Clinical and pathological associations with allelic loss in colorectal carcinoma [corrected]

Heredity, molecular genetics and colorectal cancer: a review

It is estimated that the hereditary polyposis and non-polyposis colorectal cancer (CRC) syndromes, which have an autosomal dominant pattern of inheritance, represent less than 10% of the total CRC burden. Thus, more than 90% of all cases of CRC have previously been considered to arise 'sporadically', with no identifiable genetic link. However, recent clinical evidence now suggests that a significant proportion of CRC seen in the general population may involve an inherited genetic susceptibility. Therefore, constructing an accurate family tree on all patients with a family history of CRC is an essential part of identifying families with an increased risk for CRC who could then be offered screening. Also, molecular genetic study of colorectal adenomas and carcinomas has led to a proposed genetic model of colorectal tumorigenesis which involves interactions between oncogenes and tumour suppressor genes. This information has important potential implications for screening, determining prognosis and for providing multiple targets for altering the sequence of malignant transformation.

Prognostic significance of cytoplasmic p53 oncoprotein in colorectal adenocarcinoma

Mutation of p53, a tumour-suppressor protein, leads to overexpression of the protein and loss of its tumour-suppressive properties. In some tumours (eg, breast) p53 expression is related to well-known prognostic factors, but findings in colorectal tumours are equivocal. We have used the polyclonal antibody CM1 to investigate nuclear and cytoplasmic p53 expression in colorectal tumours and to assess their relations with prognosis. Of 293 colorectal adenocarcinomas, 71 (24%) showed p53 expression in the nucleus alone, 30 (10%) showed p53 in the cytoplasm alone, and 43 (15%) showed both nuclear and cytoplasmic expression. Nuclear p53 expression showed no relation with survival or Dukes' stage of the tumour. However, the frequency of cytoplasmic expression increased with advancing Dukes' stage (chi 2 for trend 11.18, 1 df, p = 0.0008) and cytoplasmic expression was associated with poor survival (rate ratio 2.3 [95% CI 1.6-3.3], p < 0.0001). Among tumours of Dukes' stage A-C, cytoplasmic expression showed prognostic value independent of nuclear staining, grade of differentiation, and Dukes' stage (2.3 [1.4-3.7], p = 0.0021). We conclude that cytoplasmic expression of p53 may be a useful biological indicator of prognosis in colorectal adenocarcinoma.

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.

A 2-cM genetic linkage map of human chromosome 7p that includes 47 loci

A new high-resolution genetic linkage map for human chromosome 7p has been constructed. The map is composed of 47 loci (54 polymorphic systems), 19 of which are uniquely placed with odds of at least 1000:1. Four genes are represented, including glucokinase (GCK, ATP:D-hexose-6-phosphotransferase, EC 2.7.1.2) which was mapped via a (CA)n dinucleotide repeat polymorphism. The sex-average map measures 94.4 cM and the male and female maps measure 73.2 and 116.1 cM, respectively. We believe that the genetic map extends nearly the full length of the short arm of chromosome 7 since a centromere marker has been incorporated, and the most distal marker, D7S21, has been cytogenetically localized by in situ hybridization to 7p22-pter. The average marker spacing is 2 cM, and the largest interval between uniquely placed markers is 13 cM (sex-average map). Overall, female recombination was observed to be about 1.5 times that of males, and a statistically significant sex-specific recombination frequency was found for a single interval. The map is based on genotypic data gathered from 40 CEPH reference pedigrees and was constructed using the CRI-MAP program package. The map presented here represents a combined and substantially expanded dataset compared to previously published chromosome 7 maps, and it will serve as a "baseline" genetic map that should prove useful for future efforts to develop a 1-cM map and for construction of a contiguous clone-based physical map for this chromosome.

Overexpression of the p53 protein and allele loss at 17p13 in ovarian carcinoma

Mouse monoclonal antibodies PAb 240 and PAb 1801 which specifically immunoprecipitate p53 protein, were used to examine 27 fresh ovarian tumours (16 serous adenocarcinomas, six endometrioid carcinomas, one mucinous adenocarcinoma, one mucinous borderline tumour and three benign adenomas). Eleven out of 16 (69%) serous adenocarcinomas and one endometrioid tumour showed positive staining with one or both antibodies and none of the mucinous or benign tumours stained with either antibody. DNA from tumour and peripheral blood leukocytes was used to identify allelic deletions on chromosome 17p in tumours. 11/12 positively staining tumours showed less of heterozygosity (LOH) on 17p at the nearest informative locus to the p53 gene. In this series of ovarian tumours, LOH on 17p correlates closely with the aberrant expression of the p53 protein in a high proportion of advanced stage serous adenocarcinomas. This observation suggests that the p53 tumour suppressor gene is involved in the evolution of epithelial ovarian cancer (EOC) and may have prognostic significance.

MUC-2 human small intestinal mucin gene structure. Repeated arrays and polymorphism

MUC-2, the first described intestinal mucin gene, has become important as a prototype for secreted mucins in several organ systems. However, little is known about its protein backbone structure and hence its role in diseases such as colon cancer, ulcerative colitis, and cystic fibrosis, which are known to have mucin abnormalities. Studies in this manuscript show that MUC-2 contains two distinct regions with a high degree of internal homology, but the two regions bear no significant homology to each other. Region 1 consists mostly of 48-bp repeats which are interrupted in places by 21-24-bp segments. Several of these interrupting sequences show similarity to each other, creating larger composite repeat units. Region 1 has no length polymorphisms. Region 2 is composed of 69-bp tandem repeats arranged in an uninterrupted array of up to 115 individual units. Southern analysis of genomic DNA samples using TaqI and HinfI reveals both length and sequence polymorphisms which occur within region 2. The sequence polymorphisms have different ethnic distributions, while the length polymorphisms are due to variable numbers of tandem repeats.

Chromosomal localization of two human zinc finger protein genes, ZNF24 (KOX17) and ZNF29 (KOX26), to 18q12 and 17p13-p12, respectively

Two members of the zinc finger Krüppel family, ZNF24 (KOX17) and ZNF29 (KOX26), have been localized by somatic cell hybrid analysis and in situ chromosomal hybridization to human chromosomes 18q12 and 17p13-p12, respectively. The mapping of ZNF29 together with the previously reported localization of ZFP3 suggests that a zinc finger gene complex is located on human chromosome 17p. ZNF29 maps centromeric to the human p53 tumor antigen gene (TP53). In the analogous murine position, the two mouse zinc finger genes Zfp2 and Zfp3 have recently been assigned to the distal region of mouse chromosome 11, the murine homolog of human chromosome 17. Both human zinc finger genes ZNF24 and ZNF29 are in chromosomal regions that have been noted to be deleted in neoplasms of the lung and of the central nervous system at chromosome 17p and in colorectal neoplasia at chromosomes 17p and 18q.

Clinical research databases--a historical review

The increasing importance of computer-stored databases for clinical research prompted a historical review of their evolution over the past three decades. The special problems associated with the computer processing of clinical research data were reviewed, and the various types of clinical research registers and databases were described.

Allelic loss of chromosomes 16q and 10q in human prostate cancer

Recent advances in understanding the molecular genetics of common adult tumors have indicated that multiple genetic alterations including the activation of oncogenes and the inactivation of tumor suppressor genes are important in the pathogenesis of these tumors. Loss of heterozygosity is a hallmark of tumor suppressor gene inactivation and has been used to identify chromosomal regions that contain these genes. We have examined allelic loss in the most common tumor in men, prostate cancer. Twenty-eight prostate cancer specimens have been examined for loss of heterozygosity at 11 different chromosomal arms including 3p, 7q, 9q, 10p, 10q, 11p, 13q, 16p, 16q, 17p, and 18q. Fifty-four percent (13/24) of clinically localized tumors and 4 of 4 metastatic tumors showed loss of heterozygosity on at least one chromosome. Chromosomes 16q and 10q exhibited the highest frequency of loss of heterozygosity with 30% of tumors showing loss at these chromosomes. These data demonstrate that allelic loss is a common event in prostate cancer and suggest that chromosomes 16q and 10q may contain the sites of tumor suppressor genes important in the pathogenesis of human prostate cancer.

Comparison of deoxyribonucleic acid ploidy and nuclear expressed p62 c-myc oncogene in the prognosis of colorectal cancer

A simultaneous flow cytometric assay of the nuclear expressed protein product of the c-myc oncogene p62 and deoxyribonucleic acid (DNA) ploidy in archival paraffin-embedded tumor material was undertaken in 179 patients with colorectal cancer, followed for up to 9 years. DNA ploidy showed a survival advantage for diploid tumors (chi 2(1) = 5.39, p = 0.020) and could be used to further divide patients with Dukes' A tumors (chi 2(1) = 4.87, p = 0.027) and Dukes' C tumors (chi 2(1) = 5.33, p = 0.021). By dividing patients into 2 levels of tumor expression of p62 c-myc, there was a trend for improved survival in patients with low expression (chi 2(1) = 3.65, p = 0.056). A combination of ploidy status and p62 c-myc expression improved upon survival prediction by ploidy alone in providing 3 groups (chi 2(2) = 7.86, p = 0.0197). While these results do not suggest a replacement for the Dukes' staging for prognosis (chi 2(3) = 33.82, p less than 0.00001), they strongly support the concept that enhanced expression of c-myc oncogene is associated with the progression of colorectal cancer.

Familial cancer syndromes and clusters

Familial aggregation has been reported for virtually every form of cancer in humans. In general, close relatives of a cancer patient appear to have a twofold to threefold increase in risk for that tumor. Among cancer families, however, the level of excess risk is heterogeneous and ranges up to 1000-fold. Familial clusters of cancer are often due to inherited susceptibility, but environmental influences and chance association also must be considered. The effect of chance is large, due to the 50% lifetime risk of developing cancer that is present in the general U.S. population. Thus, a family history of cancer is the rule rather than the exception, and special studies are needed to distinguish predisposition from chance. An inherited susceptibility to cancer often becomes apparent through the occurrence of the same neoplasm among multiple blood relatives. These neoplasms tend to occur at earlier ages than usual, to appear bilaterally in paired organs, and to develop in multiple primary foci within the predisposed organ. Hereditary cancers can also develop as multiple primary tumors in organs that share the same embryological origins, as in the multiple endocrine neoplasia (MEN) syndromes. In addition, neoplasia occurs as a feature of diverse inherited diseases, such as neurofibromatosis types 1 and 2, which predispose to tumors of the peripheral nerves and brain. Recent advances in molecular biology have greatly enhanced the importance of studying cancer families. Newly developed molecular probes have been applied to map the loci of several human cancer genes. The studies have also revealed a new class of human oncogenes, the tumor suppressor genes. These genes normally function by suppressing the tumor phenotype. When inactivated or deleted in germinal cells, they can be transmitted to subsequent generations and predispose to cancer among carriers in the family. At the molecular level, these carriers have inherited a structural abnormality in one allele of a recessive oncogene, and loss of the second allele at the locus results in tumor development. The first tumor suppressor that has been isolated is the retinoblastoma gene on chromosome 13q14. Studies indicate that this gene is involved in the development of many more human cancers than had been appreciated previously on the basis of clinical observations. Presently, the identification of cancer families can be applied to genetic counseling, the in-utero diagnosis of carriers, and early disease detection. In familial cancers that are triggered by environmental carcinogens, patient education regarding the avoidance of harmful exposures can help prevent or delay the onset of neoplasia.

CpG island clones from a deletion encompassing the gene for adenomatous polyposis coli

Adenomatous polyposis coli (APC), a dominantly inherited disorder, has been mapped to chromosome 5q15-q21 by family linkage studies. Cells from patients with deletions in this region, in one case associated with polyposis in a family, have been used to construct human hamster hybrid cell lines that retain either the normal or deleted chromosome 5. These lines have been used to identify markers from the region of the polyposis gene obtained by cloning the ends of 0.5- to 2-megabase BssHII fragments purified by pulsed-field gel electrophoresis. Three markers are described that map within the deletions and must therefore be close to the APC gene.