Patients with the hamartomatous polyposis Peutz-Jeghers and familial juvenile polyposis syndromes are predisposed to colorectal cancer but lack early genetic alterations found in adenomatous premalignant lesions. We studied hamartomatous polyps for the expression of an early preneoplastic colorectal neoplasia risk marker also found in familial adenomatous polyposis patients. Retrospective, genetic, and hospital archival tissue immunohistochemistry using Adnab-9, a premalignant marker often found in Paneth-like cells (PCs), was performed on sections of polyps from eight patients with Peutz-Jeghers syndrome, eight patients with familial juvenile polyposis, and 36 hyperplastic polyp control sections. Anti-α-defensin 5 (AD5), a universal PC marker, was also used to label a subgroup of sections. Hamartomatous polyposis patients also underwent specific genetic analysis. Eighty-nine percent of Peutz-Jeghers syndrome polyps labeled with Adnab-9 compared with 63% for AD5; 88% of familial juvenile polyposis sections also labeled with Adnab-9. Of the 36 hyperplastic polyp sections, only four (11%) labeled with Adnab-9 and one (3%) with AD5. Adnab-9 labeling of PCs in the epithelial elements of hamartomatous colonic lesions of hereditary hamartomatous syndrome patients reflects the predisposition to colorectal cancer, further justifying early intervention strategies.

BACKGROUND & AIMS:Preclinical studies in animal models, human epidemiological data, and clinical trials in patients with adenomatous polyposis have consistently indicated that sulindac and other nonsteroidal antiinflammatory drugs or cyclooxygenase inhibitors have the greatest potential efficacy among current candidates for colon tumor chemopreventive agents. However, at highly effective doses they all have some risk of toxicity, and their therapeutic profile might be improved by use at lower, more tolerable doses, in combination with a second agent acting via other mechanisms.METHODS:Sulindac was tested in combination with ursodeoxycholic acid (ursodiol), a naturally occurring 7-B-epimer of the bile component chenodeoxycholic acid, for prevention of adenomas in the Min mouse model of adenomatous polyposis.RESULTS:Ursodeoxycholic acid caused a dose-dependent decrease in the number of intestinal tumors. Unlike sulindac and other nonsteroidal anti-inflammatory drugs, which are quite beneficial in the distal intestine but are somewhat less effective in the proximal small intestine (especially the clinically important periampullary duodenum), ursodeoxycholate had equal efficacy throughout the entire intestine, both proximal and distal. Combined treatment with low-dose sulindac was less toxic, with normal weight gain and fewer gastrointestinal ulcerations than high-dose sulindac. Combined treatment with sulindac and ursodeoxycholate was more effective than either agent alone for the prevention of tumors throughout the entire intestine.CONCLUSIONS:These experiments provide the first evidence that ursodeoxycholic acid is effective for preventing adenomas in an animal model. Cyclooxygenase inhibition, when combined with this naturally occurring bile component, may become a promising approach for colon cancer prevention.

Background: Colonoscopy has become the method of choice for colorectal cancer screening. The use of colonoscopy for screening has created a significant problem with not enough physicians and endoscopy time to meet demand for population screening. Aim: To analyze the clinical utility and cost-effectiveness of a weekend clinic dedicated to performing screening colonoscopies. Methods: A weekend screening colonoscopy clinic was introduced in 1/02. Two physicians staffed the clinic twice per month on Saturday mornings (8 am - 12 noon). Data was obtained from each patient evaluated in the clinic from 1/02 to 5/03. The number of patient no shows and cancellations for each weekend clinic was calculated. A group of patients who had screening colonoscopies scheduled during the regular weekday served as controls. Patient demographics and colonoscopy findings were recorded. Cost-effectiveness was examined by determining the total cost of running the clinic and the reimbursement per week. Results: 277 colonoscopies were done in 23 weekend sessions over 16 months. Mean number of procedures completed per session was 11.9, mean number of procedures performed per physician was 5.9. The percent no shows/cancellations for the weekend clinics was significantly lower, 5.4%, compared to 14.4% for the weekday screening patients, p=0.0004. Gender: 55% F and 45% M. Mean age 56.1 years. Of the 277 colonoscopies performed during the weekend screening clinics, 118 (42.6%) were normal. Polyps were found in 87 (31.4%) patients: 42 patients with hyperplastic polyps, 45 (16.2%) patients with adenomas, 8 (2.9%) with advanced adenomas. Other findings included: carcinoid (1); granular cell tumor (1); diverticula or hemorrhoids only (58); AVMs (3), colitis (1), miscellaneous (5). No colon cancers were detected. 9/277 (3.2%) of colonoscopies were incomplete. Cost analysis showed that the total cost of operating the clinic per weekend shift was $2300.67 including opening the endoscopy suite with time and a half payment to staff of nurses, technicians, secretaries and scope washers. Revenue generated per weekend equaled $3,001.54 including procedure charge plus the recovery room charge at a mean 57% reimbursement rate. Conclusions: 1) A weekend screening colonoscopy clinic is an efficient way to perform a large number of procedures in a short period of time with high patient turn out. 2) Despite the costs involved in running a weekend clinic it is a profitable and cost-effective way to meet the increasingly high demand for screening colonoscopies.

Colorectal cancer remains one of the most common cancers, with more than 130,000 cases diagnosed annually in the United States (1). As a cause of cancer death, it is now second only to lung cancer. Although most colon cancer is sporadic, at least 15% of cases have some inherited component (2). Colon cancer is perhaps the most familial of all cancers. By age 70, the risk of colorectal cancer is only 2% in the low-risk general population, but increases to 8% for a person with one affected first-degree relative, and to 17% when two relatives first-degree relatives are affected (3). The risk increases further to about 60–80% for patients inheriting the genes that cause hereditary nonpolyposis colon cancer (4), and 95–100% for patients with untreated familial adenomatous polyposis (5). Awareness of genetic and other risk factors is important, because there are very effective means now available that could prevent most colon cancer morbidity and mortality.

Diffuse nodular lymphoid hyperplasia (DNLH) has long been recognized in the pediatric population and in adults with common variable immunodeficiency (CVID).1Louw JH Polypoid lesions of the large bowel in children with particular reference to benign lymphoid polyposis.J Pediatr Surg. 1968; 3: 195-208Abstract Full Text PDF PubMed Scopus (53) Google Scholar More recently, an association with HIV has been described.2Levendoglu H Rosen Y Nodular lymphoid hyperplasia of gut in HIV infection.Am J Gastroenterol. 1992; 87: 1200-1202PubMed Google Scholar Little is known about the prevalence, natural history, and clinical significance of DNLH in immunocompetent adults. DNLH is a rare lymphoproliferative disorder of unknown etiology. Typically, numerous polypoid nodules composed of hyperplastic benign lymphoid tissue are present in the small and/or large intestinal mucosa.3Rambaud JC De Saint-Louvent P Marti R Galian A Mason D Wassef M et al.Diffuse follicular lymphoid hyperplasia of the small intestine without primary immunoglobulin deficiency.Am J Med. 1982; 73: 125-132Abstract Full Text PDF PubMed Scopus (47) Google Scholar Although often an incidental finding, presentation is variable and depends on the size and extent of the nodules, as well as the presence or absence of underlying immunodeficiency. Treatment is directed at associated conditions because the disorder itself generally requires no intervention. Though considered benign by most investigators, several case reports document an association with malignant intestinal lymphoma.3Rambaud JC De Saint-Louvent P Marti R Galian A Mason D Wassef M et al.Diffuse follicular lymphoid hyperplasia of the small intestine without primary immunoglobulin deficiency.Am J Med. 1982; 73: 125-132Abstract Full Text PDF PubMed Scopus (47) Google Scholar, 4Castellano G Moreno D Galvao O Ballestín C Colina F Mollejo M et al.Malignant lymphoma of jejenum with common variable hypogammaglobulinemia and diffuse nodular hyperplasia of the small intestine.A case study and literature review. J Clin Gastroenterol. 1992; 15: 128-135Crossref PubMed Scopus (43) Google Scholar When DNLH is found predominantly in the colon, it can mimic a variety of polyposis syndromes but does not have the high risk of malignancy of familial adenomatous polyposis (FAP).5Burt RW Jacoby RF Polyposis syndromes.in: Yamada T Alpers DH Laine L Owyang C Powell DW Textbook of gastroenterology. 3rd ed. Lippincott Williams and Wilkins, Philadelphia1999: 1995-2022Google Scholar This underscores the importance of obtaining biopsy specimens for histopathologic diagnosis and the need for increased awareness of this poorly understood entity. A 24-year-old man presented with a 2-month history of hematochezia associated with intermittent lower abdominal pain relieved by defecation. There was no history of chronic diarrhea or recurrent sinopulmonary infections. He occasionally took non-steroidal anti-inflammatory drugs (NSAID) for musculoskeletal pain and had never received immunosuppressive medication. Family history was negative for inflammatory bowel disease, polyposis syndromes, and GI tract malignancies. Examination revealed obesity and a small reducible ventral hernia at the site of an incision for a Nissen fundoplication. Laboratory tests were remarkable for a normal complete blood count, erythrocyte sedimentation rate, lactate dehydrogenase, and quantitated immunoglobulins. At colonoscopy, there were innumerable sessile polyps (3–8 mm) extending from the rectum to the terminal ileum, with a short segment of sparing in the sigmoid colon (Fig. 1). These were less dense in the rectum, although the polyps there were larger and hyperemic with occasional superficial erosions. Capsule endoscopy demonstrated a few diminutive lymphoid nodules in the small bowel, with a distal predilection; the mucosa was intact without bleeding or stigmata of recent bleeding. Histopathologic evaluation of biopsy specimens from the colon and rectum revealed hypertrophic submucosal lymphoid follicles and prominent benign lymphoid aggregates in both the lamina propria and the submucosa (Fig. 2), without cellular atypia or increased mitotic activity. A diagnosis of DNLH was made. The above findings were compared with those at colonoscopy performed at another institution because of a positive test for fecal occult blood 16 months earlier. Of note, there was no significant change in the number, size, or distribution of polyps between the examinations. Likewise, the histopathologic findings were similar in biopsy specimens from both procedures. The cause of the hematochezia in the present case, although uncertain, was felt to be erosion of the larger, more distal colonic polyps. The patient was advised to limit the use of aspirin and NSAIDs, which he has done. At 8 months' follow-up, the patient was doing well and had not had clinically significant bleeding. The present case illustrates DNLH, a rare finding characterized by innumerable 3- to 6-mm sessile nodules throughout the colon and/or small intestine. Although various other conditions can have a similar gross appearance, DNLH is easily distinguished from other polyposis syndromes based on histopathologic features. As in the case described, lymphoid aggregates are morphologically normal, composed of a benign lymphocyte population confirmable by immunohistochemistry. For our patient, H&E stained paraffin sections of random colon and rectum biopsy specimens demonstrated colonic and rectal mucosa heavily infiltrated by lymphoid aggregates with prominent reactive secondary follicle formation, confirmed by immunohistochemistry for CD3 and CD20. Cyclin D1 expression was negative by immunohistochemistry, thus excluding a diagnosis of intestinal mantle cell lymphoma or multiple lymphomatous polyposis. Numerous polypoid growths containing hyperplastic lymphoid tissue along the GI tract have been described previously. First termed “gastrointestinal pseudoleukemia,” the finding has since been referred to in published reports by a variety of names, thereby contributing to the confusion surrounding it. Although the term DNLH or, more simply, nodular lymphoid hyperplasia generally is used to describe the condition in children and those with concomitant CVID, benign lymphoid polyposis has been favored in surgical publications, particularly for cases with prominent colonic involvement.6Benchimol D Frileux P Herve de Sigalony JP Pare R Benign lymphoid polyposis of the colon.Report of a case in an adult. Int J Colorect Dis. 1991; 6: 165-168Crossref PubMed Scopus (7) Google Scholar Others refer to the condition as colonic lymphoid hyperplasia, colonic lymphoid nodules, and benign lymphomatosis.7Bharadhwaj G Triadafilopoulos G Endoscopic appearances of colonic lymphoid nodules: new faces of an old histopathological entity.Am J Gastroenterol. 1995; 90: 946-950PubMed Google Scholar Further clouding matters is the use of similar terms for GI tract lymphoma, including diffuse lymphomatous polyposis and multiple lymphomatous polyposis.8Vignote ML Chicano M Rodríguez FJ Acosta A Gómez F Poyato A et al.Multiple lymphomatous polyposis of the GI tract: report of a case and review.Gastrointest Endosc. 2002; 56: 579-582Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar Assessing the true prevalence of DNLH of the colon in adults is challenging. Because large colonoscopic series are lacking, retrospective studies based on barium contrast radiography have been cited from radiology publications to estimate its prevalence in the general population.9Kenney PJ Koehler RE Shackelford GD The clinical significance of large lymphoid follicles of the colon.Radiology. 1982; 142: 41-46PubMed Google Scholar However, these studies pertain to the frequency of small lymphoid follicles (3 mm or less in diameter) in the colons of adults and not polypoid lymphoid nodules, which are typically 3 to 6 mm or more in diameter.5Burt RW Jacoby RF Polyposis syndromes.in: Yamada T Alpers DH Laine L Owyang C Powell DW Textbook of gastroenterology. 3rd ed. Lippincott Williams and Wilkins, Philadelphia1999: 1995-2022Google Scholar An autopsy series claimed an average macroscopic density of 18 lymphoid follicles/cm2 of normal adult colon, although how this translates to clinically detectable lesions is unclear.10Langman JM Rowland R The number and distribution of lymphoid follicles in the human large intestine.J Anat. 1986; 194: 189-194Google Scholar Bharadhwaj and Triadafilopoulos7Bharadhwaj G Triadafilopoulos G Endoscopic appearances of colonic lymphoid nodules: new faces of an old histopathological entity.Am J Gastroenterol. 1995; 90: 946-950PubMed Google Scholar found a 1.9% frequency for endoscopically recognizable colonic lymphoid nodules in 696 consecutive colonoscopies performed for a variety of indications. Of the cases with colonic lymphoid nodules, only 3 were consistent with traditionally described polypoid-appearing nodular lymphoid hyperplasia, thus lowering the frequency to 0.43%. Our review of published articles referring to adults found only 3 cases of DNLH of the colon; Benchimol et al.6Benchimol D Frileux P Herve de Sigalony JP Pare R Benign lymphoid polyposis of the colon.Report of a case in an adult. Int J Colorect Dis. 1991; 6: 165-168Crossref PubMed Scopus (7) Google Scholar speculated that there were at least two others.11Sher MH Tedeschi LG Lymphoid polyposis of the colon.Ann Surg. 1972; 38: 322-327Google Scholar, 12Colarian J Calzada R Jaszewski R Nodular lymphoid hyperplasia of the colon in adults: is it common?.Gastrointest Endosc. 1990; 36: 421-422Abstract Full Text PDF PubMed Scopus (9) Google Scholar The majority of patients with endoscopically detectable DNLH are asymptomatic.4Castellano G Moreno D Galvao O Ballestín C Colina F Mollejo M et al.Malignant lymphoma of jejenum with common variable hypogammaglobulinemia and diffuse nodular hyperplasia of the small intestine.A case study and literature review. J Clin Gastroenterol. 1992; 15: 128-135Crossref PubMed Scopus (43) Google Scholar, 5Burt RW Jacoby RF Polyposis syndromes.in: Yamada T Alpers DH Laine L Owyang C Powell DW Textbook of gastroenterology. 3rd ed. Lippincott Williams and Wilkins, Philadelphia1999: 1995-2022Google Scholar As the size of the polypoid nodules increases, so does the frequency of symptoms, which include diffuse abdominal pain, intussusception, and hemorrhage. Approximately 20% of patients with CVID will have concomitant DNLH, which often presents as chronic diarrhea with or without malabsorption, Giardia infection, and/or protein-losing enteropathy. DNLH also has been found incidentally in patients with FAP, HIV, or IgA deficiency.2Levendoglu H Rosen Y Nodular lymphoid hyperplasia of gut in HIV infection.Am J Gastroenterol. 1992; 87: 1200-1202PubMed Google Scholar, 3Rambaud JC De Saint-Louvent P Marti R Galian A Mason D Wassef M et al.Diffuse follicular lymphoid hyperplasia of the small intestine without primary immunoglobulin deficiency.Am J Med. 1982; 73: 125-132Abstract Full Text PDF PubMed Scopus (47) Google Scholar DNLH is part of a spectrum of benign lymphoproliferative disorders of the GI tract. Lymphoid hyperplasia is defined by an increase in the number and/or size of lymphoid follicles, such that lymphoid tissue is discernible on gross inspection.13Fenoglio-Preiser C Noffsinger AE Stemmermann GN Lantz PE Listrom MB Rilke FO Gastrointestinal hematologic lesions. 2nd ed. Gastrointestinal pathology; an atlas and text. Lippincott Williams and Wilkins, Philadelphia1997: 1129-1167Google Scholar The term lymphoid follicular pattern has been used to describe the presence of multiple, 1- to 3-mm uniform nodular filling defects seen commonly in children, and in up to 13% of adults.9Kenney PJ Koehler RE Shackelford GD The clinical significance of large lymphoid follicles of the colon.Radiology. 1982; 142: 41-46PubMed Google Scholar Lesions 2 mm or less in diameter are considered normal in the pediatric population.9Kenney PJ Koehler RE Shackelford GD The clinical significance of large lymphoid follicles of the colon.Radiology. 1982; 142: 41-46PubMed Google Scholar Focal nodular hyperplasia can be seen in the stomach surrounding peptic ulcers and often in the terminal ileum of children and young adults. When the large intestine is involved, there is a predilection for the rectum. Nodules are typically 2 to 4 mm in diameter, with vascular congestion and wall edema seen histologically.13Fenoglio-Preiser C Noffsinger AE Stemmermann GN Lantz PE Listrom MB Rilke FO Gastrointestinal hematologic lesions. 2nd ed. Gastrointestinal pathology; an atlas and text. Lippincott Williams and Wilkins, Philadelphia1997: 1129-1167Google Scholar In DNLH, numerous polypoid growths stud a large extent of the small and/or large intestine. Although typically 3 to 6 mm in diameter with normal overlying mucosa, they can increase in size to larger than 1 cm.5Burt RW Jacoby RF Polyposis syndromes.in: Yamada T Alpers DH Laine L Owyang C Powell DW Textbook of gastroenterology. 3rd ed. Lippincott Williams and Wilkins, Philadelphia1999: 1995-2022Google Scholar When DNLH is found in the colon, the endoscopic appearance can be strikingly similar to that of polyposis syndromes, including FAP, multiple lymphomatous polyposis, juvenile or hamartomatous polyposis, and hyperplastic polyposis, among others. Microscopically, the nodules are composed of grouped hypertrophic lymphoid follicles with enlarged germinal centers and an intact mantle zone. They may occupy both the lamina propria and the superficial submucosa.3Rambaud JC De Saint-Louvent P Marti R Galian A Mason D Wassef M et al.Diffuse follicular lymphoid hyperplasia of the small intestine without primary immunoglobulin deficiency.Am J Med. 1982; 73: 125-132Abstract Full Text PDF PubMed Scopus (47) Google Scholar, 6Benchimol D Frileux P Herve de Sigalony JP Pare R Benign lymphoid polyposis of the colon.Report of a case in an adult. Int J Colorect Dis. 1991; 6: 165-168Crossref PubMed Scopus (7) Google Scholar, 13Fenoglio-Preiser C Noffsinger AE Stemmermann GN Lantz PE Listrom MB Rilke FO Gastrointestinal hematologic lesions. 2nd ed. Gastrointestinal pathology; an atlas and text. Lippincott Williams and Wilkins, Philadelphia1997: 1129-1167Google Scholar Although DNLH in CVID is felt to be secondary to a block in B-cell maturation, its pathogenesis in immunocompetent individuals is speculative.3Rambaud JC De Saint-Louvent P Marti R Galian A Mason D Wassef M et al.Diffuse follicular lymphoid hyperplasia of the small intestine without primary immunoglobulin deficiency.Am J Med. 1982; 73: 125-132Abstract Full Text PDF PubMed Scopus (47) Google Scholar, 6Benchimol D Frileux P Herve de Sigalony JP Pare R Benign lymphoid polyposis of the colon.Report of a case in an adult. Int J Colorect Dis. 1991; 6: 165-168Crossref PubMed Scopus (7) Google Scholar A frequently proposed hypothesis implicates an intestinal antigenic stimulus, possibly infectious, that leads to repetitive stimulation and eventual hyperplasia of lymphoid follicles.3Rambaud JC De Saint-Louvent P Marti R Galian A Mason D Wassef M et al.Diffuse follicular lymphoid hyperplasia of the small intestine without primary immunoglobulin deficiency.Am J Med. 1982; 73: 125-132Abstract Full Text PDF PubMed Scopus (47) Google Scholar A selective GI tract immunodeficiency also has been postulated.5Burt RW Jacoby RF Polyposis syndromes.in: Yamada T Alpers DH Laine L Owyang C Powell DW Textbook of gastroenterology. 3rd ed. Lippincott Williams and Wilkins, Philadelphia1999: 1995-2022Google Scholar The long-term prognosis of patients with DNLH has not been clearly established, although most authorities believe the course to be benign. Nodules in affected children often regress with age, but there are sporadic reports of the development of small intestinal non-Hodgkin's lymphoma in both CVID and immunocompetent patients.3Rambaud JC De Saint-Louvent P Marti R Galian A Mason D Wassef M et al.Diffuse follicular lymphoid hyperplasia of the small intestine without primary immunoglobulin deficiency.Am J Med. 1982; 73: 125-132Abstract Full Text PDF PubMed Scopus (47) Google Scholar, 4Castellano G Moreno D Galvao O Ballestín C Colina F Mollejo M et al.Malignant lymphoma of jejenum with common variable hypogammaglobulinemia and diffuse nodular hyperplasia of the small intestine.A case study and literature review. J Clin Gastroenterol. 1992; 15: 128-135Crossref PubMed Scopus (43) Google Scholar Based on the light microscopy finding of atypical cell populations within hyperplastic lymphoid nodules, Castellano et al.4Castellano G Moreno D Galvao O Ballestín C Colina F Mollejo M et al.Malignant lymphoma of jejenum with common variable hypogammaglobulinemia and diffuse nodular hyperplasia of the small intestine.A case study and literature review. J Clin Gastroenterol. 1992; 15: 128-135Crossref PubMed Scopus (43) Google Scholar suggested a transition between DNLH and lymphoma, but, without molecular evidence for any genetic changes correlating with such a proposed progression, this remains controversial. To our knowledge, there are no reports of progression of DNLH to intestinal lymphoma in an adult. A study from Japan and Sweden suggests an association between colonic lymphoid nodules and non-protruding colorectal neoplasia (adenomas and early carcinomas), further challenging the view that DNLH is a benign disorder.14Rubio CA Nonprotruding colorectal neoplasms: epidemiologic viewpoint.World J Surg. 2000; 24: 1098-1103Crossref PubMed Scopus (16) Google Scholar Moreover, colon carcinogenesis experiments in rats show that colon carcinomas occur more often near lymphoid nodules.15LaMont JT O'Gorman TA Experimental colon cancer.Gastroenterology. 1978; 75: 1157-1169PubMed Google Scholar However, there is no recommendation for surveillance in patients with any form of DNLH. Likewise, no specific therapy is indicated, despite the use of corticosteroids, radiotherapy, and polypectomy in the past.1Louw JH Polypoid lesions of the large bowel in children with particular reference to benign lymphoid polyposis.J Pediatr Surg. 1968; 3: 195-208Abstract Full Text PDF PubMed Scopus (53) Google Scholar, 12Colarian J Calzada R Jaszewski R Nodular lymphoid hyperplasia of the colon in adults: is it common?.Gastrointest Endosc. 1990; 36: 421-422Abstract Full Text PDF PubMed Scopus (9) Google Scholar Some lymphoid tissue is detectable grossly in a large percentage of the pediatric population and often in adults, both in the small and large intestine. This is in stark contrast to the more rare condition, DNLH, in which hyperplastic follicles form polypoid nodules that carpet variable portions of the GI tract. Even more uncommon is DNLH of the colon in an adult, a disorder that must be distinguished from a variety of polyposis syndromes to avoid misdiagnosis and unnecessary radical treatments.

DNA mismatch repair is important because of its role in maintaining genomic integrity and its association with hereditary non-polyposis colon cancer (HNPCC). To identify new human mismatch repair proteins, we probed nuclear extracts with the conserved carboxy-terminal MLH1 interaction domain. Here we describe the cloning and complete genomic sequence of MLH3, which encodes a new DNA mismatch repair protein that interacts with MLH1. MLH3 is more similar to mismatch repair proteins from yeast, plants, worms and bacteria than to any known mammalian protein, suggesting that its conserved sequence may confer unique functions in mice and humans. Cells in culture stably expressing a dominant-negative MLH3 protein exhibit microsatellite instability. Mlh3 is highly expressed in gastrointestinal epithelium and physically maps to the mouse complex trait locus colon cancer susceptibility I (Ccs1). Although we were unable to identify a mutation in the protein-coding region of Mlh3 in the susceptible mouse strain, colon tumours from congenic Ccs1 mice exhibit microsatellite instability. Functional redundancy among Mlh3, Pms1 and Pms2 may explain why neither Pms1 nor Pms2 mutant mice develop colon cancer, and why PMS1 and PMS2 mutations are only rarely found in HNPCC families.

Genetic knockout or pharmacological inhibition of cyclooxygenase-2 decreases the number and size of adenomas in mouse models of familial adenomatous polyposis. Epidemiological and clinical studies in humans indicate that the entire class of nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit both COX-1 and COX-2 enzymes are promising colon cancer chemopreventive agents. We used the Apc mutant Min mouse model to test combinations of agents that might maximize preventive benefit with minimal toxicity because they act via different mechanisms. Min mice (n = 144) were exposed to low doses of the nonselective COX inhibitor piroxicam and the ornithine decarboxylase (ODC) inhibitor difluoromethylornithine (DFMO), beginning at the time they were weaned and continuing throughout the duration of the experiment. Piroxicam at 12, 25, and 50 ppm in the diet caused dose-dependent decreases in the number of tumors in the middle and distal portions of the small intestine. This decrease in tumor multiplicity was associated with a striking decrease in the size of those tumors that did grow out. In contrast, none of the doses of piroxicam alone decreased tumor multiplicity in the proximal portion of the intestine (duodenum). Exposure to DFMO (0.5 or 1.0% in water) caused a dose-dependent decrease in tumor multiplicity in the middle and distal portions of the small intestine. However, this decreased multiplicity was not associated with a striking decrease in the size of the tumors. Combined treatment of mice with piroxicam plus DFMO was much more effective than either agent alone and resulted in a significant number of mice totally free of any intestinal adenomas (P < 0.001), in contrast to the 100% incidence and high multiplicity in control Min mice. In addition to this profound effectiveness in reducing tumor number, the few residual tumors in mice treated with the combined drugs were markedly smaller in size than tumors that arose from control Min mice. These experiments suggest that selective COX-2 inhibition combined with ODC inhibition is a very promising approach for colon cancer prevention. These COX-2 and ODC inhibitor drugs were not overtly toxic at the doses used when administered to mice after weaning. However, when treatment was begun in utero, the Mendelian expected progeny ratio of 1:1 that we routinely obtained in untreated control litters was no longer observed. Apc(min)/+ progeny of pregnant dams treated with piroxicam and/or DFMO were reduced in number and their ratio to Apc+/+ progeny was decreased to approximately 0.28:1. Thus, these agents are effective against adenomas that have homozygous mutation of the APC gene and also select against fetuses bearing a heterozygous mutation in the APC gene.

The interaction between mutations in the tumor-suppressor genes Apc and p53 was studied in congenic mouse strains to minimize the influence of polymorphic modifiers. The multiplicity and invasiveness of intestinal adenomas of Apc(Min/+) (Min) mice was enhanced by deficiency for p53. In addition, the occurrence of desmoid fibromas was strongly enhanced by p53 deficiency. The genetic modifier Mom1 and the pharmacological agents piroxicam and difluoromethylornithine each reduced intestinal adenoma multiplicity in the absence of p53 function. Mom1 showed no influence on the development of desmoid fibromas, whereas the combination of piroxicam and difluoromethylornithine exerted a moderate effect. The ensemble of tumor suppressors and modifiers of a neoplastic process can be usefully analyzed in respect to tissue specificity and synergy.

Epidemiological and animal studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) may reduce colon cancer risk. NSAIDs nonselectively inhibit both the constitutive cyclooxygenase (COX) 1 associated with side effects and the desired therapeutic target COX-2, which is induced in inflammation and neoplasia. We used the adenomatous polyposis coli (Apc) mutant Min mouse model to determine whether the selective COX-2 inhibitor celecoxib is effective for adenoma prevention and/or regression, and whether it might be safer than the nonselective NSAID previously shown to be most effective in this model, piroxicam. Min mice (n = 120) were randomized to treatment with celecoxib (0, 150, 500, or 1500 ppm celecoxib mixed in the diet) or piroxicam. To distinguish prevention from regression effects, groups were treated either "early" (before adenomas develop) or "late" (after most adenomas are established). Celecoxib caused dramatic reductions in both the multiplicity and size of tumors in a dose-dependent manner (P < 0.01). Early treatment with 1500 ppm of celecoxib was effective for prevention, decreasing tumor multiplicity to 29% and tumor size to only 17% of controls (P < 0.01). Late treatment demonstrated regression effects, reducing tumor multiplicity and size by about half. In contrast to the significant toxicity of piroxicam, which caused ulcers complicated by perforation and bleeding, celecoxib caused no gastrointestinal side effects and did not inhibit platelet thromboxane B2 at plasma drug levels similar to those obtained in early clinical trials in humans. These results provide the first evidence that selective inhibitors of COX-2 are safe and effective for the prevention and regression of adenomas in a mouse model of adenomatous polyposis and strongly support ongoing clinical trials in humans with the same syndrome. The broader population of patients with common sporadic adenomas that have somatic mutations of the same gene (APC) may also benefit from this treatment approach.