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S R Hamilton

Publications and source records attributed to S R Hamilton.

At least 109 records · Page 6Linked to original sources
PubMed1996

Pigmented ocular fundus lesions and APC mutations in familial adenomatous polyposis.

BACKGROUND: Familial adenomatous polyposis (FAP) results from a germline mutation in the adenomatous polyposis coli (APC) gene on chromosome 5q21. The extracolonic manifestations of FAP include pigmented ocular fundus lesions (POFLS), cutaneous cysts, osteomas, occult radio-opaque jaw lesions, odontomas, desmoids, and extracolonic cancers. POFLS are present at birth in about 80% of patients with FAP and are excellent clinical congenital markers for the disease. We studied the distribution of POFLS by number and APC mutation in families of the Johns Hopkins Polyposis Registry. MATERIALS AND METHODS: Of the 51 families with FAP, 42 (82%) had an identifiable APC mutation. We correlated the presence/absence and distribution by number of POFLS with the type and location of the mutation in the APC gene in 21 families where an ocular examination had been performed in at least one affected member, and where a systematic search for mutations in the APC gene had been undertaken. Families were considered POFL-positive if the average number of lesions per patient was three or more, or if at least one family member had three or more lesions. RESULTS: Fifteen of the 21 families (71.4%) were POFL-positive. Mutations of the APC gene were detected in 15 of the 21 families. Of these, 12 (80%) were POFL-positive. Families with mutations at condons 215 (exon 5) and 302 (exon 8) were POFL-negative. Families with mutations at condons 541, 625, 1055, 1059, 1061, 1230, 1309, 1465, and 1546 (exons 12-15) were POFL-positive. One patient with a mutation at codon 2621 (exon 15) had no POFLS. CONCLUSIONS: Mutations in exons 1-8 and the distal portion of exon 15 of the APC gene are associated with a POFL-negative phenotype, while those in exons 10 to the proximal portion of exon I5 are generally associated with a POFL-positive

Adenomatous Polyposis Coli↗
PubMed1996

Early alteration of cell-cycle-regulated gene expression in colorectal neoplasia.

Aberrant crypt foci with dysplasia are thought to be the first detectable lesions of colorectal neoplasia. Because cell cycle disruption appears crucial for tumorigenesis, we analyzed the immunohistochemical expression patterns of the prototype cyclin-dependent kinase inhibitor p21 WAF1/CIP1 and the proliferation marker Ki67 in the early stages of colorectal tumorigenesis. In colorectal epithelium, p21 WAF1/CIP1 expression was undetectable in the lower third of the crypts, where Ki67 was expressed, but then sharply increased as cells passed out of the proliferating zone and migrated toward the humen. Hyperplastic polyps retained this normal compartmentalized pattern. In contrast, markedly decreased p21 WAF1/CIP1 immunostaining was observed in dysplastic aberrant crypt foci as well as in small adenomas. Moreover, the compartmentalization of Ki67 and p21 WAF1/CIP1 was lost, as Ki67 expression extended into the small p21-expressing zone at the top of the crypts. These data suggest that the dysregulated expression of cell-cycle-controlling genes and the consequent release from normal cell cycle controls may represent an essential early step in colorectal neoplasia.

Adenomatous Polyposis Coli↗
PubMed1996

Relationship between CD44 expression and cell proliferation in epithelium and stroma of colorectal neoplasms.

The cell surface glycoprotein CD44 is expressed primarily in the region of cell replication in the lower crypt epithelium of colorectal mucosa, and its expression is markedly increased in colorectal neoplasms, suggesting that expression is linked to proliferation. The association between CD44 expression and replication in individual cells was therefore analyzed by double-label immunohistochemistry for CD44 and the cell-cycle-dependent protein proliferating cell nuclear antigen (PCNA). Enhanced expression of CD44 in colorectal neoplasms occurred not only in epithelial cells but also in stromal cells, including lymphocytes and macrophages. On a topographical basis, the cellular localization of CD44 and PCNA were commonly different. Quantitatively, in all cell types studied (epithelial cells and stroma of colorectal mucosa, adenomas, and carcinomas) PCNA was present most frequently in cells lacking CD44. Statistical analysis by logistic regression models indicated that cells negative for CD44 had a higher probability of being positive for PCNA than did cells positive for CD44 (P < 0.001). These data suggest that the enhanced level of CD44 in colorectal neoplasms is asynchronous with cell replication and reflects mechanisms that act on nonproliferative stromal lymphocytes and other mononuclear cells as well as the epithelial cells.

Adult↗
PubMed1995

Topological control of p21WAF1/CIP1 expression in normal and neoplastic tissues.

The p53-regulated gene product p21WAF1/CIP1 is the prototype of a family of small proteins that negatively regulate the cell cycle. To learn more about p21WAF1/CIP1 regulation in vivo, monoclonal antibodies were developed for immunohistochemistry. These revealed that p21WAF1/CIP1 expression followed radiation-induced DNA damage in human skin in a pattern consistent with its regulation by p53. A detailed comparison of the human, rat, and mouse p21WAF1/CIP1 promoter sequences revealed that this induction was probably mediated by conserved p53-binding sites upstream of the transcription start site. In unirradiated tissues, p21WAF1/CIP1 expression was apparently independent of p53 and was observed in a variety of cell types. Moreover, there was a striking compartmentalization of p21WAF1/CIP1 expression throughout the gastrointestinal tract that correlated with proliferation rather than differentiation. As epithelial cells migrated up the crypts, the Ki67-expressing proliferating compartment near the crypt base ended abruptly, with the coincident appearance of a nonproliferating compartment expressing p21WAF1/CIP1. In colonic neoplasms, this distinct compartmentalization was largely abrogated. Cell cycle inhibitors are thus subject to precise topological control, and escape from this regulation may be a critical feature of neoplastic transformation.

Adenoma↗
PubMed1995

Mismatch repair deficiency in phenotypically normal human cells.

Tumor cells in patients with hereditary nonpolyposis colorectal cancer (HNPCC) are characterized by a genetic hypermutability caused by defects in DNA mismatch repair. A subset of HNPCC patients was found to have widespread mutations not only in their tumors, but also in their non-neoplastic cells. Although these patients had numerous mutations in all tissues examined, they had very few tumors. The hypermutability was associated with a profound defect in mismatch repair at the biochemical level. These results have implications for the relation between mutagenesis and carcinogenesis, and they suggest that mismatch repair deficiency is compatible with normal human development.

Base Sequence↗
PubMed1995

Inhibition of apoptosis during development of colorectal cancer.

Colorectal tumorigenesis proceeds through an accumulation of specific genetic alterations. Studies of the mechanism by which these genetic changes effect malignant transformation have focused on the deregulation of cell proliferation. However, colorectal epithelial homeostasis is dependent not only on the rate of cell production but also on apoptosis, a genetically programmed process of autonomous cell death. We investigated whether colorectal tumorigenesis involved an altered susceptibility to apoptosis by examining colorectal epithelium from normal mucosa, adenomas from familial adenomatous polyposis, sporadic adenomas, and carcinomas. The transformation of colorectal epithelium to carcinomas was associated with a progressive inhibition of apoptosis. The inhibition of apoptosis in colorectal cancers may contribute to tumor growth, promote neoplastic progression, and confer resistance to cytotoxic anticancer agents.

Adenomatous Polyposis Coli↗
PubMed1995

The molecular basis of Turcot's syndrome.

BACKGROUND: Turcot's syndrome is characterized clinically by the concurrence of a primary brain tumor and multiple colorectal adenomas. We attempted to define the syndrome at the molecular level. METHODS: Fourteen families with Turcot's syndrome identified in two registries and the family originally described by Turcot and colleagues were studied. Germ-line mutations in the adenomatous polyposis coli (APC) gene characteristic of familial adenomatous polyposis were evaluated, as well as DNA replication errors and germline mutations in nucleotide mismatch-repair genes characteristic of hereditary nonpolyposis colorectal cancer. In addition, a formal risk analysis for brain tumors in familial adenomatous polyposis was performed with a registry data base. RESULTS: Genetic abnormalities were identified in 13 of the 14 registry families. Germ-line APC mutations were detected in 10. The predominant brain tumor in these 10 families was medulloblastoma (11 of 14 patients, or 79 percent), and the relative risk of cerebellar medulloblastoma in patients with familial adenomatous polyposis was 92 times that in the general population (95 percent confidence interval, 29 to 269; P < 0.001). In contrast, the type of brain tumor in the other four families was glioblastoma multiforme. The glioblastomas and colorectal tumors in three of these families and in the original family studied by Turcot had replication errors characteristic of hereditary nonpolyposis colorectal cancer. In addition, germ-line mutations in the mismatch-repair genes hMLH1 or hPMS2 were found in two families. CONCLUSIONS: The association between brain tumors and multiple colorectal adenomas can result from two distinct types of germ-line defects: mutation of the APC gene or mutation of a mismatch-repair gene. Molecular diagnosis may contribute to the appropriate care of affected patients.

Adenomatous Polyposis Coli↗
PubMed1995

The effects of sulindac on colorectal proliferation and apoptosis in familial adenomatous polyposis.

BACKGROUND & AIMS: The mechanism by which sulindac causes regression of adenomas in patients with familial adenomatous polyposis (FAP) is unclear. Conflicting data on the drug's effects on colorectal epithelial proliferation have been reported. An alternative mechanism, and one not previously studied, is via induction of colorectal epithelial cell apoptosis (programmed cell death). This hypothesis was tested by studying the effects of sulindac on colorectal epithelial proliferation and apoptosis in patients with FAP. METHODS: Cell proliferation was studied via immunohistochemistry for cell nuclear antigen in a group of 22 patients randomized to either sulindac (150 mg twice a day) or placebo in a previously published trial. The rectal epithelium from 7 additional patients with FAP treated with sulindac was examined by flow cytometry to assess changes in cell-cycle distribution and apoptosis. RESULTS: Although sulindac caused a significant decrease in polyp size and number, there was no significant change in cytokinetic variables or cell cycle distribution 3 months after treatment. However, the subdiploid apoptotic fraction was increased significantly 3 months after treatment with sulindac (31.3% +/- 4.8% compared with 10% +/- 4.3% at baseline; P = 0.01). CONCLUSIONS: Our findings suggest that sulindac does not affect colorectal epithelial proliferation and that its effects in patients with FAP may instead result from induction of apoptosis.

Adenomatous Polyposis Coli↗
PubMed1995

Mismatch repair gene defects in sporadic colorectal cancers with microsatellite instability.

Microsatellite instability has been observed in both sporadic and hereditary forms of colorectal cancer. In the hereditary form, this instability is generally due to germline mutations in mismatch repair (MMR) genes. However, only one in ten patients with sporadic tumours exhibiting microsatellite instability had a detectable germline mutation. Moreover, only three of seven sporadic tumour cell lines with microsatellite instability had mutations in a MMR gene, and these mutations could occur somatically. These results demonstrate that tumours can acquire somatic mutations that presumably do not directly affect cell growth but result only in genetic instability. They also suggest that many sporadic tumours with microsatellite instability have alterations in genes other than the four now known to participate in MMR.

Adult↗
PubMed1995

Genetic instability occurs in the majority of young patients with colorectal cancer.

Replication errors (RER) associated with genetic instability have been found in cancers of several different types and particularly in the tumours of patients with hereditary non-polyposis colorectal cancer (HNPCC). We have here determined the prevalence of such instability in relation to age among patients without HNPCC. Colorectal cancers (CRCs) in the majority of patients 35 years of age or younger exhibited instability (58% of 31 patients), whereas CRCs from patients older than 35 uncommonly did (12% of 158, p < 0.0001). Twelve of the patients under 35 with instability were evaluated for alterations of mismatch repair genes, and five were found to harbour germline mutations. These data suggest that the mechanisms underlying tumour development in young CRC patients differ from those in most older patients, regardless of HNPCC status. The results have important implications for genetic testing and management of young CRC patients and their families.

Adult↗
PubMed1994

Inactivation of both APC alleles in human and mouse tumors.

Germline mutations of the adenomatous polyposis coli (APC) gene lead to multiple intestinal tumors in familial adenomatous polyposis patients and in multiple intestinal neoplasia (Min) mice. Current models predict that inactivation of the remaining normal allele of a tumor suppressor gene is rate limiting for tumor formation, but this has been difficult to prove. While examination of colorectal adenomas from familial adenomatous polyposis patients identified somatic inactivating mutations of the second allele in the majority of tumors (19 of 24), the absolute requirement for an early inactivating event could not be demonstrated. In contrast, inactivation of the remaining allele of the murine APC (Apc) could be demonstrated in 100% (30 of 30) of tumors from Min mice. Moreover, inactivation was observed in the earliest recognizable phase of tumors, including some lesions containing as few as two dysplastic crypts. These results suggest that the mutation of the second APC allele is an early event in Min and familial adenomatous polyposis tumorigenesis, supporting Knudson's hypothesis.

Adenomatous Polyposis Coli↗
PubMed1994

Molecular determinants of dysplasia in colorectal lesions.

One hallmark of malignant potential is dysplasia, the disruption of normal morphology. While it is generally recognized that cancer is the result of a series of genetic changes, the relationship of these alterations and their timing to the advent of dysplasia remains obscure. To address this issue, 54 small benign colorectal lesions of various malignant potential were analyzed for APC and K-RAS mutations, two alterations which have been implicated in the early stages of colorectal tumorigenesis. APC mutations were closely associated with dysplasia. In contrast, K-RAS mutations were found to be remarkably common in small nondysplastic lesions which apparently have a limited potential to progress to larger tumors. These results provide evidence that the nature and order of genetic changes can have a specific impact on both tumor morphology (e.g., dysplasia) and the likelihood of tumor progression.

Base Sequence↗
PubMed1994

hMSH2 mutations in hereditary nonpolyposis colorectal cancer kindreds.

It has recently been shown that hereditary nonpolyposis colorectal cancer (HNPCC) is caused by hereditable defects in DNA mismatch repair genes. However, the fraction of HNPCC due to defects in any one repair gene and the nature of these mutations are not known. We analyzed 29 HNPCC kindreds for mutations in the prototype DNA mismatch repair gene hMSH2 by a combination of linkage analysis, polymerase chain reaction-based screening, and sequencing of the coding region. The complete intron/exon structure of the gene was ascertained to facilitate this analysis. The results suggest that at least 40% of classic HNPCC kindreds are associated with germline mutations in hMSH2 and that most of these mutations produce drastic alterations in the predicted protein product.

Amino Acid Sequence↗
PubMed1994

Allelic loss of chromosome 18q and prognosis in colorectal cancer.

BACKGROUND: Colorectal cancer occurs in approximately 150,000 people each year in the United States. Prognostic assessment influences the treatment of patients with colorectal cancer, including decisions about adjuvant therapy. We evaluated chromosome 18q allelic loss, a genetic event associated with tumor progression, as a prognostic marker for this disease. METHODS: We developed procedures to examine the status of chromosome 18q with microsatellite markers and DNA from formalin-fixed, paraffin-embedded tumors. Allelic loss of chromosome 18q was assessed in 145 consecutively resected stage II or III colorectal carcinomas. RESULTS: Among patients with stage II disease, the five-year survival rate was 93 percent in those whose tumor had no evidence of allelic loss of chromosome 18q and 54 percent in those with allelic loss; among patients with stage III disease, survival was 52 and 38 percent, respectively. The overall estimated hazard ratio for death in patients whose tumor had chromosome 18q allelic loss was 2.83 (P = 0.008) according to univariate analysis. Furthermore, chromosome 18q allelic loss remained a strong predictive factor (hazard ratio for death, 2.46; 95 percent confidence interval, 1.06 to 5.71; P = 0.036) after adjustment for all other evaluated factors, including tumor differentiation, vein invasion, and TNM stage. CONCLUSIONS: The status of chromosome 18q has strong prognostic value in patients with stage II colorectal cancer. The prognosis in patients with stage II cancer and chromosome 18q allelic loss is similar to that in patients with stage III cancer, who are thought to benefit from adjuvant therapy. In contrast, patients with stage II disease who do not have chromosome 18q allelic loss in their tumor have a survival rate similar to that of patients with stage I disease and may not require additional therapy.

Aged↗
PubMed1994

CD44 expression in colorectal adenomas is an early event occurring prior to K-ras and p53 gene mutation.

Neoplastic progression of colorectal epithelial cells from benign adenomas to malignant carcinomas appears to result from a series of genetic alterations involving both oncogenes and tumor suppressor genes. This progression was recently found to be associated with expression of splice variant isoforms of CD44, a cell surface hyaluronate receptor implicated in carcinogenesis. In this study we examined the relationship of CD44 expression to somatic genetic events in the adenoma-carcinoma sequence: point mutation of K-ras in codons 12 and 13 and overexpression of p53 protein as a marker of gene mutation. Among 22 small adenomas, CD44 was present in 9 (41%), of which only 1 contained a K-ras mutation. CD44 was absent in the other 2 small adenomas positive for K-ras mutation or p53 overexpression. In contrast to the early expression of CD44 in small adenomas, mutations of K-ras and p53 were detected preferentially in large adenomas and late-stage adenomas containing carcinoma. The frequent expression of CD44 prior to K-ras and p53 gene alterations in colorectal neoplasia suggests that activation of CD44 gene expression is related to earlier events in the adenoma-carcinoma sequence, possibly cell activation and proliferation following APC gene mutation or alteration of DNA methylation.

Adenoma↗
PubMed1994

An evaluation of six antibodies for immunohistochemistry of mutant p53 gene product in archival colorectal neoplasms.

Immunohistochemical detection of intranuclear p53 gene product may indicate mutation of the p53 suppressor gene on chromosome 17p. We used six commercially available antibodies for p53 immunohistochemistry on 19 archival colorectal neoplasms and compared the results with the mutation status of the p53 gene and 17p allelic deletion status. By Friedman's ranking analysis, use of mouse monoclonal antibody DO7 with Target Unmasking Fluid (TUF) for antigen retrieval was the most sensitive and specific procedure (P < 0.0001). Six of 7 cases with high expression (p53 Labeling Index > 30 per cent using a CAS 200 image analyser) had p53 mutation. Of seven tumours without expression (LI < 1 per cent), six had no mutation and one had a truncating mutation which prohibited nuclear localization of gene product. The low expression group (1 per cent < LI < 30 per cent, n = 5) consisted of three tumours without and two tumours with mutation. The sensitivity of high expression with the DO7-TUF method for p53 gene mutation was 67 per cent with specificity of 90 per cent, predictive value of a positive of 86 per cent, predictive value of a negative of 75 per cent, and efficiency of 79 per cent. This study suggests that immunohistochemistry is valuable for assessing p53 gene mutations in colorectal neoplasms, but further study is needed to elucidate the precise link between immunohistochemistry and molecular genetic alterations.

Antibodies↗
PubMed1994

Phenotypic variability of familial adenomatous polyposis in 11 unrelated families with identical APC gene mutation.

BACKGROUND/AIMS: Familial adenomatous polyposis is caused by germline mutation of the adenomatous polyposis coli (APC) gene. Affected individuals develop hundreds of colorectal adenomas at young age and can have extracolonic lesions. METHODS: This study evaluated the phenotype of 74 patients with familial adenomatous polyposis from 11 unrelated families with an identical 5-base pair deletion at codon 1309 of the APC gene. RESULTS: Polyp density in the sigmoid colon of 16 patients from 9 families varied from 3.8 to 13.1/cm2, and mean polyp diameter ranged from 1.4 +/- 0.1 to 2.7 +/- 0.1 mm. The distribution of colonic adenomas also varied, with diffuse polyposis in 6 patients but relative polyp sparing in the more proximal colon in 6 others. Age at diagnosis of colorectal cancer ranged from 19 to 62 years, but the mean age did not differ among the 4 families with multiple cases. Colorectal cancers occurred predominantly in the rectosigmoid (80%) but also in the more proximal colon. The percentage of patients affected by various extracolonic lesions differed widely among and within the 11 families (range, 0%-100%). CONCLUSIONS: APC gene mutation at codon 1309 results in intrafamily and interfamily phenotypic variation in familial adenomatous polyposis. Environmental and/or other genetic factors must play roles in the expression of germline APC gene mutations.

Adenomatous Polyposis Coli↗