Early-stage Adenoma Research Articles

Spectroscopic optical coherence tomography for classification of colorectal cancer in a mouse model.

Noninvasive diagnosis of the malignant potential of colon polyps can improve prevention of colorectal cancer without the need for time-consuming and expensive biopsies. This study examines the use of spectroscopic optical coherence tomography (OCT) to classify tissue from genetically engineered mouse models of early-stage adenoma (APC) and advanced adenocarcinoma (AKP) in which tumors are induced in the distal colon. The optical tissue properties of scattering power and scattering attenuation coefficient are evaluated by analyzing the imaging data collected from tissues. Classifications are generated using 2D linear discriminant analysis with high levels of discrimination obtained. The overall classification accuracy obtained was 91.5%, with 100% sensitivity and 96.7% specificity in separating tumors from benign tissue, and 77.8% sensitivity and 99.4% specificity in separating adenocarcinoma from nonmalignant tissue. Thus, this study demonstrates the clinical potential of using spectroscopic OCT for rapid detection of colon adenoma and colorectal cancer.

Detection of Streptococcus gallolyticus and Four Other CRC-Associated Bacteria in Patient Stools Reveals a Potential "Driver" Role for Enterotoxigenic Bacteroides fragilis.

Purpose Streptococcus gallolyticus subspecies gallolyticus (SGG) is an opportunistic pathogen causing invasive infections in the elderly often associated with colon neoplasia. The prevalence of SGG in the stools of patients with normal colonoscopy (control) was compared with patients with colorectal adenomas (CRA) or with carcinomas (CRC) from stages I to IV. The presence of the pks island encoding colibactin as well as other CRC-associated bacteria such as toxicogenic Bacteroides fragilis, Fusobacterium nucleatum, and Parvimonas micra was also investigated.Patients and MethodsFecal samples collected in France between 2011 and 2016 from patients with normal colonoscopy (n = 25), adenoma (n = 23), or colorectal cancer at different stages (n = 81) were tested by PCR for the presence of SGG, B. fragilis, F. nucleatum, P. micra, and the pks island. Relative quantification of SGG, F. nucleatum, and P. micra in stools was performed by qPCR.Results SGG prevalence was significantly increased in the CRC group. Our results also revealed i) a strong and significant increase of toxinogenic B. fragilis in patients with early-stage adenoma and of pks island at late-stage CRC and ii) increased levels of F. nucleatum and P. micra in the stools of CRC patients. Furthermore, the simultaneous detection of these five bacterial markers was only found in CRC patients.ConclusionsOur results indicate that the prevalence or relative levels of CRC-associated bacteria vary during CRC development. Among them, B. fragilis (bft+) was singled out as the sole pathobiont detected at the early adenoma stage.

Identification of microbial markers across populations in early detection of colorectal cancer

Associations between gut microbiota and colorectal cancer (CRC) have been widely investigated. However, the replicable markers for early-stage adenoma diagnosis across multiple populations remain elusive. Here, we perform an integrated analysis on 1056 public fecal samples, to identify adenoma-associated microbial markers for early detection of CRC. After adjusting for potential confounders, Random Forest classifiers are constructed with 11 markers to discriminate adenoma from control (area under the ROC curve (AUC) = 0.80), and 26 markers to discriminate adenoma from CRC (AUC = 0.89), respectively. Moreover, we validate the classifiers in two independent cohorts achieving AUCs of 0.78 and 0.84, respectively. Functional analysis reveals that the altered microbiome is characterized with increased ADP-l-glycero-beta-d-manno-heptose biosynthesis in adenoma and elevated menaquinone-10 biosynthesis in CRC. These findings are validated in a newly-collected cohort of 43 samples using quantitative real-time PCR. This work proves the validity of adenoma-specific markers across multi-populations, which would contribute to the early diagnosis and treatment of CRC.

Abstract 4597: 5-Hydroxymethylcytosine signatures in cell-free DNA as a potential biomarker for colorectal cancer andprecancerous adenoma

Abstract Colorectal cancer (CRC) is a serious malignancy with the third incidence and second mortality throughout the world. 5-Hydroxymethylcytosine (5hmC) signatures in circulating cell-free DNA (cfDNA) is an important epigenetic mark linked with human cancer pathogenesis. Here we explored the genome-wide 5-hydroxymethylcytosine profiling in the plasma cfDNA and tissue genomic DNA (gDNA) acquired from 101 samples (63 from plasma and 38 from tissues), collected from 21 CRC patients, 21 precancerous adenoma (AD) patients and 21 healthy control individuals (HC). 5hmC modifications exhibited distinct features in promoter and gene body regions in all 5 groups (3 groups from plasma and 2 groups from tissues), which offered a global overview of epigenetic changes of colon pathogenic statuses between early stage CRC and AD. Adenoma showed an independent property in the 5hmC profiles compared to cancer and healthy control. The 5hmC signatures in tumor were more comprehensive and could be divided into two clusters, one was similar to the healthy individuals and the other was similar to the AD patients. The results indicated that the candidate biomarkers to distinguish colorectal cancer from the blood-test population should be generated in two ways, one focused on the differential 5hmC features between CRC patients and healthy individuals; the other should detect the adenoma and tumor patients more extensive according to their precise pathological diagnosis and clinical information. Candidate cfDNA 5hmC biomarkers were further identified in the differential 5hmC modification regions between CRC and HC with a higher sensitivity than the classical CEA marker in non-invasive blood-based diagnosis. We suggested that the differentially enriched 5hmC regions in cfDNA were potential biomarkers to track colorectal cancer, even precancerous adenoma, with further large-scale follow-up studies. Citation Format: Zewen Xiao, Jiayan Wu, Chunlong Wu, Man Li, Fuming Sun, Lu Zheng, Gaojing Liu, Xiaoling Li, Zhiyuan Yun, Jiebing Tang, Yang Yu, Shengnan Luo, Wenji Sun, Xiaohong Feng, Qian Cheng, Xue Tao, Jian Bai, Lin Wu, Shuangxiu Wu, Ji Tao. 5-Hydroxymethylcytosine signatures in cell-free DNA as a potential biomarker for colorectal cancer andprecancerous adenoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4597.

Highly sensitive, non-invasive detection of colorectal cancer mutations using single molecule, third generation sequencing

Colorectal cancer (CRC) represents one of the most prevalent and lethal malignant neoplasms and every individual of age 50 and above should undergo regular CRC screening. Currently, the most effective preventive screening procedure to detect adenomatous polyps, the precursors to CRC, is colonoscopy. Since every colorectal cancer starts as a polyp, detecting all polyps and removing them is crucial. By exactly doing that, colonoscopy reduces CRC incidence by 80%, however it is an invasive procedure that might have unpleasant and, in rare occasions, dangerous side effects. Despite numerous efforts over the past two decades, a non-invasive screening method for the general population with detection rates for adenomas and CRC similar to that of colonoscopy has not yet been established. Recent advances in next generation sequencing technologies have yet to be successfully applied to this problem, because the detection of rare mutations has been hindered by the systematic biases due to sequencing context and the base calling quality of NGS.We present the first study that applies the high read accuracy and depth of single molecule, real time, circular consensus sequencing (SMRT-CCS) to the detection of mutations in stool DNA in order to provide a non-invasive, sensitive and accurate test for CRC. In stool DNA isolated from patients diagnosed with adenocarcinoma, we are able to detect mutations at frequencies below 0.5% with no false positives. This approach establishes a foundation for a non-invasive, highly sensitive assay to screen the population for CRC and the early stage adenomas that lead to CRC.

In vivo imaging of Lgr5-positive cell populations using confocal laser endomicroscopy during early colon tumorigenesis.

A diagnostic molecular marker for pre-neoplastic lesions, particularly before polyposis, is still lacking. Lgr5 has been broadly accepted as a marker for intestinal cancer stem cells. The aim of this study was to investigate the monitoring of Lgr5( + ) cells as a useful tool for the early diagnosis of premalignant lesions before polyp formation. In vivo molecular imaging was performed to examine colon tumorigenesis in Lgr5-EGFP mice treated with azoxymethane and dextran sodium sulfate. eGFP( +) Lgr5( +) regions in the descending colon were longitudinally monitored using side-view confocal endomicroscopy. Based on the eGFP signal intensity on the luminal surface, polyps were classified into two groups - Lgr5-high and Lgr5-low. White light colonoscopy was used to monitor polyp formation. Approximately 75 % of the polyps originated from foci containing Lgr5-eGFP( +) cells, whereas 25 % of the polyps emerged from Lgr5( -) foci. Among eGFP( +) foci, Lgr5-high foci grew faster than Lgr5-low foci. Polyps developed at Lgr5( +) regions. Luminal Lgr5 expression was correlated with the growth rate of early-stage adenomas. Lgr5 is a promising molecular marker for the early diagnosis of colon tumors.

Vasohibin-2 modulates tumor onset in the gastrointestinal tract by normalizing tumor angiogenesis.

BackgroundVasohibin-2 (VASH2) has been identified as an endogenous and vascular endothelial growth factor (VEGF)-independent angiogenic factor that is highly expressed in tumor cells. In the present study, we aimed to determine whether pre-existing vascular changes can be used to predict tumor transformation as benign or malignant. We sought to characterize microvascular changes and tumor development in the intestinal tract of Apc Min/+ mice and Apc Min/+ /Vash2 -/- mice.MethodsApc Min/+ mice provide a unique orthotopic model for the development of spontaneous adenomatous polyposis and subsequent carcinomas, a phenomenon termed the adenoma-carcinoma sequence. Apc Min/+ mice were mated with Vash2 -/- mice with a mixed C57BL/6 background and the resulting pups were screened for the Min mutation and for the Vash2 -/- gene by PCR. Intestinal tumors from Apc Min/+ mice and Apc Min/+ /Vash2 -/- mice were removed and either frozen or epon-embedded for subsequent analyses. For 3-dimensional imaging using confocal laser-scanning microscopy and transmission electron microscopy, cryosections were made, and immunofluorescent staining for various markers was performed.ResultsWe found that structural abnormalities in tumor vessels from benign tumors resembled those in malignant tumors. In addition, a novel angiogenic factor, vasohibin-2 (VASH2) protein, was detected around tumor blood vessels in late-stage adenomas and adenocarcinomas, but was absent from early-stage adenomas in Apc Min/+ mice. Tumors used to examine endogenous VASH2 (derived from CMT93 colon carcinomas) were less vascularized in Vash2-/- mice and were more regular than those seen in wild-type (WT) mice. In addition, tumors in Vash2-/- mice were smaller than those in WT mice. Furthermore, cross-breeding of mice homozygous for a deletion of Vash2 with mice heterozygous for the APC mutation resulted in animals that showed a significant decrease in the number of polyps in the small intestine.ConclusionWe propose that VASH2 may modulate the onset of tumors in the gastrointestinal tract by regulating tumor angiogenesis.

Relationship between tumor and peripheral blood NPRL2 mRNA levels in patients with colorectal adenoma and colorectal cancer

NPRL2 is a tumor suppressor gene involved in the progression of human cancer. The present study investigated whether NPRL2 expression correlates with colorectal cancer (CRC) progression. Colorectal tissue and peripheral blood samples were obtained from 62 patients with CRC, 38 patients with colorectal adenomas and 51 normal controls. NPRL2 mRNA levels in tissue samples and blood were measured using quantitative real-time PCR. NPRL2 protein expression was determined by immunohistochemistry. NPRL2 protein expression in CRCs was significantly lower than in the adenomas or normal colorectal tissue. NPRL2 mRNA expression was significantly decreased in adenomas compared with normal controls (P < 0.0001) and it was further decreased in colorectal tumors compared with adenomas (P < 0.0001). NPRL2 mRNA levels expression correlated with tumor stage. In addition, NPRL2 mRNA levels in the blood correlated with the levels detected in tumors. Furthermore, receiver operating characteristic (ROC) analysis showed that NPRL2 expression in blood could distinguish colorectal adenomas and CRCs from normal controls.NPRL2 mRNA expression in CRC tumor tissues and peripheral blood correlated with colorectal tumor progression. Based on our findings, we can conclude that NPRL2 mRNA blood levels could be a potentially useful marker for the detection of early stage adenomas and CRCs.

Abstract 2737: Spontaneous genomic alterations identified in a chimeric model of colorectal cancer guide effective combinatorial therapy.

Abstract Colon cancer is the second most common cause of cancer mortality in the western world. We generated a mouse model of colon cancer in which a conditional mutation of p53 is combined with inducible delta131-beta-Catenin over-expression in the intestinal epithelium. After 4-12 months of beta-Catenin induction, small adenomas and large solitary nodules of invasive adenocarcinomas developed in either the upper or lower intestinal tract, while the remainder of the intestine appeared normal. Molecular analysis revealed that EGFR and MET were expressed in advanced adenocarcinomas but not early stage adenomas. Although propagating mouse colon tumors has been very challenging, we nevertheless successfully established one tumor line through direct in vivo propagation in the kidney capsule. This tumor line, CB42, grew aggressively and metastasized to ancillary lymph nodes as well as the lung in a subcutaneous metastasis assay and grew in the liver when seeded there by intra splenic injection. Treatment with a MET inhibitor Crizotinib, had no effect on either primary tumor growth, or metastasis. By comparing the genome of CB42 with other colon tumors that did not propagate, we discovered an amplicon on chromosome five containing genes that correlated with propagation and metastasis. In addition, whole genome sequencing revealed that CB42 harbored a mutation in KRAS. Results from combination therapies against key genetic alterations will be presented. Citation Format: Yinghui Zhou, William M. Rideout, Angela Bressel, Sireesha Yalavarthi, Tong Zi, Anthony Monti, Steve Bottega, Bin Feng, M. Isabel Chiu, Marcus Bosenberg, Joerg Heyer. Spontaneous genomic alterations identified in a chimeric model of colorectal cancer guide effective combinatorial therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2737. doi:10.1158/1538-7445.AM2013-2737

Abstract 1008: Retinoids and TRAIL target early stage intestinal polyps in ApcMin/+ mice

Abstract The purpose of this study is to determine the optimal timing of treatment for a novel chemoprevention approach in a mouse model of Familial Adenomatous Polyposis (FAP). FAP is an autosomal dominantly inherited disorder caused by mutations in the tumor suppressor Apc (adenomatous polyposis coli) gene, which results in the formation of hundreds to thousands of polyps, predominantly in the colon and rectum. Left untreated, these polyps will form colorectal adenocarcinomas. Although surgical removal of the colon eliminates the colon cancer risk, these individuals are also at increased risk for other primary cancers, including tumors of the small intestine and stomach. Systemic chemopreventive interventions to specifically remove the pre-cancerous cells in these individuals could greatly improve their outcomes and quality of life. Recently, we have developed a new method based on the ability of combined retinoid and TRAIL (tumor necrosis factor related apoptosis inducing ligand) treatment to induce apoptosis and regression of intestinal polyps in ApcMin/+ mice, a mouse model of FAP. Treatment of these mice with retinoid causes an increase in TRAIL death receptors DR4 and DR5 as well as a concomitant decrease in the decoy receptors. APC deficiency leads to a decreased level of the anti-apoptotic protein FLIP (flice-like inhibitory protein). Thus, the combination of TRAIL and retinoid specifically targets APC deficient cells for apoptosis. Following up on these findings, we have tested the hypothesis that early stage adenomas of the intestine will respond more readily to TRAIL and retinoid treatment than those at a later stage. We used ApcMin/+ mice at either two months of age or five-six months of age. Each group of mice was given three treatments of retinyl acetate and TRAIL within one week. Following the last treatment, the intestine was harvested from each mouse and the polyps were counted. The number of polyps in each group of mice was compared with the polyp number in age matched non-treated mice. Results: When treated at two months of age, ApcMin/+ exhibit a nearly 50% decrease in polyp number following only one week of therapy. Conversely, ApcMin/+ treated at five-six months of age did not show any significant difference in polyp number compared to non-treated mice. Conclusion: Earlier stage adenomas respond more readily to the combined treatment of retinoid and TRAIL. This is likely due to additional mutations acquired by the later stage polyps. The cause of this resistance is a current area of study. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1008. doi:1538-7445.AM2012-1008

Inflammation and Colon Cancer

The connection between inflammation and tumorigenesis is well-established and in the last decade has received a great deal of supporting evidence from genetic, pharmacological, and epidemiological data. Inflammatory bowel disease is an important risk factor for the development of colon cancer. Inflammation is also likely to be involved with other forms of sporadic as well as heritable colon cancer. The molecular mechanisms by which inflammation promotes cancer development are still being uncovered and could differ between colitis-associated and other forms of colorectal cancer. Recent work has elucidated the role of distinct immune cells, cytokines, and other immune mediators in virtually all steps of colon tumorigenesis, including initiation, promotion, progression, and metastasis. These mechanisms, as well as new approaches to prevention and therapy, are discussed in this review.

Suppression of Familial Adenomatous Polyposis by CP-31398, a TP53 Modulator, in APCmin/+ Mice

p53 mutations occur in a large number of human malignancies. Mutant p53 is unable to affect downstream genes necessary for DNA repair, cell cycle regulation, and apoptosis. The styrylquinazoline CP-31398 can rescue destabilized mutant p53 expression and promote activity of wild-type p53. The present study examines chemopreventive effects of CP-31398 on intestinal adenoma development in an animal model of familial adenomatous polyposis. Effects were examined at both early and late stages of adenoma formation. Effects of CP-31398 on early-stage adenomas were determined by feeding 7-week-old female C57BL/6J-APC(min) (heterozygous) and wild-type C57BL/6J mice with American Institute of Nutrition-76A diets containing 0, 100, or 200 ppm of CP-31398 for 75 days. To examine activity toward late-stage adenomas, CP-31398 administration was delayed until 15 weeks of age and continued for 50 days. During early-stage intervention, dietary CP-31398 suppressed development of intestinal tumors by 36% (P < 0.001) and 75% (P < 0.0001), at low and high dose, respectively. During late-stage intervention, CP-31398 also significantly suppressed intestinal polyp formation, albeit to a lesser extent than observed with early intervention. Adenomas in treated mice showed increased apoptotic cell death and decreased proliferation in conjunction with increased expression of p53, p21(WAF1/CIP), cleaved caspase-3, and cleaved poly(ADP-ribose) polymerase. These observations show for the first time that the p53-modulating agent CP-31398 possesses significant chemopreventive activity in vivo against intestinal neoplastic lesions in genetically predisposed APC(min/+) mice. Chemopreventive activity of other agents that restore tumor suppressor functions of mutant p53 in tumor cells is currently under investigation.

Abstract LB-78: A randomized trial on folic acid supplementation and risk of recurrent colorectal adenoma

Abstract Results from two recently published randomized trials (Logan et al., 2008 and Cole et al., 2007) found little evidence for a protective effect of folic acid supplementation on the recurrence of colorectal adenomas. In one trial (Cole et al., 2007) folic acid supplementation even appeared to be non-significantly associated with higher risk of advanced adenoma. This following paper reports on results from another randomized controlled trial of folic acid (1000 micrograms/day) versus placebo among participants of two large prospective cohorts, the Health Professionals Follow-up Study (HPFS) and the Nurses’ Health Study (NHS), who had a previous diagnosis of colorectal adenoma. The primary endpoint of interest was any new diagnosis of adenoma during the study period (May, 1996 to March, 2003). 346 subjects were randomized to folic acid and 346 subjects to placebo for a period of three to up to 6 1/2 years. The incidence of at least one recurrent adenoma was not associated with folic acid supplementation (RR=0.86, 95% CI=0.64-1.16, p=0.32). There was some suggestion of an inverse association between folic acid supplementation and recurrent distal adenoma (multivariate adjusted relative risk (RR) =0.67, 95% confidence interval (CI)=0.39-1.15, p=0.14), and early stage adenoma (small and tubular) (RR=0.74, 95% CI=0.48-1.15, p=0.19), but none of the associations reached statistical significance. Advanced adenoma (large or adenomas with villous component) was not associated with folic acid supplementation, but the number of advanced cases was low (16 cases folate group, 18 cases placebo group; RR=0.96 95% CI=0.50-1.84, p=0.90). However, when associations were examined by folate blood concentrations drawn prior to time of randomization (&amp;lt;=7.5 ng/mL vs. &amp;gt;7.5 ng/mL) significant inverse associations were found for total recurrent adenoma (43 cases placebo, 32 cases folate, RR=0.64 (95% CI=0.43-0.96, p=0.03), distal adenoma (20 cases placebo, 9 cases folate, RR=0.36 (95% CI=0.14-0.61, p=0.001), early adenoma (22 cases placebo, 10 cases folate, RR=0.36 (95% CI=0.17-0.76, p=0.007), advanced adenoma (14 cases placebo, 9 cases folate, RR=0.48 (95% CI= 0.22-1.06, p=0.07) among those with low folate levels. No associations were found for participants with higher folate levels at baseline (at least one adenoma: 30 cases placebo, 30 cases folate, RR=1.30 (95% C=0.83-2.03, p=0.25). Occurrence of deaths, cancer and cardiovascular disease did not differ by treatment status. Our results do not support a protective effect of folic acid supplementation on the recurrence of colorectal adenomas; however, there may be some benefit on adenoma recurrence among those with a lower folate levels at baseline. The role of additional folic acid supplementation as a potential preventive measure for colorectal adenomas/cancer needs to be reevaluated especially with regard to dose and timing.

Plasma Vitamin B 6 and the Risk of Colorectal Cancer and Adenoma in Women

Vitamin B6, whose main circulating form is pyridoxal 5'-phosphate (PLP), is important in one-carbon metabolism, which is critical for DNA synthesis and DNA methylation, both of which are potentially involved in colorectal carcinogenesis. However, no previous epidemiologic studies have directly evaluated the association of plasma PLP with risk for colorectal neoplasia. We conducted a prospective nested case-control study of 32,826 female participants of the Nurses' Health Study who provided blood specimens in 1989-1990. From 1989-1990 to 2000 (1998 for adenoma), a total of 194 incident colorectal cancer cases and 410 incident colorectal adenoma cases were identified from medical records. Multivariable-adjusted relative risks (RRs) and 95% confidence intervals (CIs) were calculated using logistic regression. All statistical tests were two-sided. A suggestive inverse association was observed between plasma PLP concentration and risk for colorectal cancer when comparing the highest quartile versus the lowest (RR = 0.56, 95% CI = 0.31 to 1.01; P(trend) = .07); the association of PLP concentration with colon cancer was statistically significant (RR = 0.42, 95% CI = 0.21 to 0.85; P(trend) = .02). Both associations were statistically significant and stronger after controlling for intakes of folate, of multivitamins, and of methionine (for colorectal cancer, RR = 0.48, 95% CI = 0.25 to 0.92; P(trend) = .03; for colon cancer, RR = 0.38, 95% CI = 0.18 to 0.80; P(trend) = .01). Total vitamin B(6) intake was also statistically significantly inversely associated with colon cancer risk (RR = 0.51, 95% CI = 0.27 to 0.97; P(trend) = .007). There was a suggestive inverse association between plasma PLP concentration and advanced distal colorectal adenoma (RR = 0.65, 95% CI = 0.37 to 1.11; P(trend) = .08), but the association with early-stage adenoma was weaker (RR = 0.85, 95% CI = 0.52 to 1.38; P(trend) = .52). Our results suggest that vitamin B6 may be inversely associated with risk of colorectal neoplasia.

Specific cytogenetic abnormalities and k-ras mutation in two new human colorectal-adenoma-derived cell lines.

Two new human epithelial cell lines from sporadic colorectal adenomas designated S/RR and S/BR are reported. Both cell lines have extended growth capacities in vitro, reaching passages 38 and 40 respectively and show no sign of senescence. S/RR and S/BR cell lines have retained the ability to differentiate in vitro, as shown by mucin production from goblet-like cells. S/BR was derived from a large colonic tubular villous adenoma (3 to 4 cm), whereas S/RR was derived from a small rectal adenoma (< 1 cm), and may represent a relatively early-stage adenoma. The parent S/RR cell line has given rise to a clonogenic variant, designated S/RR/Cl, which also has shown no sign of senescence and has currently reached passage 43. Both the S/BR and the S/RR cell lines had mutations in codon 12 of the K-ras gene, while retaining one normal allele. The presence of this mutation, particularly in the cell line S/RR derived from a small adenoma, is consistent with ras mutation being a relatively early event in colorectal carcinogenesis and is perhaps involved in the ability of the adenoma cells to progress and to give rise to an immortal cell line in vitro. The clonal derivatives of the S/RR cells have an isochromosome 1q and abnormalities of chromosome 13 which include an isochromosome 13q. The S/BR cells have a deletion on the short arm of chromosome 1 and trisomy 7. The common abnormality for S/RR and S/BR cells involves chromosome 1. The involvement of different chromosomes in the 2 cell lines also suggests different pathways for malignant progression of the premalignant adenoma cells.

Genetic alterations during colorectal-tumor development.

Because most colorectal carcinomas appear to arise from adenomas, studies of different stages of colorectal neoplasia may shed light on the genetic alterations involved in tumor progression. We looked for four genetic alterations (ras-gene mutations and allelic deletions of chromosomes 5, 17, and 18) in 172 colorectal-tumor specimens representing various stages of neoplastic development. The specimens consisted of 40 predominantly early-stage adenomas from 7 patients with familial adenomatous polyposis, 40 adenomas (19 without associated foci of carcinoma and 21 with such foci) from 33 patients without familial polyposis, and 92 carcinomas resected from 89 patients. We found that ras-gene mutations occurred in 58 percent of adenomas larger than 1 cm and in 47 percent of carcinomas. However, ras mutations were found in only 9 percent of adenomas under 1 cm in size. Sequences on chromosome 5 that are linked to the gene for familial adenomatous polyposis were not lost in adenomas from the patients with polyposis but were lost in 29 to 35 percent of adenomas and carcinomas, respectively, from other patients. A specific region of chromosome 18 was deleted frequently in carcinomas (73 percent) and in advanced adenomas (47 percent) but only occasionally in earlier-stage adenomas (11 to 13 percent). Chromosome 17p sequences were usually lost only in carcinomas (75 percent). The four molecular alterations accumulated in a fashion that paralleled the clinical progression of tumors. These results are consistent with a model of colorectal tumorigenesis in which the steps required for the development of cancer often involve the mutational activation of an oncogene coupled with the loss of several genes that normally suppress tumorigenesis.