Reassignment of a cancer family syndrome gene to chromosome 18

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.

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.

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.

Screening for large bowel neoplasms in individuals with a family history of colorectal cancer

Logistical problems associated with population screening for colorectal cancer are identified and the possibility of targeting screening to those with a familial predisposition to the disease is discussed. Evidence for a substantial genetic effect on the overall incidence of colorectal cancer is reviewed. The screening detection rate of colorectal neoplasms in relatives of patients with colorectal cancer has been shown to be higher than that expected in a non-selected population; the evidence that polypectomy will reduce future colorectal cancer risk in such individuals is explored. Recent advances in the molecular genetics of colorectal cancer susceptibility are reviewed; it is possible that a genetic test might be developed in the future which could identify at least a proportion of those at risk. Excluding financial considerations, the risk-benefit ratio of colonoscopy in a screened population is intimately related to the remaining risk of colorectal cancer in those who undergo the examination. At present, patients undergoing colonoscopy to investigate a positive faecal occult blood (FOB) test as part of a population-based screening programme include individuals with a familial predisposition as well as those without. About 20 per cent of all cases of colorectal cancer are associated with an obvious genetic predisposition, and the risk of cancer in their relatives is high. Because false positives occur with Haemoccult, the residual risk to the population who are FOB positive but do not have a familial trait may be sufficiently low that the dangers of colonoscopy could outweigh the potential benefits. Scotland has a high incidence of colorectal cancer, and analysis of recent Scottish incidence data shows an actuarial lifetime risk of developing this disease of one in 23 for men and one in 33 for women. As a family history of the disease increases that risk by two to four times and the neoplasms arise throughout the colon in such a group, there may be a case for offering colonoscopy to all first-degree relatives of those under 50 years of age at diagnosis, if not of all index cases of colorectal cancer.

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.

Correlation between in vitro tetraploidy in skin fibroblasts and development of sporadic colorectal carcinomas

In vitro tetraploidy (IVT) in skin fibroblasts cultures measured by flow cytometry was compared with histological type and degree of dysplasia in 22 patients with adenomas of the colon and rectum. Furthermore, IVT was compared with stage and differentiation in 36 patients with carcinoma of the colon and rectum. In vitro tetraploidy in skin fibroblasts was correlated to type as well as dysplasia in adenomas and differentiation in carcinomas but was not correlated to Dukes' stage in carcinomas. Skin fibroblast genetic instability, expressed as increased IVT (IVT+), has been reported to reflect a genetic predisposition to colorectal cancer in the hereditary nonpolyposis colorectal cancer syndrome. Because IVT+, which appears to be associated with the progression of adenomas to carcinomas, also is found in many of the non-syndrome colorectal cancers, we suggest that development of colorectal cancer is considerably influenced by the constitutive genetic instability of the autosomal dominant colorectal cancer syndromes.