). However, the uPA level at the tumor-host interface in the Dukes' stage C tumors was twice the level in the Dukes' stage A tumors (P < .05). The uPAR level was also significantly higher in the Dukes' stage C tumors (P < .05), whereas the PAI-1 level was not significantly higher. This may indicate that uPA in more aggressive tumors exceeds the inhibitory capacity represented by PAIs, resulting in enhanced tissue destructive potential that promotes tumor invasion. uPA and uPAR antigen levels and the uPA/PAI-1 ratio at the tumor-host interface appeared to be related to tumor aggressiveness in colorectal cancer.

17q allele loss is associated with lymph node metastasis in locally aggressive human colorectal cancer

A consecutive series of 87 colorectal tumours were studied for loss of a polymorphic probe on chromosome 17q and of the 64 informative cases, 13 (20 per cent) showed loss of heterozygosity (LOH). Examples of LOH were found in carcinomas of all stages and in a large non-invasive adenoma. There was no correlation between 17q LOH and patient age, sex, standard clinicopathological variables (differentiation and nature of tumour margin), DNA ploidy, or tumour site, nor was 17q LOH associated with 17p LOH defined at four loci adjacent to p53. However, comparison of Dukes' B and C carcinomas revealed that tumours which had metastasized to regional lymph nodes at the time of primary surgery were significantly more likely to have lost this 17q allele. Clinical follow-up of this cohort of patients showed no significant difference in survival between patients whose tumours had lost or retained 17q. Thus, we conclude that 17q allele loss is associated with lymph node metastasis in locally aggressive colorectal tumours but probably not with blood-borne metastasis.

Frequency of allele loss of DCC, p53, RBI, WT1, NF1, NM23 and APC/MCC in colorectal cancer assayed by fluorescent multiplex polymerase chain reaction

We report here the use of multiplex fluorescent polymerase chain reaction (PCR) for quantitative allele loss detection using microsatellites with 2-5 base pair repeat motifs. Allele loss of APC, DCC, p53 and RB1 in colorectal tumours has been reported previously using a variety of methods. However, not all workers used intragenic markers. We have used microsatellite polymorphisms which map within, or are closely linked to, these tumour-suppressor gene loci in order to determine whether these loci are indeed the targets for alteration in colorectal cancer. In addition, we have assayed two other tumour-suppressor genes, WT1 and NF1, to see whether they play a role in colorectal carcinogenesis. The putative metastasis-suppressor gene, NM23, was also investigated since there have been conflicting reports about its involvement in colorectal carcinogenesis. Allele loss was detected at the DCC (29%), p53 (66%), RB1 (50%) and NF1 (14%) loci and in the APC/MCC region (50%), but not at the WT1 or NM23 loci. These rapid, and mostly gene-specific, fluorescent multiplex PCR assays for allele loss detection could be modified to devise a single molecular diagnostic test for the important lesions in colorectal cancer.

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.

Prognostic significance of the loss of heterozygosity of Nm23-H1 and p53 genes in human colorectal carcinomas

BACKGROUND

Nm23 is a gene associated with low tumor metastatic potential and has been proposed to be a metastasis suppressor gene. Nm23 is localized on chromosome 17q21.3-22, whereas the p53 suppressor gene is on 17p13. Allelic deletions of chromosome 17 have been related to the progression of colorectal carcinomas. The purpose of this study was to analyze the allelic deletions of Nm23 and p53 in colorectal carcinomas and to assess their prognostic significance in the evolution of the patients.

METHODS

Allelic deletions of Nm23 and p53 genes were studied in 56 colorectal carcinomas using different restriction fragment length polymorphisms. DNA ploidy and proliferative activity of the tumors were studied by flow cytometry. Actuarial disease free and overall survival were analyzed by the Kaplan--Meier method, and the curves were compared with the log rank test.

RESULTS

Thirty-eight patients were heterozygous for Nm23 gene (68%), and 9 of them (24%) exhibited a loss of heterozygosity in the tumor sample. One of the homozygous patients showed a loss of both Nm23 alleles. Allelic deletions of 17p13 were found in 63% of the 41 informative patients. All patients' tumors that had loss of heterozygosity of the Nm23-H1 locus also had allelic losses on the short arm of chromosome 17 (17p13) and in other loci on 17q. No relationship was found between localization, invasion, lymph node metastasis, or proliferative index of the tumors and the allelic deletions of the Nm23-H1 or 17p13 locus. Nm23-H1 deletions were relatively more frequent in poorly differentiated adenocarcinomas (P = 0.03). A significant association between 17p13 deletions and DNA aneuploidy was found (P = 0.016). A similar tendency was observed with Nm23-H1 deletions (P = 0.051). Loss of Nm23-H1, but not of 17p13, was significantly associated with a shorter disease free (P = 0.025) and overall (P = 0.04) patient survival.

CONCLUSIONS

Allelic deletions of Nm23-H1 are significantly associated with a more aggressive behavior of colorectal carcinomas. The loss of this gene seems to be part of extensive deletions of chromosome 17, and it is also associated with DNA aneuploidy. More studies are needed to determine whether Nm23-H1 or a gene linked to this locus is the specific target of the progression of these tumors.

K-ras mutation in colorectal cancer: relations to patient age, sex and tumour location

DNA from 251 primary tumours obtained from 123 male and 125 female Norwegian patients with colorectal carcinoma was analysed for the presence of K-ras point mutations at codons 12 and 13. Mutations were found in 99 (39%) of the samples. The frequency of K-ras mutations was significantly related to age and sex of the patients, and to the location of the tumours (overall: P = 0.008). K-ras mutations were much less frequent in colonic tumours from male than female patients at younger ages (< 40 years, odds ratio < 0.014). The low frequency might indicate that a different, ras-independent, pathway to neoplasia is dominating in the colon of younger males. In contrast, older men had more mutations than older women (e.g. 90 years, odds ratio = 5.8). An inverse but less pronounced relationship was seen for rectal tumours. The type of mutation was found to be associated to sex of patient and location of tumour. G-->C transversions accounted for 35% of the mutations in rectal tumours from females, in contrast to only 2.5% in the rest of the material (P = 0.0005). This may indicate that there are specific carcinogens acting in this location.

Familial and genetic aspects of colorectal carcinogenesis

There is abundant clinical and pathological evidence which suggests that colorectal cancer arises in a sequential manner through a series of events that can be followed during the progression of the disease from early adenoma through to metastatic disease. The molecular events that are associated with the initiation and progression of the disease are gradually being unravelled. As the molecular characterisation of colorectal cancer continues, new mechanisms by which the disease progresses are becoming evident. In this short review, a brief description of current knowledge of colorectal cancer development is presented.