Recurrent and founder mutations in the PMS2 gene.

Germline mutations in PMS2 are associated with Lynch syndrome (LS), the most common known cause of hereditary colorectal cancer. Mutation detection in PMS2 has been difficult due to the presence of several pseudogenes, but a custom-designed long-range PCR strategy now allows adequate mutation detection. Many mutations are unique. However, some mutations are observed repeatedly across individuals not known to be related due to the mutation being either recurrent, arising multiple times de novo at hot spots for mutations, or of founder origin, having occurred once in an ancestor. Previously, we observed 36 distinct mutations in a sample of 61 independently ascertained Caucasian probands of mixed European background with PMS2 mutations. Eleven of these mutations were detected in more than one individual not known to be related and of these, six were detected more than twice. These six mutations accounted for 31 (51%) ostensibly unrelated probands. Here, we performed genotyping and haplotype analysis in four mutations observed in multiple probands and found two (c.137G>T and exon 10 deletion) to be founder mutations and one (c.903G>T) a probable founder. One (c.1A>G) could not be evaluated for founder mutation status. We discuss possible explanations for the frequent occurrence of founder mutations in PMS2.

Alleles of APC modulate the frequency and classes of mutations that lead to colon polyps.

Most inherited mutant alleles of the adenomatosis polyposis coli gene (APC) cause the appearance of large numbers of colon polyps, the familial polyposis syndrome. (These mutant alleles are designated APCp alleles.) A subset of APC mutations, the attenuated or APC(AP) alleles, predispose to only a few colon polyps. This leads to the hypothesis that if mutation of the inherited normal allele is rate limiting in polyp development, the increased number of polyps associated with the APCp allele indicates that the frequency of mutations that can lead to polyp formation is higher among APCp carriers than among APC(AP) carriers. We have previously suggested that the APC protein might modulate the frequency of mutations, such as loss of heterozygosity (LOH), necessary for colon polyp formation. We thus reasoned that tumours from patients who carry an APC(AP) allele might show a reduced frequency of LOH compared with tumours from patients who carry an APCp allele. Loss of AAPC mutant alleles is designated as LOH(AP). Screening of tumours from APC(AP) carriers revealed a reduction of LOH compared with that of an unselected group of polyposis patients. In fact, no loss of the inherited APC(N) allele was observed, although sequencing showed that the inherited APC(N) allele had frequently undergone point mutations and small deletions in the tumours. A low frequency loss of the inherited APC(AP) allele was seen. These findings support the suggestion that the APC(AP) allele has residual gene activity and that this activity modulates the spectrum and frequency of mutations that lead to adenoma formation.

Constitutional mismatch repair-deficiency syndrome presenting as colonic adenomatous polyposis: clues from the skin.

Constitutional mismatch repair-deficiency (CMMR-D) syndrome is an autosomal recessive condition characterized by hematologic malignancies, brain tumors, Lynch syndrome-associated cancers and skin manifestations reminiscent of neurofibromatosis type 1 (NF1). In contrast to Lynch syndrome, CMMR-D syndrome is exceptionally rare, onset typically occurs in infancy or early childhood and, as described in this report, may also present with colonic polyposis suggestive of attenuated familial adenomatous polyposis (AFAP) or MUTYH associated polyposis (MAP). Here we describe two sisters with CMMR-D syndrome due to germline bi-allelic MSH6 mutations. Both sisters are without cancer, are older than typical for this condition, have NF1 associated features and a colonic phenotype suspicious for an attenuated polyposis syndrome. This report highlights the role of skin examinations in leading to an underlying genetic diagnosis in individuals with colonic adenomatous polyposis, but without mutations associated with AFAP or MAP.

Mismatch repair polymorphisms and risk of colon cancer, tumour microsatellite instability and interactions with lifestyle factors.

BACKGROUND: Germline mutations in DNA mismatch repair (MMR) genes cause Lynch syndrome colon cancers. Less understood is the risk of colon cancer associated with common polymorphisms in MMR genes and the potential interacting role of lifestyle factors known to damage DNA. METHODS: A study was conducted to examine whether MLH1 (-93G>A and Ile219Val) and MSH6 (Gly39Glu) polymorphisms were associated with risk of colon cancer in data from 1609 colon cancer cases and 1972 controls. Genotype data were further stratified by microsatellite instability status, smoking, alcohol, Western diet, alcohol and obesity, to investigate potential heterogeneity. RESULTS: The MSH6 39Glu allele was associated with increased risk of colon cancer among men (Gly/Glu or Glu/Glu vs Gly/Gly, OR 1.27; 95% CI 1.04 to 1.54). Neither MLH1 polymorphism was associated with colon cancer risk overall. When stratified by microsatellite stability status, however, the MLH1 -93A allele was associated with a more than doubling in microsatellite instability (MSI)-positive colon cancer risk (AA vs GG, OR 2.47; 95% CI 1.48 to 4.11); no associations were observed between the MMR polymorphisms examined and MSI-negative colon cancer. Statistically significant interactions were observed between: MLH1 -93G>A and smoking (MSI-negative colon cancer only, p value interaction: 0.005); and MLH1 Ile219Val and Western diet (p value interaction: 0.03). CONCLUSIONS: The MSH6 Gly39Glu and MLH1 -93G>A polymorphisms were associated with risk of overall colon and MSI-positive colon cancers, respectively. Risk for colon cancer, stratified by MMR genotype, was further modified by smoking and Western diet.

Associations between cigarette smoking, lifestyle factors, and microsatellite instability in colon tumors.

BACKGROUND: Microsatellite instability (MSI) has been reported to occur in approximately 10%-15% of colon tumors. MSI is characterized by the presence of mutations in tandemly repeated DNA sequences known as microsatellites. Some individuals with unstable tumors have inherited mutations in mismatch repair genes, but MSI is also observed in sporadic colon cancer. It is unknown whether lifestyle factors associated with colon cancer, such as physical activity, body size, cigarette smoking, or use of aspirin and/or nonsteroidal anti-inflammatory drugs, contribute to MSI in sporadic tumors. METHODS: Data from a population-based, case-control study of colon cancer were used. Case subjects were between 30 and 79 years of age at the time of diagnosis and included both men and women. Questionnaire data were used to obtain information on lifestyle factors. Tumor MSI was determined with the use of a panel of 10 tetranucleotide repeats and two mononucleotide repeats. A total of 1510 case subjects had valid questionnaire data and tumor DNA from which we were able to obtain MSI status. Questionnaire data were compared with lifestyle factors reported by 2410 population-based control subjects. All statistical tests were two-sided. RESULTS: MSI-positive (MSI(+)) tumors were most common in older people and women and in the proximal colon. Patients with MSI(+) tumors were more likely to smoke 20 or more cigarettes a day than case subjects with MSI-negative (MSI(-)) tumors (odds ratio for being a smoker = 1.6 [95% confidence interval = 1.0-2.5] for men and 2.2 [95% confidence interval = 1.4-3.5] for women). The association between MSI(+) tumors and cigarette smoking was strongest among case subjects who started to smoke at a young age, smoked for 35 or more years, and were either current smokers or had stopped fewer than 15 years before diagnosis. A statistically significant linear trend of increased risk of MSI(+) tumors was observed with increasing amount smoked (P<.01). CONCLUSIONS: This study suggests that smoking cigarettes statistically significantly contributes to MSI in colon tumors. We estimate that approximately 21% of MSI in colon tumors may be attributable to cigarette smoking.

Alternatively spliced adenomatous polyposis coli (APC) gene transcripts that delete exons mutated in attenuated APC.

Reverse transcription-PCR combined with either (a) restriction enzyme digestion and repeat PCR or (b) ligase chain reaction has identified two new alternatively spliced transcripts of the adenomatous polyposis coli (APC) gene. In one of these transcripts exons 1-4 and the first 16 bases of exon 5 are deleted; in the other exons 2-4 and the first 16 bases of 5 are deleted. Both transcripts use an intraexonic splice acceptor in exon 5. These transcripts delete exons mutated in attenuated APC (3 and 4) and could account for the reduction in severity of this variant.

Demonstration of promoter activity and alternative splicing in the region 5' to exon 1 of the APC gene.

Screening of fetal brain and fetal retina complementary DNA (cDNA) libraries and exon-connection experiments using brain cDNA have identified three exons 5' to exon 1 of the adenomatous polyposis coli gene. The exons are termed (from 5'-3') 0.3, 0.1, and 0.2; exons 0.1 and 0.2 are contiguous genomically. Library screening revealed alternatively spliced cDNAs containing the following combinations of 5'-exons: 0.3 + 1 + 2, 0.3 + 2, 0.1 + 0.2 + 1 + 2, and 0.1 + 1 + 2. Exon-connection experiments also identified these four forms in mRNAs from tissues and cultured cell lines, along with two additional forms, 0.1 + 0.2 + 2 and 0.1 + 2. The multiple splice forms may lead to proteins of differing activity; for example, products derived from cDNAs without exon 1 will lack most of a heptad-repeat domain that supports formation of homodimers. No mRNA species combining 0.3 with either 0.1 or 0.2 were identified. The existence of two apparently separate 5'-ends of APC suggests the possibility of two independent promoters. The genomic sequence adjacent to exon 0.3 confers promotor activity when cloned in a chloramphenicol acetyltransferase expression vector and transfected into a colon cancer cell line.

Beta-catenin mutations are more frequent in small colorectal adenomas than in larger adenomas and invasive carcinomas.

Loss of serine or threonine phosphorylation sites from exon 3 of beta-catenin has been identified in approximately half of colorectal tumors which lack adenomatous polyposis coli (APC) mutations, but the overall contribution of beta-catenin mutations to sporadic colorectal tumorigenesis is unclear. We therefore used PCR to amplify and sequence exon 3 of beta-catenin from 202 sporadic colorectal tumors. Exon 3 beta-catenin mutations were identified in 6 of 48 small (< 1 cm) adenomas, 2 of 82 large (> or =1 cm) adenomas, and 1 of 72 invasive carcinomas. Eight of the nine mutations, including all of those in the small adenomas and the invasive cancer, involved loss of serine or threonine phosphorylation sites. The percentage of beta-catenin mutations in small adenomas (12.5%) was significantly greater than that in large adenomas (2.4%) and invasive cancers (1.4%; P = 0.05 and P = 0.02, respectively). We conclude that mutation of beta-catenin can be an early, perhaps initiating, event in colorectal tumorigenesis. Small adenomas with beta-catenin mutations do not appear to be as likely to progress to larger adenomas and invasive carcinomas as other adenomas, however, with the result that beta-catenin mutations are only rarely seen in invasive cancers. This suggests that APC and beta-catenin mutations are not functionally equivalent, and that the APC gene may have other tumor suppressor functions besides the degradation of beta-catenin.

A molecular variant of the APC gene at codon 1822: its association with diet, lifestyle, and risk of colon cancer.

The adenomatous polyposis coli (APC) gene is important in the etiology of colon cancer. Although germ-line mutations of this gene rarely occur in the population, less penetrant variants of the gene have been reported. One variant, producing an aspartate to valine change at codon 1822 (D1822V) [corrected] has been previously reported as having an allele frequency of 10%. The purpose of this study was to determine whether this D1822V [corrected] variant of the APC gene is associated with colon cancer and whether its association is influenced by other genetic or environmental factors. We used data collected as part of a multicenter study of 1,585 incident cases of colon cancer and 1,945 age- and sex-matched population-based controls to evaluate genetic, dietary, and environmental associations with the D1822V [corrected] variant of the APC gene. The frequency of the valine/valine allele at codon 1,822 was 22.8% in this population. In the control population, 61.5% were homozygote wild type, 33.3% were heterozygotes, and 5.2% were homozygote variant. Cases were slightly less likely to have the homozygous variant APC genotype than were controls [odds ratio (OR), 0.8; 95% confidence interval (CI), 0.6-1.1]; for those diagnosed after age 65, the homozygous APC variant was associated with reduced risk of colon cancer (OR, 0.6; 95% CI, 0.4-1.0). Assessment of the homozygous APC variant with dietary, genetic, and environmental factors showed that individuals with this genotype were at lower risk if they consumed a low-fat diet (OR, 0.2; 95% CI, 0.1-0.5) relative to those who were homozygous wild type and ate a high-fat diet. This finding was specific to a low-fat diet and was unrelated to other dietary variables. These results suggest that the codon 1,822 variant of the APC gene may have functional significance. Individuals who have the valine/valine variant of this gene may be at reduced risk of colon cancer if they eat a low-fat diet.

Associations between dietary intake and Ki-ras mutations in colon tumors: a population-based study.

Ki-ras mutations are thought to be early events in the carcinogenic process leading to colon tumors. Dietary factors associated with colon cancer may be associated with these mutations. Data from a population-based, multicenter, case-control study of colon cancer were used to determine whether dietary factors are associated with Ki-ras mutations. Ki-ras mutations were detected by direct sequencing of codons 12 and 13 of the Ki-ras gene on exon 1 from DNA obtained from archival tissue. Ki-ras data were available for 1428 cases with valid interview data; data from 2410 controls were available for comparison with cases positive and negative for Ki-ras mutations. Mutations in the Ki-ras gene were detected in 32% of tumors. Of these mutations, 32.8% were G-->A transitions in the second base of codon 12 (2G-->A). Other than cruciferous vegetables, there were no nutrients or foods associated specifically with Ki-ras mutations [odds ratio (OR) for high intake relative to low intake, 0.7; 95% confidence interval (CI), 0.5-1.0]. However, evaluation of specific types of Ki-ras mutations revealed that for each of the most common types of mutation, dietary associations existed. Dietary factors involved in DNA methylation pathways were associated with 2G-->A mutations. Comparison of individuals with and without Ki-ras mutations revealed that individuals with low levels of dietary folate (OR, 0.7; 95% CI, 0.4-1.3), vitamin B6 (OR, 0.5; 95% CI, 0.3-1.0), vitamin B12 (OR, 0.6; 95% CI, 0.3-1.1), and high levels of alcohol (OR, 0.7; 95% CI, 0.4-1.1) were less likely to have a 2G-->A mutation. Individuals with high levels of dietary carbohydrate (OR, 2.0; 95% CI, 0.9-4.4) and a high glycemic index (OR, 1.9; 95% CI, 0.8-4.6) were more likely to have a G-->A transition mutation in the second base of codon 13 (5G-->A). Individuals with high levels of dietary fat (OR, 1.6; 95% CI, 0.8-3.2), saturated fat (OR, 1.7; 95% CI, 0.8-3.5), and monounsaturated fat (OR, 1.9; 95% CI, 1.0-3.7) were more likely to harbor a 2G-->T mutation. Low levels of cruciferous vegetable intake and high levels of processed meat intake also were associated with fewer 5G-->A, as reflected by the ORs (OR, 0.4; 95% CI, 0.2-1.0 and OR, 0.4; 95% CI 0.2-0.8, respectively). These data suggest that diet may be involved in disease pathways represented by specific Ki-ras mutations. However, given the limited information currently available on associations between specific genetic mutations in colon tumors and diet, these findings also should be viewed as hypothesis generating.

Estrogens reduce and withdrawal of estrogens increase risk of microsatellite instability-positive colon cancer.

There are sex differences in the occurrence of microsatellite instability (MSI) in colon tumors. Taken together with the epidemiological evidence that hormone replacement therapy (HRT) and, less consistently, parity, are inversely associated with colon cancer, it has been hypothesized that estrogens are associated with MSI. The purpose of this study was to evaluate sex-specific differences in the prevalence of MSI in colon tumors and to determine whether reproductive history and hormonal exposures are associated with MSI. Using data from a population-based case-control study of 1836 cases with MSI data and 2410 population-based controls, we evaluated sex, reproductive factors, and hormone exposure in relation to the presence or absence of MSI in tumors. MSI was evaluated by a panel of 10 tetranucleotide repeats, the noncoding mononucleotide repeat BAT-26, and the coding mononucleotide repeat in transforming growth factor beta receptor type II (TGFbetaRII). Exposure data on reproduction, hormone use, obesity, and physical activity were obtained from an interviewer-administered questionnaire. Women were less likely then men to have MSI+ tumors at a young age and more likely to have unstable tumors at an older age; we observed a significant interaction (P < 0.01) between age, sex, and MSI. Evaluation of reproductive factors showed that women who had ever been pregnant had half the risk of MSI+ tumors compared with women who had never been pregnant. In complementary fashion, total ovulatory months were associated with an increased risk of MSI+ tumors [odds ratio (OR), 2.1; 95% confidence interval (CI), 1.1-4.0 comparing MSI+ versus MSI- tumors]. Age at first and last pregnancy did not influence the association. The observed associations were strongest among women <60 years of age at the time of diagnosis. Having used oral contraceptives was associated with a lower risk of MSI+ tumors (OR, 0.7; 95% CI, 0.4-1.2); recent users of HRT were at a reduced risk of MSI+ tumors (OR, 0.8; 95% CI, 0.5-1.4); and women who were former HRT users were at an increased risk of MSI+ tumors (OR, 1.8; 95% CI, 1.1-3.0). Obesity and lack of physical activity were associated with an elevated risk of both MSI+ (OR, 1.7; 95% CI, 0.7-3.3) and MSI- (OR, 2.2; 95% CI, 1.7-3.) tumors in men, but only with MSI- (OR, 1.5; 95% CI, 1.1-2.2) tumors in women. The excess of MSI+ tumors in women is explained by the excess of MSI+ tumors at older ages. Our data suggest that estrogen exposure in women protects against MSI, whereas the lack of estrogen in older women increases risk of instability. HRT in these older women may, again, reduce the risk of unstable tumors. A model for the way in which estrogens (endogenous, exogenous, and obesity-associated) modify the risk of MSI+ tumors is proposed.

Response of colon cancer cell lines to the introduction of APC, a colon-specific tumor suppressor gene.

The APC gene, mutations in which are responsible for the inherited colon cancer syndrome adenomatous polyposis coli (APC), is described as a tumor suppressor gene. A full-length, wild-type APC gene was introduced by transfection into three human colon carcinoma cell lines, each characterized for mutations at loci involved in colon tumor formation. The response of each cell line to the introduction of APC differed with the genotype of the cell line. Some of the cell clones derived from these transfections displayed altered morphologies; some showed suppression of tumorigenicity based on growth in soft agar and tumor formation in nude mice. One cell line, SW480, could not be stably transfected with the APC gene. These results provide the first direct evidence that the APC gene can alter the transformation properties of colon carcinoma cells.

Genetic abnormalities in sporadic parathyroid adenomas: loss of heterozygosity for chromosome 3q markers flanking the calcium receptor locus.

Inactivating mutations of the parathyroid cell calcium receptor (CaR) gene cause one form of familial benign/hypocalciuric hypercalcemia, and in homozygous form, cause neonatal severe primary hyperparathyroidism with parathyroid hyperplasia. Thus, we postulated that partial or total loss of CaR function might contribute to calcium insensitivity or even stimulate cell proliferation in sporadic parathyroid adenomas (PAds). To examine this possibility, we sought loss of heterozygosity (LOH) for markers flanking the CaR locus (3cen-3q21) in 35 PAds. We used 16 highly-polymorphic PCR-based markers in paired normal and tumor DNA, extracted from slices of archived surgical specimens. Nineteen to 24 of the DNA pairs were informative with at least one marker. In two informative pairs, we found LOH for markers D3S1303, D3S1267, or D3S1269, which are tightly-linked with and flank the CaR locus. In one tumor, deletion mapping confined the lost area between D3S1271 and D3S1238 (41.7 centimorgans, cM). In the other tumor, LOH spanned most of chromosome 3, ranging at least from D3S1307 to D3S1311 (271.4 cM). LOH was confirmed by repetition of the experiments and quantified by phosphorimaging. Thus, we found LOH encompassing the CaR locus in approximately 10% of sporadic PAds. These data are consistent with the hypothesis that loss of CaR function may occur in PAds, with functional consequences for calcium sensitivity and cell proliferation.

Relationship of Ki-ras mutations in colon cancers to tumor location, stage, and survival: a population-based study.

Some previous studies have demonstrated significant results between Ki-ras mutations and tumor stage, survival, and/or other clinical variables, whereas others have not. We therefore evaluated the significance of codons 12 and 13 Ki-ras mutations in a large population-based study of 1413 individuals with colon cancer. Ki-ras mutations were identified in approximately 32% of tumors. Codon 12 mutations were significantly more common in proximal than distal tumors (29.1% versus 20.5%; P < 0.01) and in tumors of advanced stage. Tumors from men were more likely to have transition mutations and codon 12 G-->A mutations. After adjusting for age and stage, the codon 13 G-->A mutation was associated with a 40% (95% confidence interval, 0.95-2.0) increase in short-term mortality from colon cancer. In conclusion, this population-based study demonstrates important relationships between Ki-ras mutations and stage, survival, tumor location, and gender.

NAT2, GSTM-1, cigarette smoking, and risk of colon cancer.

Cigarette smoking has been associated inconsistently with colon cancer. The extent to which genetic profile influences susceptibility to the inducement of colon cancer by cigarette smoking is not known. In this study, we evaluated the associations between smoking cigarettes and polymorphisms of the NAT2 and GSTM-1 genes using data obtained from an incident case-control study of 1993 cases of colon cancer and 2410 age- and sex- matched controls. Neither NAT2 nor GSTM-1 polymorphisms were significantly associated with colon cancer, except among older women, in whom the intermediate/rapid imputed phenotype was associated with increased risk of colon cancer [odds ratio (OR) = 1.4, 95% confidence interval (CI) = 1.0-1.81. Using several indicators of cigarette smoking, we observed no significant interaction between these genotypes and cigarette smoking and colon cancer. The major variation in association with colon cancer was from the amount of cigarette exposure, with those smoking a pack or more of cigarettes per day being at an approximately 40% increased risk of colon cancer; this association did not vary by genotype. However, those who stopped smoking 5-14 years prior to diagnosis and who where intermediate/rapid acetylators were at a slightly greater risk than those who were slow acetylators (for men, OR = 1.6, 95% CI = 1.0-2.4; for women, OR = 2.5, 95% CI = 1.4-4.4). Associations were similar when proximal and distal tumors were examined and separated for age at the time of diagnosis. The lack of an association does not rule out the possibility of other genetic polymorphisms interacting with cigarette smoke to cause colon cancer, nor does it take into account individual phenotypic variability.

Methylenetetrahydrofolate reductase, diet, and risk of colon cancer.

Individuals with different forms of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, carriers of the C677T mutation versus wild type, show differences in enzyme levels; these differences have been hypothesized to be related to DNA methylation and, perhaps, to the nucleotide pool size. Using data from an incident case-control study, we evaluated the combined effect of dietary intake of folate, methionine, vitamin B6, vitamin B12, and alcohol and various forms of the MTHFR gene on risk of colon cancer. Individuals homozygous for the variant form of the MTHFR gene (TT) had a slightly lower risk of colon cancer than did individuals who were wild type [CC, odds ratio (OR) = 0.8, 95% confidence interval (CI) = 0.6-1.1 for men; and OR = 0.9, 95% CI = 0.6-1.2 for women]. High levels of intake of folate, vitamin B6, and vitamin B12 were associated with a 30-40% reduction in risk of colon cancer among those with the TT relative to those with low levels of intake who were CC genotype. Associations were stronger for proximal tumors, in which high levels of intake of these nutrients were associated with a halving of risk among those with the TT genotype. The inverse association with high levels of these nutrients in those with the TT genotype was stronger among those diagnosed at an older age. Although imprecise, the inverse association with the low-risk diet that was high in folate and methionine and without alcohol was observed for both the TT genotype (OR = 0.4 95% CI = 0.1-0.9) and the CC/CT genotype (OR = 0.6, 95% CI = 0.4-1.0), but this association was not seen with the high-risk diet for either the TT or CC/CT genotype. Although associations were generally weak, these findings suggest that those with differing MTHFR genotypes may have different susceptibilities to colon cancer, based on dietary consumption of folate, vitamin B6, and vitamin B12.

Meat consumption, genetic susceptibility, and colon cancer risk: a United States multicenter case-control study.

Meat consumption may especially increase risk of colon cancer when the meat is prepared at high temperatures and consumed by subjects with an inherited susceptibility to well-done meat. In this United States case-control study, the association between meat consumption, genetic susceptibility, and colon cancer risk was studied. Meat consumption data were available from a detailed diet history questionnaire and from questions about methods of preparation. Molecular variants in the carcinogen-metabolizing genes NAT2 and GSTM1 were determined in DNA extracted from WBCs. A total of 1542 cases and 1860 population-based controls were included in these analyses. The amount of red and white meat consumed was not associated with overall colon cancer risk. Processed meat consumption was weakly positively associated with colon cancer risk in men only (odds ratio for highest versus lowest quintile of intake = 1.4, 95% confidence interval = 1.0-1.9). The frequency of fried, broiled, baked, or barbecued meat, use of drippings, and doneness of meat were not significantly associated with risk. The Mutagen Index, as an estimate for exposure to mutagenic or carcinogenic substances, was slightly positively associated with colon cancer risk in men (odds ratio = 1.3, 95% confidence interval = 1.0-1.7). No significant associations with colon cancer risk were observed for different NAT2 and GSTM1 gene variants. The observed associations with processed meat and the Mutagen Index were strongest for those with the intermediate or rapid NAT2 acetylator phenotype. Associations were not markedly influenced by lack of the GSTM1 gene. This study provides little support for an association between meat consumption and colon cancer risk but does provide some, albeit not strong, evidence for a modifying effect of molecular variants of the NAT2 gene.

Microsatellite instability in sporadic colon cancer is associated with an improved prognosis at the population level.

Some previous studies have reported an improved prognosis in sporadic colon cancers with microsatellite instability, whereas others have not. In addition, relatively few of those reporting an improved prognosis controlled for tumor stage or were population-based. Therefore, we evaluated the relationship between microsatellite instability and prognosis, tumor stage, and other clinical variables in a population-based study of 1026 individuals. Microsatellite instability was determined by the noncoding mononucleotide repeat BAT-26 and the coding mononucleotide repeat in transforming growth factor-beta receptor type II. Significant relationships were seen between microsatellite instability and proximal tumor location, female gender, young and old age at diagnosis, poor histological differentiation, and low tumor stage (P < 0.01). There was a significant relationship between microsatellite instability and improved prognosis, even after adjusting for stage, with a reduction in the risk of death attributable to colon cancer of approximately 60%. Most of this risk reduction occurred in individuals with American Joint Committee on Cancer stage III tumors, although transforming growth factor-beta receptor type II mutations were associated with a significant reduction in colon cancer death in tumors with distant metastases. We conclude that microsatellite instability in sporadic colon cancer is associated with an improved prognosis at the population level.

The nonspecificity of histological findings reported for flat adenomas.

Flat adenomas have been reported to be associated with an increased risk of high grade dysplasia and with a genetic predisposition to numerous colonic polyps. Histological findings reported for flat adenomas are dysplastic glands superficial to nondysplastic glands and a thickness of dysplastic mucosa that does not exceed twice that of nondysplastic mucosa. We assessed the specificity of these histological findings with regard to a colonoscopically flat appearance in a series of 127 sequentially accessioned adenomas from 52 patients without adenomatous polyposis coli or inflammatory bowel disease. Thirty-two of the 127 adenomas (25%) from 20 of 52 patients (36%) showed the histological findings outlined above; none of these polyps was grossly flat and none had high grade dysplasia. The predictive values of these histological features for patients younger than 50 years old and for the presence of five or more polyps in a patient were 15% and 25%, respectively. We conclude that the histological findings previously reported for flat adenomas are not specific for that entity and are not uncommonly seen in grossly typical appearing adenomatous polyps. These histological findings also are not associated with high grade dysplasia. They can be seen in polyps from individuals without clinically recognized polyposis, and are relatively poor indicators of young age or increased polyp number, features that could potentially indicate a clinically unrecognized polyposis syndrome. The histological findings in and of themselves thus appear to confer no additional cancer risk to the individual or to the individual's family members over and above that associated with an adenoma.

Reported binding of monoclonal antibody RAP-5 to formalin-fixed tissue sections is not indicative of ras p21 expression.

RAP-5 is a monoclonal antibody that has been shown to be immunoreactive with human ras gene product p21 in solid-phase radioimmunoassays and Western blots. RAP-5 binding in excess of that of control monoclonal antibodies to formalin-fixed tissue sections of several types of human tumors has been reported, and this binding has been interpreted as indicating p21 expression. We report that high concentrations of control monoclonal antibodies duplicated exactly the immunohistochemical staining pattern of RAP-5 on formalin-fixed tissue sections and that RAP-5 staining was not competitively inhibited by either the portion of p21 it was raised against or by the thyroglobulin-conjugated peptide used as immunogen. In an enzyme-linked immunosorbent assay, RAP-5 also showed greater nonspecific binding to poly-L-lysine and to polystyrene wells than did control antibodies. We conclude that RAP-5 binding to formalin-fixed tissue sections is nonspecific and not indicative of p21 expression.