Concerted nonsyntenic allelic loss in human colorectal carcinoma

Genetic Events Responsible for Colorectal Tumorigenesis: Achievements and Challenges

Colorectal carcinogenesis is a multistep process that is accompanied by accumulation of changes in proto-oncogenes and tumor-suppressor genes. APC/MCC, RAS, DCC, p53 mutations and/or allelic losses, hyperexpression of c-MYC and RB genes, as well as other genomic alterations appear at characteristic stages of tumor development and are observed in most neoplasms. However, consideration of each of these abnormalities leaves many unanswered questions. The striking data on recurrent amplification of the RB tumor-suppressor gene as well as suppressive activities of protein kinase C and activated RAS genes, at least in some colon carcinoma cell lines, suggest the unusual effects of some signalling pathways in colonic epithelial cells. The results obtained to date indicate that distinct sets of genetic changes may underlie the development of colorectal tumors.

Screening of hub genes and pathways in colorectal cancer with microarray technology

Here we intend to identify key genes and pathways in the pathogenesis of colorectal cancer (CRC) through analyzing microarray data with bioinformatic tools. The gene expression profile dataset GSE23878 was downloaded from Gene Expression Omnibus and differentially expressed genes (DEGs) were screened out using Student's t-test. GO function and KEGG pathway enrichment analyses were performed for these DEGs with the DAVID online tool. Interaction network was constructed among the over-represented pathways based on the protein-protein interactions within the pathways. Besides, the protein interaction information obtained from HPRD database were applied to constructed protein-protein interaction networks among the DEGs and hub genes and function module were screened out. A total of 2,296 DEGs were obtained and they were enriched in 34 pathways. An interaction network was constructed among 32 pathways, in which p53 signaling pathway acted as the hub pathway as it showed the highest node degree. The protein-protein interaction network comprised 1,481 interaction relationships among 332 genes which included 40 DEGs. Further analysis revealed that theses DEGs formed 7 function modules and many genes, such as PDGFRB, MET, FZD2, CCND1, PRKCB, ARHGEF6, JUP, WNT2, WNT5A and WNT11 were key genes in the networks. The DEGs and disturbed biological functions uncovered in present study may play important roles in the development of CRC and can contribute to the understanding on molecular mechanisms of CRC. Further these DEGs we obtained can be acted as potential biomarkers for diagnosis and therapy of CRC.

Microsatellite instability in colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is the third most common cancer in the world. In 75% CRC develops sporadically, in 25% hereditary or as a consequence of inflammatory bowel disease. CRC carcinogenesis develops over many years. The cause of CRC in 85% is chromosomal instability (CIN) and in 15% microsatellite instability (MSI-H), where hereditary nonpolyposis colorectal cancer (HNPCC) represents 10-20%. Microsatellite sequences (MS) are repeated sequences of short stretches of DNA all over the genome. Microsatellite stability (MSS) means MS are the same in each cell of an individual, whereas microsatellite instability (MSI-H) means MS differ in normal and cancer cells of an individual. The cause of MSI-H is a damaged mismatch repair mechanism (MMR), with the most important MMR proteins being MSH2, MLH1 and MSH6.

CONCLUSIONS

MSI-H seems to be an important prognostic factor in CRC and an important predictive factor of CRC chemotherapeutic treatment efficacy. Clinical trials conducted until now have shown contradictory findings in different chemotherapeutic settings, adjuvant and palliative; therefore MSI-H is going to be the object of the future research. The future of cancer treatment is in the individualized therapy based on molecular characteristics of the tumour, such as MSI-H in CRC.

Clinical significance of preoperative serum vascular endothelial growth factor, interleukin-6, and C-reactive protein level in colorectal cancer

Background

Angiogenesis is a multistep process in which many growth factors and cytokines have an essential role. Vascular endothelial growth factor (VEGF) is a potent angiogenic agent that acts as a specific mitogen for vascular endothelial cells through specific cell surface receptors. The interleukin-6 (IL-6) pathway is another mechanism linking angiogenesis to malignancy. C-reactive protein (CRP), a representative marker for inflammation, is known for its association with disease progression in many cancer types. The aim of this study was to determine preoperative serum levels of VEGF, IL-6, and CRP in colorectal carcinoma, and to correlate them with disease status and prognosis.

Methods

A 132 of 143 patients who underwent curative resection for colorectal cancer were enrolled in this study. 11 patients with resection margin positive were excluded. Factors considered in analysis of the relationship between VEGF, IL-6, and CRP and histological findings. Patient prognosis was investigated. Serum levels of VEGF and IL-6 were assessed using Enzyme-Linked Immuno-Sorbent Assay (ELISA), and CRP was measured using immunoturbidimetry.

Results

Median follow-up duration was 18.53 months (range 0.73-43.17 months) and median age of the patients was 62 years (range, 26-83 years). Mean and median levels of VEGF and CRP in colorectal cancer were significantly higher than in the normal control group; 608 vs. 334 pg/mL and 528 (range 122-3242) vs. 312 (range 16-1121) (p < 0.001); 1.05 mg/dL vs. 0.43 mg/dL and 0.22 (range 0.00-18.40) vs. 0.07 (range 0.02-6.94) (p = 0.002), respectively. However mean and median level of IL-6 in patients were not significantly higher than in control; 14.33 pg/mL vs. 5.65 pg/mL and 6.00 (range 1.02-139.17) vs. 5.30 (4.50-13.78) (p = 0.327). Although IL-6 and CRP levels were not correlated with other pathological findings, VEGF level was significantly correlated with tumor size (p = 0.012) and CEA (p = 0.038). When we established the cutoff value for VEGF (825 pg/mL), IL-6 (8.09 pg/mL), and CRP (0.51 mg/dL) by Receiver Operating Characteristic (ROC) curve, we noted that high VEGF levels tended to reduce overall survival (p = 0.053), but not significantly. However, IL-6 and CRP demonstrated no significance with regard to disease free survival (p = 0.531, p = 0.701, respectively) and overall survival (p = 0.563, p = 0.572, respectively). Multivariate analysis showed that VEGF (p = 0.032), CEA (p = 0.012), lymph node metastasis (p = 0.002), and TNM stage (p = 0.025) were independently associated with overall survival.

Conclusions

Preoperative serum VEGF and CRP level increased in colorectal cancer patients. High VEGF level has been proposed as a poor prognostic factor for overall survival in patients with colorectal cancer.

Mouse skin models for carcinogenic hazard identification: utilities and challenges

This report addresses 1) the predictability of mouse skin models for carcinogenic hazard identification, 2) the association between early changes in the skin and later tumorigenic responses, and 3) the relative sensitivity of three mouse models of skin tumorigenesis; i.e. the genetically-initiated Tg.AC and RasH2 lines and the SENCAR mouse model. All three mouse models responded similarly, with mild inflammation and epidermal hyperplasia, to several weeks of treatment with a topical agent. Based on our previous research experience, we hypothesized that inflammation, irritation, proliferation, and/or hyperplasia in the skin would precede and predict the appearance of tumors in these sensitive mouse skin models. Consistent with our hypothesis, the test agent caused a low but significant tumorigenic response in Tg.AC mice. We propose that inflammation, irritation, and hyperplasia are sensitive predictors of a later tumorigenic response in Tg.AC mice. Further studies are needed, however, to better determine the relative sensitivity of these 3 models to a wider variety of agents.

APC, signal transduction and genetic instability in colorectal cancer

Colorectal cancer arises through a gradual series of histological changes, each of which is accompanied by a specific genetic alteration. In general, an intestinal cell needs to comply with two essential requirements to develop into a cancer: it must acquire selective advantage to allow for the initial clonal expansion, and genetic instability to allow for multiple hits in other genes that are responsible for tumour progression and malignant transformation. Inactivation of APC--the gene responsible for most cases of colorectal cancer--might fulfil both requirements.

Development and initial characterization of several new inbred strains of SENCAR mice for studies of multistage skin carcinogenesis

The development and initial characterization of five new inbred strains of SENCAR mice are described in this paper. Ten randomly selected pairs of outbred SENCAR mice were mated and offspring from each separately maintained parental line were sib mated at each successive generation to result in inbred strains. Due to poor reproductive performance only five of the original 10 lines were bred to homogeneity. Initial characterization of the five remaining lines (referred to as SL2/sprd, SL5/sprd, SL7/sprd, SL8/sprd and SLl0/sprd) at F12 for their responsiveness to a two-stage carcinogenesis protocol (10 nmol 7,12-dimethylbenz[a]anthracene and 0.25 microg 12-O-tetradecanoylphorbol-13 acetate) revealed three groups of responders in terms of the number of papillomas per mouse: SL2/sprd and SL8/sprd > SL7/sprd and SL10/sprd >> SL5/sprd. The papilloma responses in SL2/sprd and SL8/sprd were very similar to SENCAR B/Pt compared at the same doses. Papillomas induced on SL2/sprd had the highest propensity to progress to squamous cell carcinomas, similar to that observed in outbred SENCAR and SENCAR B/Pt mice. More detailed comparison of the responsiveness of SL2/sprd and SL5/sprd at Fl5 showed that these two inbred strains differed in their sensitivity to TPA-induced epidermal hyperplasia and that the dose of TPA required to produce a tumor response in SL5/sprd in comparison with that in SL2/sprd was 4-20 times higher. Overall, the availability of the different inbred SENCAR strains will greatly aid mechanistic studies of multistage skin carcinogenesis as well as studies to understand the underlying genetic basis of resistance to tumor promotion and progression in this model system.

Relationship between chromosomal aberrations by fluorescence in situ hybridization and DNA ploidy by cytofluorometry in osteosarcoma

An analysis of the chromosomal aberrations and DNA ploidy in the interphase nuclei of seven human osteosacomas was preformed by double-target fluorescence in situ hybridization (FISH) and DNA cytofluorometry. The FISH study of the numerical aberrations in chromosomes 1 and 17 or the structural aberrations in chromosome arm 1p or 17p was carried out by using four locus specific DNA markers, with one pair consisting of 1q12 and 1p36 and the other pair consisting of the 17 cemtromere and 17p13.3. There was no significant differences in the percentage of deletions in chromosome 1 and 17 between osteosarcomas and normal tissues. However, all seven tumors studied had extra copies. Cells with more than three probe signals were regarded as having chromosome polysomy. The percentage of polysomy of chromosome 1 was 20.0-64.0%, and chromosome 17 was 28.0-60.0%. The DNA ploidy patterns of hyperdiploid cells showing a greater DNA content than diploid cells were obtained by DNA cytoflurometry. Five of the seven tumors were non-diploid, and the remaining two were diploid. The percentage of polysomy was correlated with the percentage of hyperdiploid cells in each tumor. Thus, these findings indicated that the DNA ploidy changes were closely correlated with aberrations in the chromosome copy number in osteosarcomas.

Aberrations of chromosomes 1 and 17 in six human osteosarcoma cell lines using double-target fluorescence in situ hybridization

Analysis of six human osteosarcoma cell lines was performed by using double-target fluorescence in situ hybridization (FISH). FISH was applied to interphase nuclei, not to metaphase chromosomes. In this study, numerical aberrations of chromosomes 1 and 17 or structural chromosomal aberrations of chromosome arm 1p or 17p, in which it has been suggested that there are one or more tumor suppressor genes in various malignant tumors, were examined with this technique. All six of the human osteosarcoma cell lines studied had extra copies of chromosomes 1 and 17. A high frequency of deletions (> 60%) in chromosome 1 was found in two cell lines and deletions of chromosome 17 were found in one cell line.

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.

Allelic loss on chromosome 18q as a prognostic marker in stage II colorectal cancer

BACKGROUND & AIMS

Loss of heterozygosity (LOH) on chromosome 18q is frequent in colorectal cancer (CRC) and has been associated with poor prognosis in stage II tumors. This study investigated the frequency of LOH in sporadic CRC and its effect on patient prognosis.

METHODS

One hundred forty-four patients were screened for LOH at 18q by polymerase chain reaction using three polymorphic microsatellite markers.

RESULTS

Nineteen patients were excluded because their tumors showed microsatellite instability in at least one marker. Of the remaining 125 patients, 121 were informative in at least one marker; 45% (54 of 121) showed 18q LOH. Five-year survival was 42% in those with 18q LOH and 73% in those without 18q LOH (P = 0.008). Multivariate analysis showed that tumor side (P = 0.0001) and 18q LOH (P = 0.01) were the only independent prognostic factors. Examining markers individually showed that only the lost of D18S474 had a significant influence on survival in patients with stage II CRC (P = 0.016).

CONCLUSIONS

18q LOH indicates an unfavorable outcome in patients with stage II CRC. Our results emphasize the importance of the 18q21.1 region, where several tumor-suppressor genes have been mapped. Microsatellite analysis may be useful in identifying high-risk patients who might benefit from adjuvant therapy.

Allelic imbalance and microsatellite instability of the DCC gene in colorectal cancer in patients under the age of 35 using fluorescent DNA technology

AIM

To assess allelic imbalance and microsatellite instability in the region of the "deleted in colorectal cancer" (DCC) gene on chromosome 18q using fluorescent DNA technology in colorectal cancer in patients under the age of 35.

METHODS

Thirty two cases of colorectal cancer in patients under the age of 35 and with no family history of colon cancer were retrieved. DNA was extracted by standard methods, polymerase chain reaction (PCR) was performed using Cy5 labelled primers to microsatellite markers (D18S21, D18S34, and D18S58) in the DCC gene. The results were analysed using software attached to an automated DNA sequencer.

RESULTS

The patients ranged in age from 17 to 35 years. Nineteen were women, all had left sided tumours (tumours distal to the splenic flexure). Twenty eight cases were either stage C or D (using the Astler Coller system). The informativity of the three markers were as follows: D18S21, 25 of 32 (78.1%); D18S34, 18 of 32 (56.25%); D18S58, 24 of 32 (75%). Allelic imbalance for the markers, after excluding homozygous and microsatellite instability cases, was: D18S21, 31.8%; D18S34, 11.7%; and D18S58, 0%. Nine cases showed allelic imbalance for both D18S21 and D18S34, yielding a combined allelic imbalance frequency of 39.1%. Ten cases showed microsatellite instability in at least one marker, with microsatellite instability seen most commonly for D18S58. Three cases showed microsatellite instability for all three markers.

CONCLUSIONS

Approximately 39% of cases showed allelic imbalance for D18S21 and D18S34 markers, while microsatellite instability was found in 31.25% of cases. This figure is higher than that encountered in sporadic colorectal cancer over the age of 50, suggesting a role for the DNA repair genes in the pathogenesis of these cancers occurring under the age of 35.

Alternative genetic pathways in colorectal carcinogenesis

The comparative typing of matched tumor and blood DNAs at dinucleotide repeat (microsatellite) loci has revealed in tumor DNA the presence of alleles that are not observed in normal DNA. The occurrence of these additional alleles is possibly due to replication errors (RERs). Although this observation has led to the recognition of a subtype of colorectal cancer with a high incidence of RERs (caused by a deficiency in DNA mismatch repair), a thorough analysis of the RER frequency in a consecutive series of colorectal cancers had not been reported. It is shown here that the extensive typing of 88 colorectal tumors reveals a bimodal distribution for the frequency of RER at microsatellite loci. Within the major mode (75 tumors, RER- subtype), the probability that a locus exhibited instability did not differ significantly among loci and tumors, being 0.02. The subsequent development of a statistical test for an operational discrimination between the RER- and RER+ subtypes indicated that the probability of misclassification did not exceed 0.001 in this series. The frequency of K-ras mutation was found to be equivalent in the two subtypes. However, in the RER+ tumors, the p53 gene mutation was less frequently detected, the adenomatous polyposis coli (APC) mutation was rare, and the biallelic inactivation of either of these genes was not observed. Furthermore, the concomitant occurrence of APC and tumor growth factor beta receptor type II gene alterations was found only once. These data suggest that the repertoires of genes that are frequently altered in RER+ and RER- tumors may be more different than previously thought.

Utilization of microsatellites for the analysis of genomic alterations in colorectal cancers in Brazil

Two different pathogenetic mechanisms are proposed for colorectal cancers. One, the so-called "classic pathway", is the most common and depends on multiple additive mutational events (germline and/or somatic) in tumor suppressor genes and oncogenes, frequently involving chromosomal deletions in key genomic regions. Methodologically this pathway is recognizable by the phenomenon of loss of heterozygosity. On the other hand, the "mutator pathway" depends on early mutational loss of the mismatch repair system (germline and/or somatic) leading to accelerated accumulation of gene mutations in critical target genes and progression to malignancy. Methodologically this second pathway is recognizable by the phenomenon of microsatellite instability. The distinction between these pathways seems to be more than academic since there is evidence that the tumors emerging from the mutator pathway have a better prognosis. We report here a very simple methodology based on a set of tri-, tetra- and pentanucleotide repeat microsatellites allowing the simultaneous study of microsatellite instability and loss of heterozygosity which could allocate 70% of the colorectal tumors to the classic or the mutator pathway. The ease of execution of the methodology makes it suitable for routine clinical typing.

Microallelotyping defines the sequence and tempo of allelic losses at tumour suppressor gene loci during colorectal cancer progression

Microallelotyping of many regions from individual colorectal tumours was used to determine the sequence and tempo of allelic loss on 5q, 17p and 18q during neoplastic progression. No allelic losses were found in normal tissues surrounding colorectal neoplasms, but losses occurred abruptly on 5q at the transition from normal colonic epithelium to the benign adenoma, and on 17p at the transition from adenoma to carcinoma, indicating an essential role for these losses in tumour progression. Allelic losses were uniform throughout extensively microdissected benign adenomas and carcinomas. However, substantial allelic heterogeneity was found in high-grade dysplasia, the transition lesion between adenoma and carcinoma. Thus, allelic losses on 5q and 17p are associated with abrupt waves of clonal neoplastic expansion, and high-grade dysplasia is characterized by a high degree of allelic heterogeneity.

DNA-repeat instability is associated with colorectal cancers presenting minimal chromosome rearrangements

The DNA-repeat [(CA)n] instability of colorectal cancer cells was studied relative to our previously defined classification based on chromosome alterations. Of the 23 tumors analyzed, 13 belonged to the "monosomic" type (MT) characterized by simultaneous loss of chromosome 18 and chromosome arm 17p, and many structural rearrangements, 7 to the "trisomic" type (TT) with many chromosome gains but few rearrangements, and 3 had a normal karyotype (NT). (CA)n repeat sequences were examined on chromosomes 2, 5, 11, 13, 18, and 20. We found sequence alterations in 12 tumors at 1 or several loci, 9 of which (1/13 MT, 5/7 TT, and 3/3 NT) exhibited a typical shift in allele size defined as microsatellite instability. Furthermore, a single alteration was observed for the MT tumor, whereas one NT tumor displayed instability on two and all the other tumors on three or more loci. These results suggest an inverse relationship between the occurrence of chromosome structural rearrangements and microsatellite instability, providing another argument for the subdivision of colorectal cancers into groups of distinct oncogenic pathways.

Comparative clinicopathological and immunohistochemical study of ras and p53 in flat and polypoid type colorectal tumours

Mutations in oncogenes and tumour suppressor genes may have an important oncogenic role. Although flat type tumours have been frequently detected in recent years, ras and p53 expressions have not been studied in these tumours. Using a monoclonal and polyclonal antibody to the ras p21 and p53 product, paraffin wax embedded sections of 98 colorectal tumours (43 cases of the flat type colorectal tumour and 55 cases of polypoid type tumour) were stained using the immunoperoxidase technique. Staining was evaluated by light microscopic examination. Positive staining rate of ras p21 for the flat type was 0%; for the polypoid type, it was 60% in cancer with submucosal invasion, 82% in adenoma with high grade dysplasia, and 0% in adenoma with low grade dysplasia. The positive staining rate of p53 for the flat type was 50% in submucosal cancer, 9% in adenoma with high grade dysplasia, and 0% in adenoma with low grade dysplasia. For the polypoid type, it was 40% in submucosal cancer, 12% in adenoma with high grade dysplasia, and 0% in adenoma with low grade dysplasia. The intermediate staining rate of p53 in the polypoid type was 20% in submucosal cancer and 41% in adenoma with high grade dysplasia. It was seen that p53 was commonly expressed in both flat and polypoid lesions, p21 was not expressed in flat lesions, whereas it was commonly expressed in polypoid neoplasms. In the flat type cancer, a genetic change different from that of the polypoid type cancer is suggested.

DCC gene alteration in human endometrial carcinomas

The present study was undertaken to define the gene(s) of importance on the long arm of chromosome 18 (chromosome 18q) in endometrial carcinomas. We analyzed loss of heterozygosity (LOH) at 3 loci on chromosome 18q and DCC gene expression by the reverse-transcriptase/polymerase chain reaction (RT-PCR) method. Among 61 tumors that were informative, 16 (26%), estimated to be a minimum number, showed allelic losses at one or more chromosome 18q loci. Deletions in these tumors possibly involved the region within or near the chromosome 18q 21.3 band where the DCC gene was localized. Moreover, the incidence of altered DCC mRNA expression was high in these tumors. Appropriate transcription was lost in 5 of 7 (71%) carcinoma cell lines in addition to 14 of 28 (50%) surgically resected tumors. Histopathological differentiation and clinical stage of disease were not related to LOH frequency or to DCC mRNA expression. These results suggest that the target for allelic loss on chromosome 18q seen in endometrial carcinomas is the DCC gene, and that inactivation of this gene may be critical for the development of most endometrial carcinomas.

Molecular genetics for clinical management of colorectal carcinoma. 17p, 18q, and 22q loss of heterozygosity and decreased DCC expression are correlated with the metastatic potential

BACKGROUND

The molecular genetic changes associated with colorectal carcinoma are among the best understood of any common human cancer. The genetic changes during the late stages of colorectal carcinomas may be useful in clinical management for determining the metastatic potential of the carcinoma.

METHODS

Tumor tissues were evaluated by restriction fragment length polymorphism (RFLP) analysis of chromosomes 5q, 17p, 18q, and 22q (n = 98), by reverse transcription-polymerase chain reaction (RT-PCR) analysis of messenger RNA expression of the DCC gene (deleted in colorectal carcinoma) (n = 27) and by immunohistochemical analysis of p53 protein expression (n = 44).

RESULTS

Loss of heterozygosity (LOH) on chromosomes 17p, 18q, and 22q, but not on 5q, was much more frequently detected in advanced carcinomas than in intramucosal carcinomas (P < 0.01). 17p LOH was significantly correlated with vascular invasion (P < 0.001), whereas 18q LOH was correlated with lymphatic invasion and hepatic metastasis (P < 0.01), and 22q LOH was correlated with lymph node metastasis (P < 0.05). LOH on 5q did not show a significant correlation with any factors of tumor invasion or metastasis. DCC expression was not observed in any of five hepatic metastasis or in five of seven advanced carcinomas that were accompanied by hepatic metastasis (10 of 12). However, a similar lack of expression was observed in only 5 of 15 carcinomas without hepatic metastasis (P < 0.05). p53 Expression was found to vary in both primary and metastatic carcinomas by immunohistochemistry.

CONCLUSIONS

The clinical application of molecular genetics (i.e., RFLP analysis of chromosome 17p, 18q, and 22q and RT-PCR analysis of DCC expression into messenger RNA) can be used to determine the metastatic potential of colorectal carcinomas.

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.

Putative dehydrogenase tms1 suppresses growth arrest induced by a p53 tumour mutant in fission yeast

Expression of a human tumour-derived p53 His 273 cDNA induced growth arrest in fission yeast Schizosaccharomyces pombe. Based on the p53-induced growth arrest, we cloned an extragenic suppressor, termed tms1, by complementation. The open reading frame of the tms1 gene corresponded to a protein of 347 amino acids with a calculated mass of 37380 Da. The transcriptional start site of the tms1 gene was mapped and, in addition, the corresponding cDNA was isolated and expressed in Escherichia coli. Recombinant tms1 protein served as an antigen to produce specific polyclonal antibodies to aid identification of the tms1-gene-product in total yeast lysates. Comparison of the deduced amino acid sequence of tms1 with available databases revealed significant similarity to dehydrogenases, suggesting that the tms1 protein itself might possess dehydrogenase activity.

Microsatellite instability in cancer of the proximal colon

Colorectal tumor DNA was examined for somatic instability at (CA)n repeats on human chromosomes 5q, 15q, 17p, and 18q. Differences between tumor and normal DNA were detected in 25 of the 90 (28 percent) tumors examined. This instability appeared as either a substantial change in repeat length (often heterogeneous in nature) or a minor change (typically two base pairs). Microsatellite instability was significantly correlated with the tumor's location in the proximal colon (P = 0.003), with increased patient survival (P = 0.02), and, inversely, with loss of heterozygosity for chromosomes 5q, 17p, and 18q. These data suggest that some colorectal cancers may arise through a mechanism that does not necessarily involve loss of heterozygosity.

Molecular genetic evidence for the delineation of a more severe form of familial adenomatous polyposis which results from fresh mutation

Familial adenomatous polyposis, an inherited pre-malignant condition, is caused by mutation in the adenomatous polyposis coli (APC) gene at chromosome 5q22. The lifetime risk of carcinoma approaches 100%, with an average age at death from cancer of 40 years, allowing most patients to complete reproduction. Since there is no evidence for a rising incidence, this is at variance with an apparently high mutation rate. We present evidence for the delineation of a severe form, which hitherto has largely been maintained by fresh mutation. An atypically high frequency of loss of heterozygosity at chromosome 5q22 in small adenomas correlated with an early age of onset or malignancy in two patients, both due to fresh mutation. In both cases, the mutation in APC was shown to be a commonly occurring deletion, leading us to postulate the co-existence of a modifying gene.

Genetics, natural history, tumor spectrum, and pathology of hereditary nonpolyposis colorectal cancer: an updated review

Hereditary nonpolyposis colorectal cancer (HNPCC) dates to Warthin's description of family G, which he began studying in 1895. Warthin's observations were not fully appreciated until 1966 when two families with an autosomal dominant inheritance pattern of nonpolyposis colorectal cancer (CRC) and endometrial cancer were described. This condition was first termed the "cancer family syndrome" and was later renamed HNPCC. Some have proposed that HNPCC consists of at least two syndromes: Lynch syndrome I, with hereditary predisposition for CRC having early (approximately 44 years) age of onset, a proclivity (70%) for the proximal colon, and an excess of synchronous and metachronous colonic cancers and Lynch syndrome II, featuring a similar colonic phenotype accompanied by a high risk for carcinoma of the endometrium. Transitional cell carcinoma of the ureter and renal pelvis and carcinomas of the stomach, small bowel, ovary, and pancreas also afflict some families. Current estimates indicate that HNPCC may account for as much as 6% of the total CRC burden. There are no known premonitory phenotypic signs or biomarkers of cancer susceptibility in the Lynch syndromes. This report will summarize current knowledge, with emphasis on the manner in which this knowledge can be employed effectively for diagnosis and management of HNPCC.

Chromosome analysis of adenomatous polyps of the colon: possible existence of two differently evolving cytogenetic groups

A chromosomal study of 42 colonic adenomatous polyps was performed using a technique of direct chromosome analysis derived from the prenatal procedure for diagnosing chromosomal alterations from chorionic villi sampling. Abnormal karyotypes were found in 22 cases. Trisomy 7, the most frequently found alteration, was found in 13 cases, followed by trisomy 13 (nine cases). Monosomy 18 was observed in two cases; in one of these, that of a polyp which had degenerated into an intra-mucosal adenocarcinoma, it was associated with 17p monosomy. Interestingly, these two types of alterations (trisomy 7 versus 18 and 17p monosomy) were not found together in the same lesion. This suggests that there could be two distinct chromosomal behaviors which might be related to the two cytogenetic groups described for colorectal adenocarcinoma. However, the respective frequencies of such cytogenetic groups varied inversely between adenomas and adenocarcinomas, thus suggesting that they evolve differently.

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.

Paraffin wax-embedded material as a source of DNA for the detection of somatic genetic changes

Loss of genetic material, corresponding to chromosomal deletions, has been detected in a wide range of tumours and may indicate the position of a tumour suppressor gene. In order to identify the position of such a gene more precisely, many tumour samples must be studied until a minimum consensus deletion is characterized. This process is particularly necessary for lung tumours in which the deletion in chromosome 3, seen with such high frequencies in all histological subtypes, is almost always large. We have recently described the use of the polymerase chain reaction (PCR) for restriction fragment length polymorphism (RFLP) analysis of DNA isolated from small bronchial biopsies of lung tumours. In this study we adapted this technique to allow genotyping of DNA isolated from paraffin wax-embedded material (PWEM) microdissected from glass slides. We have investigated 12 lung tumours at polymorphic loci on chromosome 3 and showed allelic loss in all samples. In adapting PCR-RFLP analysis for DNA isolated from PWEM, we have concentrated on those approaches which might be adaptable to routine clinical practice. Somatic genetic changes are now being identified in many tumour types, and this information is expected to be of diagnostic and prognostic significance.

Expression of oncogene products and growth factors in early gallbladder cancer, advanced gallbladder cancer, and chronic cholecystitis

The expression of oncogene products and growth factors (epidermal growth factor, transforming growth factor-beta, erbB-2, ras p 21, and c-myc) in gallbladder cancer and chronic cholecystitis was measured by immunohistochemical staining on paraffin-embedded serial sections. Expression of these products was graded according to staining intensity in an area of positively stained cells. This study reports the detection of oncogene products and growth factors in cholecystitis as well as in early and late gallbladder cancer. The multiexpression of oncogene products and growth factors was greater for both gallbladder cancer groups as compared with the cholecystitis group. The percentage of epidermal growth factor positivity diminished with increased proportion of interstitial tissue and, conversely, the percentage of transforming growth factor positivity increased with increased proportion of interstitial tissue. The proportion of ras positivity was significantly greater in both early and advanced cholecystic cancer as compared with cholecystitis, but also was considerable even for cholecystitis. These results suggest that various oncogenes may have significant roles in gallbladder cancer and that collagen synthesis is reduced by epidermal growth factor and enhanced by transforming growth factor-beta.

Increased p53 protein content of colorectal tumours correlates with poor survival

Allelic losses on the short arm of chromosome 17 occur frequently in colorectal cancers. Despite the existence of other common molecular events such as loss of the long arms of chromosomes 18 and 5, it has been demonstrated that the former has the greatest prognostic significance. Of the various genes mapping to the commonly deleted sequence, the best candidate as a 'target' seems to be the p53 antioncogene. We applied our methods of detection of the p53 protein in a series of 78 colorectal cancers stored in a tumour bank from 1985 to 1989, for which the median follow-up was 42 months. Nuclear-attached p53 was quantified by flow cytometry and soluble p53 was assayed by ELISA. Both assays used a monoclonal antibody considered to be specific for a conformational epitope present only on the mutated protein. Fifty of the 78 tumours (64%) were found to present significant levels of p53 attached to the nucleus. A further two tumours contained high levels of p53 only in their soluble fraction. Thus, 52 out of 78 cancers (67%) were considered to be positive for p53. The p53 content correlated with 17p loss (P < 0.002), hyperdiploid DNA content (P < 0.001) and tumour site (P < 0.03), but not Dukes' stage (P = 0.15). p53 negative cases had a better overall survival than p53 positive ones (P < 0.03). When the 14 stage D tumours were excluded from the analysis, p53 was no longer significantly predictive of survival (P < 0.07), but remained predictive of recurrence (P < 0.02) and metastasis (P < 0.03). Multivariate analysis was not performed because of the small number of cases. Overall, disease-free and metastasis-free survival were compared to the positivity obtained either with pAb 421 and/or 1801 or pAb 240 since all three were used in the flow cytometric analysis, defining subsets of 421-, 1801+ and 421-, 1801-, 240+. The presence of nuclear protein presenting the mutation-specific epitope, recognised by pAb 240, was found to be the most discriminant. It must be noted that univariate survival analysis demonstrated that more than 80% of patients with p53-negative tumours were alive at 3 years vs less than 50% in the p53-positive group. A large prospective study should be conducted to define the exact prognostic significance of the p53 content of colorectal carcinomas.

Current status of adjuvant chemotherapy for colorectal cancer. Can molecular markers play a role in predicting prognosis?

BACKGROUND

Recent clinical trials establish a beneficial effect for adjuvant chemotherapy after surgical resection of the primary tumor (1) as single treatment for patients with colonic cancer and (2) combined with radiation therapy for patients with rectal cancer. Because adjuvant chemotherapy is not universally effective and is associated with toxicity and some degree of risk, it would be desirable to supplement standard pathologic staging criteria to define more precisely the subset of patients at high risk for tumor recurrence who would benefit most from adjuvant therapy. Tumor cell DNA content and cell proliferation measured by flow cytometry were identified as important and independent prognostic factors for patients undergoing curative resection of colorectal cancer. Basic laboratory investigations show a series of more specific molecular and genetic abnormalities that might provide better prognostic discrimination. Recent molecular studies suggest that the process of tumorigenesis in colorectal cancer proceeds through a series of genetic alterations that include both dominant and recessive protooncogenes. Characterization of these molecular genetic abnormalities may provide valuable prognostic information for use in patient management.

METHODS

Allelic loss was studied for chromosomes 5, 17, and 18, and immunohistochemical analysis was done of the p53 protein product in tumors from 91 patients with colorectal cancer.

RESULTS

Preliminary analysis of disease-free survival after surgical resection in 60 patients with Dukes' B or C tumors suggests a poorer prognosis associated with allelic loss on chromosome 18q (P = 0.08).

CONCLUSIONS

Additional studies involving a much larger population of patients with Dukes' B and C colorectal cancer are needed to define the true prognostic significance of these molecular markers.

Colon cancer genetics

The terms "hereditary," "sporadic," and "familial" colorectal cancer (CRC) suggest a knowledge of causation; however, current understanding of CRC does not permit categorization of differing CRC risks in accord with their cause per se. Despite these serious shortcomings, these terms are defined operationally on the basis of a family history of cancer, and when available, additional phenotypic information. The sporadic type occurs in the absence of a family history of CRC in a first-degree relative. The familial type occurs when at least one first-degree relative has CRC. Both these categories require the exclusion of hereditary CRC. In the case of hereditary CRC, this type is defined as a family history of CRC occurring in a pattern that indicates autosomal-dominant inheritance, which also may involve certain phenotypic signs (depending on the specific disorder, i.e., florid adenomatous polyps, benign and malignant extracolonic lesions, cancer of unusually early onset, and multiple primary cancer, particularly synchronous and metachronous CRC). Although this operational classification does not produce etiologically homogeneous groups, it is believed to have pragmatic utility with respect to planning targeted surveillance and management strategies. Because of the distinctive natural history of CRC in hereditary syndromes, it is of paramount clinical importance to identify hereditary CRC when it does occur. Even in patients with no evidence of hereditary CRC syndrome, their family history may be second only to age in determining the best CRC screening program for those who are asymptomatic. In an attempt to provide a perspective on the clinical evaluation of CRC risk, research was reviewed on pathologic features and biomarkers that may be related to CRC causes, especially the genetic basis of CRC susceptibility. The long-term objective of studies on the genetic epidemiology of CRC is primary and secondary prevention through development of targeted management and surveillance recommendations (based on an understanding of CRC causation) that is relevant to hereditary, familial, and sporadic CRC.

Multiple intestinal neoplasia caused by a mutation in the murine homolog of the APC gene

Germ-line mutations of the APC gene are responsible for familial adenomatous polyposis (FAP), an autosomal dominantly inherited disease in humans. Patients with FAP develop multiple benign colorectal tumors. Recently, a mouse lineage that exhibits an autosomal dominantly inherited predisposition to multiple intestinal neoplasia (Min) was described. Linkage analysis showed that the murine homolog of the APC gene (mApc) was tightly linked to the Min locus. Sequence comparison of mApc between normal and Min-affected mice identified a nonsense mutation, which cosegregated with the Min phenotype. This mutation is analogous to those found in FAP kindreds and in sporadic colorectal cancers.

Gastrointestinal cancer: pathogenesis, risk factors and the development of intermediate biomarkers for chemoprevention studies

Dietary, environmental and genetic factors contribute to the etiology, pathogenesis and risk for gastrointestinal cancers. Measurements of cell proliferation and differentiation further identify abnormal cellular properties associated with increased susceptibility to gastrointestinal cancer. In precancerous esophagus, the proliferative compartment increases in size, increased ploidy and dysplasia develop, and epithelial cells express abnormal cytokeratins and ectopic tumor-associated antigens. In precancerous stomach, increased proliferative activity and metaplasia develop. Intestinal enzymes and mucins are expressed and normal gastric antigens are replaced by intestinal or embryonic antigens. In flat colonic mucosa and in colonic adenomas, expansions of the proliferative compartment occur. Gene expression is modified, gene deletions occur and blood group-related antigens are modified as the cells undergo abnormal differentiation and develop into adenomas and carcinomas. Chemopreventive regimens are now being tested to determine whether they modify such intermediate biomarkers toward normal levels characteristic of lower risk for neoplasia. It is anticipated that the utilization of intermediate biomarkers in chemoprevention studies may permit more novel chemopreventive regimens to be tested in human subjects than heretofore was possible.

Multistage carcinogenesis in mouse skin

The mouse skin model of multistage carcinogenesis has for many years provided a conceptual framework for studying carcinogenesis mechanisms and potential means for inhibiting specific stages of carcinogenesis. The process of skin carcinogenesis involves the stepwise accumulation of genetic change ultimately leading to malignancy. Initiation, the first step in multistage skin carcinogenesis involves carcinogen-induced genetic changes. A target gene identified for some skin tumor initiators is c-Ha-ras. The second step, the promotion stage, involves processes whereby initiated cells undergo selective clonal expansion to form visible premalignant lesions termed papillomas. The process of tumor promotion involves the production and maintenance of a specific and chronic hyperplasia characterized by a sustained cellular proliferation of epidermal cells. These changes are believed to result from epigenetic mechanisms such as activation of the cellular receptor, protein kinase C, by some classes of tumor promoters. The progression stage involves the conversion of papillomas to malignant tumors, squamous cell carcinomas. The accumulation of additional genetic changes in cells comprising papillomas has been correlated with tumor progression, including trisomies of chromosomes 6 and 7 and loss of heterozygosity. The current review focuses on the mechanisms involved in multistage skin carcinogenesis, a summary of known inhibitors of specific stages and their proposed mechanisms of action, and the relevance of this model system to human cancer.

Evidence for a common molecular pathogenesis in colorectal, gastric, and pancreatic cancer

We examined tissue extracted from 19 gastric, 7 pancreatic, and 23 colorectal carcinoma specimens to determine the comparative incidence of allele loss on chromosomes 5, 17, and 18 and that of KRAS2 point mutations. Chromosome 5 allele loss occurred at the same frequency in all three gastrointestinal tumors (approximately 30%), whereas chromosome 17 and 18 allele losses were seen at a significantly lower frequency in gastric (20%) and pancreatic (0%) malignancies than in colorectal cancer (57%). Point mutations in KRAS2 were seen in 83% of pancreatic and 52% of colon cancers, but not in gastric cancer specimens. In pancreatic tumors, these mutations were always found in the second nucleotide of codon 12. In colorectal cancer, the distribution was more variable, involving the second nucleotide of codon 13 and both the first and second nucleotides of codon 12. These results suggest that inactivation of the adenomatous polyposis coli gene on chromosome 5 may be an initiating step for carcinomas of the stomach and pancreas as well as of the colon, but that the genes involved in tumor progression events may be tissue- or tumor-specific.

Association of Ki-ras mutation with differentiation and tumor-formation pathways in colorectal carcinoma

The occurrence of a point mutation on the 12th and 13th codons of the Ki-ras oncogene has been investigated in 99 colorectal carcinomas in relation to 3 histological parameters: extent of differentiation, occurrence of a mucinous component within the tumor, and presence of peripheral adenomatous polyp remnants. The mutation frequency increased with each parameter: from 13% (2/15) to 44% (37/84) with differentiation, from 33% (26/79) to 65% (13/20) with mucinous character, and from 27% (15/56) to 56% (24/43) with the presence of polyp remnants. The frequency was highest in well-differentiated mucinous tumors with adenomatous remnants 83% (5/6). We suggest that Ki-ras mutation is preferentially involved in carcinomas that have developed from adenoma and that the mutation preserves differentiation and mucin secretion in these cancer cells.

Frequent loss of heterozygosity at the MCC locus on chromosome 5q21-22 in sporadic colorectal carcinomas

Recent studies have identified a gene on chromosome 5q, designated MCC (mutated in colorectal cancers), as a candidate for the putative colorectal tumor suppressor gene that is located at 5q21. We examined loss of heterozygosity (LOH) at the MCC locus and its vicinity in sporadic colorectal carcinomas, using 12 RFLP (restriction fragment length polymorphism) markers. One clone, L5.71, had been used to identify the MCC gene; all 12 markers also had tight linkage to the gene responsible for adenomatous polyposis coli. All 40 cases studied were informative with at least one marker, and 22 of them (55%) showed LOH at one or more loci. LOH in the tumors was more frequent in the immediate vicinity of L5.71 than in distant parts of the chromosome, and a common region of deletion was detected between markers L5.62 and 15A6. In one case, alleles were retained at L5.71 and at loci proximal to L5.71, but alleles were lost at loci distal to L5.71. In another case, both alleles were retained at L5.71 but alleles were lost at loci proximal and distal to L5.71. These results support the conclusion that a tumor suppressor gene for colorectal carcinoma is located within or around locus L5.71.

Identification of a germ-line mutation in the p53 gene in a patient with an intracranial ependymoma

We detected a germ-line mutation of the p53 gene in a patient with a malignant ependymoma of the posterior fossa. This mutation, which was found at codon 242, resulted in an amino acid substitution in a highly conserved site of exon 7 of the p53 gene; the same mutation was found in both the germ-line and the tumor tissue. This is the most common region of previously described somatic p53 mutations in tumor specimens and of the germ-line p53 mutations in patients with the Li-Fraumeni cancer syndrome. Evaluation of the patient's family revealed several direct maternal and paternal relatives who had died at a young age from different types of cancer. The association of a germ-line p53 mutation with an intracranial malignancy and a strong family history of cancer suggests that p53 gene mutations predispose a person to malignancy and, like retinoblastoma mutations, may be inherited.

Genetic alterations within the retinoblastoma locus in colorectal carcinomas. Relation to DNA ploidy pattern studied by flow cytometric analysis

Alterations within the retinoblastoma (Rb) gene, as detected by the VNTR probe p68RS2.0, and flow cytometric DNA pattern have been analysed in 255 colorectal carcinomas. A total of 35.3% of the tumours had alterations within the Rb gene. Amplification of one allele was demonstrated in 29.5% of the tumours, and loss of heterozygosity was found in 11.5%. No association was found between amplification within the Rb gene and clinicopathological characteristics of the patients. The high frequency of alterations demonstrated within the Rb gene, suggests that this gene is involved in colorectal carcinogenesis with amplification as by far the most abundant genetic alteration. This may imply that the Rb gene has an oncogene-like function in colorectal carcinomas, rather than acting as a tumour suppressor gene. Sixty-three per cent of the carcinomas were DNA aneuploid, and a significant association was demonstrated between amplification within the Rb gene and DNA aneuploidy (P less than 0.01). Two other chromosome loci were analysed, on chromosome 1p (probe pYNZ2) and on chromosome 2p (probe pYNH24), respectively. On chromosome 1p, heterozygous loss was found in 22.2% of the tumours, indicating an involvement of this chromosome in a subset of colorectal carcinomas.

Chromosome changes in desmoid tumors developed in patients with familial adenomatous polyposis

Chromosome analyses were performed on benign desmoid tumors obtained from two female patients with familial adenomatous polyposis (FAP), one of whom was diagnosed as having Gardner syndrome (GS). The modal chromosome number was 46 in both specimens, and detailed Q-banding analysis in Case 1 (GS) revealed a clonal abnormality of an interstitial deletion of the long arm of chromosome 5, del(5)(q21q31). The deleted region included an assigned locus for an FAP major gene (5q21-q22). All of the metaphases analyzed in this case showed an extra segment of bright fluorescence on the short arm of chromosome 15, but this unusual chromosome (15p+) was observed in both peripheral lymphocyte and skin fibroblast cultures from the patient, indicating that the 15p+ was constitutional in nature. In Case 2, no clonal rearrangements were identified and most cells had a normal karyotype. However, two cells showed rearrangements involving a 17q with non-identical breakpoints, one of which was observed as a solitary chromosome change. Based on the present findings in Case 1 and those reported so far, the chromosomal defect on 5q might be one of the causal genetic events primarily associated with the development of both benign desmoid tumors and colorectal adenomas and carcinomas in FAP patients.

Loss of allelic heterozygosity on distal chromosome 1p in Merkel cell carcinoma. A marker of neural crest origins?

The location of genes involved in tumor evolution has been inferred from experiments in which loss of constitutional heterozygosity has been detected in tumor DNA at high frequency in specific chromosome regions. For example, cytogenetic and molecular abnormalities on chromosome 1p have been reported in tumors such as malignant melanoma and neuroblastoma which arise in cells derived from embryonic neural crest tissue. To extend these observations, we have examined tumor DNA from three cases of Merkel cell carcinoma for evidence of loss of constitutional heterozygosity on the short arm of chromosome 1. In all three cases, heterozygous allelic deletions of varying extent on distal chromosome 1p were detected in tumor DNA. Comparisons with neural crest tumors suggest that loss of heterozygosity on distal chromosome 1p in Merkel cell tumors may be a marker of neural crest origin.

Hereditary nonpolyposis colorectal cancer (Lynch syndromes I & II). Genetics, pathology, natural history, and cancer control, Part I

Hereditary nonpolyposis colorectal cancer (HNPCC) is common, accounting for about 4-6% of the total colorectal cancer burden. It is heterogeneous and appears to be delineated into two clinical subsets, Lynch syndromes I and II. Lynch syndrome I is characterized by an autosomal dominantly inherited proclivity to early onset colonic cancer with proximal predominance and an excess of multiple primary colonic cancer. Lynch syndrome II has all of these features plus extracolonic cancer sites, the most common of which is endometrial carcinoma. The lack of premonitory physical signs or biomarkers of HNPCC makes diagnosis difficult. A careful family history, tempered by an understanding of the clinical and pathologic features of HNPCC, is the key to its assessment. This paper reviews HNPCC's natural history, its integral extracolonic cancer associations, its differential diagnosis, surveillance, and management strategies. Attention is focused upon the need for biomarker research in the interest of improving control of HNPCC.

Patterns of gene expression that characterize the colonic mucosa in patients at genetic risk for colonic cancer

We have used a computer-driven scanning and image-processing system to identify a panel of 30 cDNA clones whose pattern of expression in individual biopsy specimens distinguishes the flat, normal-appearing colonic mucosa of patients in two genetic groups at high risk for development of colorectal cancer from that of normal colonic mucosa in low-risk individuals. The two high-risk groups, familial adenomatous polyposis and hereditary nonpolyposis colon cancer, are indistinguishable based on the pattern of expression of the 30 selected clones. This suggests that the extensive pleiotropic effects of the inherited loci, which may play an important role in the mechanism of increased risk and early onset of the disease, are similar in these populations.

Suppression of tumorigenicity in human colon carcinoma cells by introduction of normal chromosome 5 or 18

Development of colon carcinomas can be associated with allelic deletions on several chromosomes, including 5q and 18q. The APC gene on 5q and the DCC gene on 18q have been identified as potential tumour suppressor genes, whose suppression contributes to colon carcinogenesis. To investigate the role of genes in these deleted regions, we have now introduced a single normal human chromosome into a human colon carcinoma cell line, COKFu, through microcell hybridization. Several clones of hybrid cells containing normal chromosome 5, and others containing normal chromosome 18, were obtained. The morphology of the hybrid cells was markedly altered: the hybrids with chromosome 5 exhibited a closely packed polygonal morphology, and the hybrid cells with chromosome 18 were flattened. The cloning efficiency of the hybrid cells in soft agar was reduced from 0.46 to 0% of that of the parental carcinoma cells, and the tumorigenicity of these hybrid cells in athymic nude mice was completely suppressed. The growth properties of the hybrid cells with chromosome 11 were not substantially changed. These results strongly suggest that the genes on normal chromosome 5 and 18 function as tumour suppressors in colon carcinogenesis.

Metabolic phenotypes and colorectal neoplasia

It now appears likely that the development of colonic adenomas and carcinomas involves a series of steps in which environmental or endogenous carcinogens induce or promote neoplasia through the accumulation of multiple, specific genetic mutations. Genetic predisposition to this process may take the form of inherited defects in control of cellular proliferation as in familial polyposis coli, or genetically determined polymorphism which affects enzyme activities relevant to the production or detoxication of carcinogens. Genetic effects may also influence levels of hormones and/or their target cell receptors which regulate the metabolic and proliferative activity of colonocytes. This review highlights data suggesting a role for polymorphism associated with xenobiotic acetylation, hydroxylation, and conjugation with glutathione in the metabolism of potential carcinogens, as well as for dehydroepiandrosterone in the metabolic control of cell proliferation. The study of genetically determined polymorphism in colorectal cancer may provide new insights into the epidemiology of cancer and result in new methods for the detection of higher risk groups.