Randomized comparison of surveillance intervals after colonoscopic removal of newly diagnosed adenomatous polyps. The National Polyp Study Workgroup

Basis and consequences of primary and secondary prevention of gastrointestinal tumors

Carcinomas of the gastrointestinal tract (GI) are among the most common malignancies with regard to their incidence and mortality. Nutritional factors play an important role in the tumor development. The strength of their influence varies with the localization in the GI tract. Epidemiological studies focusing on GI cancer incidence or mortality as an endpoint necessitate large numbers of subjects to achieve significant results. Generally, a low energy and fat intake and a high intake of antioxidative vitamins (vitamin C, E, beta-carotene) and secondary plant metabolites (especially polyphenols) appear to be protective in GI carcinogenesis. Moderate drinking of alcohol and increased consumption of whole grain products, as opposed to highly refined carbohydrates, may help to reduce the risk of colon cancer. The recommended type of diet is low in fat, especially in saturated fatty acids, includes monounsaturated fatty acids, and includes moderate amounts of polyunsaturated fatty acids (no more than 10% of calories). Moderate consumption of salt and of highly salted, smoked, and barbecued foods should be encouraged. Obesity should be avoided by trying to match energy intake with expenditure while increasing physical activity levels. The mechanisms by which nutritional factors act especially on molecular events still remain to be examined. The use of molecular biomarkers will help us better understand cancer development as well as the role and significance of nutritional factors in this process.

The difference in colon polyp size before and after removal

BACKGROUND

Accurate knowledge of polyp size is important in assessing cancer risk in both clinical studies and individual patients. We sought to determine if a difference exists between the endoscopic estimation of colon polyp size and the actual measurement after removal.

METHODS

We measured polyps in a systematic fashion. Using open biopsy forceps as a guide, the largest diameter of 31 pedunculated polyps was estimated endoscopically. The polyp was then removed by snare polypectomy and directly measured by a technician who was blinded to the endoscopic estimate. Each polyp was also measured after formalin fixation by a pathologist who was blinded to previous measurements.

RESULTS

There was a significant difference between the endoscopic estimates and the postpolypectomy measurements. Endoscopic estimates on average were 1.6 mm greater than the postpolypectomy measurements (p< 0.05), representing an 18% difference. Twenty-three of the 31 (74%) endoscopic estimates were larger than the postpolypectomy measurements. There was not a significant difference between the postpolypectomy and postfixation measurements.

CONCLUSIONS

The size of polyps measured endoscopically is significantly larger on average than postpolypectomy measurements. This is most likely due to factors involved in the removal of the in vivo polyp.

Establishment of a colonic polyp registry in Rhode Island

A colonic adenomatous polyp registry (PR) has been organized at the Roger Williams Medical Center whose main functions are to prevent the occurrence of colorectal cancer (CRC) in the enrollees, to provide a population of subjects for epidemiological and interventional studies, and to provide educational, including dietary, information to subjects and physicians. One hundred four and 202 patients with polyps, originally retrieved from the hospital pathology files, were enrolled in the 1984 and 1987 cohorts, respectively, of whom about 90% were followed for at least three years after polypectomy. Three carcinomas, all Dukes A, were found in the right colon in the follow-up period. New polyps identified in the first three years after polypectomy were generally small tubular adenomas with a greater predilection for the right colon than was found for the index polyps. Risk factors for new polyps included history of previous polyps and, probably, multiple index polyps. The use of colonoscopy for postpolypectomy surveillance increased between 1984 and 1987. About 25% of the subjects in each cohort were either lost to follow-up or received no endoscopic surveillance. On the other hand, some of those who were followed were probably subjected to excessive numbers of procedures. Defects in the PR include inadequacy of personal and family history data, and steady loss of patients during the three to six years after polypectomy. Despite the small size and limited resources of our hospital, its colonic polyp registry has already provided information that may help in the management of patients with this premalignant condition. The more widespread use of securely funded polyp registries would probably reduce the incidence of metachronous CRC in that population and would have significant epidemiological and educational functions.

Cost-effectiveness model for colon cancer screening

BACKGROUND & AIMS

The relative efficacy and effectiveness of different colon screening programs has not been assessed. The purpose of this analysis was to provide a model for comparing several colon screening programs and to determine the key variables that impact program effectiveness.

METHODS

Five screening programs were compared: annual fecal occult blood test (FOBT) alone, flexible sigmoidoscopy, flexible sigmoidoscopy and FOBT combined, one-time colonoscopy, and air-contrast barium enema. Key variables were adjusted for sensitivity analyses. Cost-effectiveness was defined as the cost per cancer death prevented.

RESULTS

FOBT alone prevents fewer cancer deaths than the other programs. The addition of flexible sigmoidoscopy to the FOBT increases the rate of cancer prevention. One-time colonoscopy has the greatest impact on colorectal cancer mortality, largely because of assumptions that cancer would be prevented in most patients who undergo polypectomy. FOBT alone is the most cost-effective of the programs, but the cost is sensitive to several key variables.

CONCLUSIONS

The model shows key variables that impact the cost-effectiveness of colon screening programs. Compliance is an important determinant of effectiveness of all of the screening programs. Future study should be focused on methods of patient education that improve patient compliance with screening.

Hereditary nonpolyposis colorectal cancer and colonic adenomas: aggressive adenomas?

Hereditary nonpolyposis colorectal cancer (HNPCC) results from an inherited defect in one of the genes responsible for repair of errors that occur during DNA replication. Affected individuals have high risk for cancers of the colon and certain extracolonic sites. It appears that HNPCC patients form adenomas at about the same rate s the general population and there is some circumstantial evidence that adenoma is the precursor to colorectal carcinoma in the syndrome. It is hypothesized that HNPCC features accelerated progression from colonic adenoma to carcinoma, a process theoretically driven by the inability to repair DNA mismatches. Evidence in support of the "Aggressive Adenoma" in HNPCC is provided. We discuss our recommendations for colonoscopic surveillance on an annual basis for HNPCC gene-positive individuals, and for genetic counseling.

Colonoscopic polypectomy: indication, technique, and therapeutic implications

The flexible fibroscopic colonoscope has changed the way we approach colonic disease. The technique of safe, effective colonoscopy is discussed including the indications and contraindications for therapeutic intervention via the colonoscope. The techniques of polypectomy is described, including some tips for methodology gained by the broad experience of the author, and admonition against the possible complications which can be life-threatening. The application for polypectomy in the presence of in-situ or invasive cancer is presented. The possible future development of colonoscopic and laparoscopic techniques are presented. The article concludes with a discussion of the monumental work of the National Polyp Study documenting that patients undergoing polypectomy have a significant reduction in the incidence of colon cancer. Application of the knowledge to the general population requires the identification of at-risk populations.

Flat neoplastic lesions of the colon and rectum detected by high-resolution video endoscopy and chromoscopy

Because small flat colorectal neoplastic lesions (i.e., flat adenomas and flat adenocarcinomas) may be as translucent as the surrounding mucosa, they can remain undetected at conventional endoscopy. By combining high-resolution video endoscopy and chromoscopy, we detected 109 colorectal flat neoplastic lesions in 55 of 232 patients studied. Forty-three (78%) of the 55 patients with flat neoplastic lesions were over 60 years of age. No flat neoplastic lesions were seen in patients under 40 years of age. Flat neoplastic lesions were more frequent in men (35%) than in women (15%). Seventy-seven (71%) of the 109 flat neoplastic lesions measured 0.5 cm or less, 23 (21%) between 0.6 and 1.0 cm, and 9 (8%) more than 1.0 cm. Low-grade dysplasia and high-grade dysplasia were found in 94 (86%) and 13 (12%) of the flat neoplastic lesions, respectively. Adenocarcinoma was diagnosed in 3 (3%) flat lesions: 1 (1%) carcinoma originating in a flat adenoma and 2 (2%) adenocarcinomas without recognizable adenomatous elements. No adenocarcinomas were seen in lesions measuring 1.0 cm or less. Fourteen flat neoplastic lesions had a central depression at endoscopy. Flat neoplastic lesions with central depression more frequently showed high-grade dysplasia (43%) than did flat neoplastic lesions without central depression (7%). Central depression in flat neoplastic lesions should be considered a possible endoscopic marker for severe dysplasia. Our results suggest that flat neoplastic lesions occur more frequently than previously reported in Scandinavia. Flat adenomas may play an important role in the histogenesis of colorectal cancer.

A randomized surveillance study of patients with pedunculated and small sessile tubular and tubulovillous adenomas. The Funen Adenoma Follow-up Study

BACKGROUND

We wanted to assess the influence of various surveillance intervals on the risk of new neoplasia after removal of pedunculated and small sessile tubular and tubulovillous adenomas.

METHODS

After initial colonoscopic polypectomy patients were randomized to surveillance with either 2 years (group A) or 4 years (group B) between colorectal examinations.

RESULTS

The cumulated risk of a patient having new adenomas was 35.0% (28.7-41.4%) in group A and 35.5% (28.4-42.7%) in group B after 48 months. The risk increased to 44.9% (36.0-53.9%) and 60.1% (48.5-71.7%), respectively, after 96 months. The risk of significant neoplasia (carcinoma or adenoma with villous structure, severe dysplasia, or diameter > 10 mm) was 5.2% (2.3-8.1%) and 8.6% (3.8-13.3%) after 48 months and 8.6% (4.2-13.0%) and 17.4% (7.6-27.2%) after 96 months. More than one adenoma at first examination was associated with higher risk of new adenomas. Furthermore, we found a tendency for age above 60 years and male gender to be associated with higher risk of new adenomas. More than two adenomas at first examination was the only factor found to be associated with a higher risk of new significant neoplasia. One patient in group A and two patients in group B developed cancer, which is not significantly different from the number expected (3.43) in the average Danish population (RR = 0.9, 0.2-2.6).

CONCLUSION

After colonoscopy with removal of all polyps, colorectal examination at 4 years resulted in a similar risk of new adenomas compared with examinations at 2 and 4 years. However, new significant neoplasia tended to be more frequent when first surveillance was at 4 years. Extending the surveillance to 8 years also tended to increase the risk more in the group being examined every 4 years, but reduction of the number of surveillance examinations by more than 50% and a probable reduction of complications from surveillance examinations themselves may justify a recommendation for the longest interval.

Hereditary nonpolyposis colorectal cancer: results of long-term surveillance in 50 families

A surveillance programme comprising either colonoscopy of sigmoidoscopy plus barium enema every 2-3 years was instituted in 50 hereditary nonpolyposis colorectal cancer (HNPCC) families. The families included 238 patients with colorectal cancer (CRC) (mean age at diagnosis: 43.7 years; range: 16-86 years). These patients had 597 first-degree relatives of whom 493 could be traced and 388 (79%) accepted the invitation for screening. The control group were relatives (index patients) with symptomatic CRC. The average follow-up duration was 5 years (1-20 years). Screening led to the detection of adenomas in 33 patients and CRC in 11 patients. Pathological examination revealed 1 Dukes' A, 7 Dukes' B and 3 Dukes' C cancers. In contrast, among the control group 47% had advanced CRC (Dukes' C or distant metastases). The 5-year survival of the screen-detected cases was 87% versus 63% in the control group. Of the 11 CRC cases in the screening group, 4 were detected within 1-4 years after a negative colonic examination. A large proportion of the polyps found in the screening and control groups showed a villous growth pattern and/or a high degree of dysplasia. We conclude that periodic examination of HNPCC families allows the detection of cancer at an earlier stage than in patients not under surveillance. Because of the possibly more aggressive nature of polyps associated with HNPCC, we recommend a screening interval of 1-2 years.

Follow-up after polypectomy: consensus?

Patients who have had a colorectal adenoma resected have an increased risk of subsequent cancer and may benefit from follow-up surveillance. Surveillance strategies should be tailored to the assessed risk of each individual patient. A number of long-term follow-up studies indicate that the risk of metachronous neoplasia is higher if on index colonoscopy there were multiple (> or = 2) adenomas, or if any adenoma was large (> or = 1 cm), contained villous tissue or severe dysplasia, or if the patient had a family history of colorectal neoplasia. Data from the U.S. National Polyp Study indicate that polyp resection and follow-up surveillance greatly reduces the incidence of metachronous cancer, and that the first follow-up colonoscopy does not need to be performed for 3 years. Current data have been incorporated into a comprehensive consensus practice guideline.

Prospects for the secondary prevention of colorectal cancer: screening by flexible sigmoidoscopy?

It may be useful to draw an analogy between the proposed screening programme for colorectal cancer and the cervical cancer screening programme. Both tumours show a spectrum of histological abnormalities consistent with a premalignant phase. The natural history of these premalignant lesions is poorly understood and although some will progress, if untreated, to invasive disease, most will not. Light microscopy cannot confidently distinguish which cases will progress and which will regress, and clinicians are therefore obliged to treat all. This will result in the destruction of many lesions of uncertain malignant potential. The secondary prevention of cervical cancer, although therapeutically efficacious, is inefficient. A lack of understanding of the natural history of intraepithelial neoplasia has frustrated attempts to develop rational referral criteria, and it is only now that the appropriate trials are being undertaken. The development of outpatient investigative and therapeutic procedures has resulted in many more women being referred for investigation and treatment, with predictable pressure on other services offered by gynaecologists, but no demonstrable saving of life. Similar uncertainties surround a screening programme for colorectal cancer. The principal concerns are not about the efficacy of polypectomy in interrupting the polyp cancer sequence, although uncertainties about the frequency with which cancer arises de novo do require that the effectiveness of this intervention is formally tested. Our major concerns are with compliance, and the management of the individual who tests positive--that is, who is found to have a distal polyp. Technological advances and operator enthusiasm may, as has happened with the cervical screening programme, lead to a relaxation in the indications for further investigation and treatment. Such a development would affect resources substantially if a population screening programme were in place. Nevertheless, there are grounds for believing that a screening programme for colorectal cancer, using sigmoidoscopy, might be successful in certain age groups if compliance was satisfactory. The scale of benefits may be comparable with those achieved by the breast screening programme. Our limited cost analysis, which relates to only to specific items of clinical activity, suggest that the mean cost for each case of cancer prevented will be about 8000 pounds sterling. These conclusions suggest that screening by flexible sigmoidoscopy merits serious consideration. It is also imperative, however, that consideration should be given to resolving some of the uncertainties about the clinical management and surveillance of those found to have distal polyps.

Screening for colorectal cancer

In the past few years, knowledge of the clinical, biologic, and molecular genetic characteristics of colorectal cancer has greatly increased. Although the most cost-effective approach remains to be identified, screening for colorectal cancer can decrease mortality due to this disease by detecting cancers at earlier stages and allowing the removal of adenomas, thus preventing the subsequent development of cancer. Molecular studies that have helped define the genetic basis for this disease hold great promise for the development of better and more powerful methods to identify populations at risk. Individually, these technological, clinical, and basic-science advances are exciting; together, they promise to move us closer to the goal of substantially reducing mortality due to colorectal cancer.

Faecal occult blood testing and colonoscopy in the surveillance of subjects at high risk of colorectal neoplasia

Colonoscopy is the established method of surveillance of subjects at high risk of developing colorectal neoplasia but the procedure is expensive, time consuming and occasionally hazardous. Faecal occult blood tests can be prepared at home and are cheap, simple and safe. Hemeselect is an immunological faecal occult blood test that is more sensitive for colorectal cancer than Haemoccult. The aim of this study was to determine the sensitivity of the Hemeselect test for asymptomatic colorectal neoplasia in subjects at high risk of the disease who were undergoing colonoscopy, thus assessing its suitability as an alternative means of screening high-risk groups. A total of 919 asymptomatic subjects were asked to complete Hemeselect tests. These were completed satisfactorily by 808 individuals (compliance rate 88 per cent) and were positive in 164 patients (20 per cent). At colonoscopy 11 cancers were detected in ten patients (seven Hemeselect positive) and 36 (16 Hemeselect positive) had at least one adenoma 1 cm or more in diameter. The test sensitivites of Hemeselect for carcinoma and large (1 cm or more) adenomas were 70 and 44 per cent respectively. In a subset of 417 subjects who also completed Haemoccult tests, the sensitivities were 33 and 18 per cent. Hemeselect specificity is 88 per cent compared with 98 per cent for Haemoccult. While the sensitivity of Hemeselect is higher than that of Haemoccult, it is still insufficient to replace colonoscopy in high-risk groups.

Suggested screening guidelines for familial colorectal cancer

Guidelines for screening for colorectal cancer in subjects with a positive family history of the disease, without the use of DNA based screening, are outlined. These suggestions are derived from (a) the experience of screening 644 subjects at an estimated lifetime risk of dying from colorectal cancer of 10% or more, in the St Mark's Family Cancer Clinic, over six years, and (b) a review of published studies, particularly incorporating the experience of the International Collaboration Group on Hereditary Non-polyposis Colorectal Cancer (HNPCC). Selection of subjects for surveillance depends upon the empirical evaluation of their risk of colorectal cancer, based upon family history details, with the exclusion of a diagnosis of familial adenomatous polyposis in the family. When DNA predictive tests for genes predisposing to HNPCC are available, surveillance can be directed at subjects with a germline mutation known to confer an increased genetic risk of colorectal cancer and discontinued in those at lower (or average) risk. In many subjects, however, DNA testing may still not be possible because of the failure to identify a predisposing mutation in an affected subject in their family. Any surveillance protocol can only be evaluated by long term follow up of those subjects in multiple centres.

Incidence and recurrence rates of colorectal adenomas: a prospective study

BACKGROUND/AIMS

The frequency of colorectal adenomas, the precursor lesions for most cases of colorectal carcinoma, has been generally measured as prevalence rates of adenomas at autopsy or colonoscopy. The aim of this study was to estimate the incidence rate of adenomas and compare it with the adenoma recurrence rate.

METHODS

Data on colonoscopies performed in three New York City practices were collected prospectively. The cumulative rate of adenoma diagnosis on repeat colonoscopy was calculated for patients with no abnormalities on index colonoscopy ("incidence" rate) and for patients with adenomas on the index colonoscopy ("recurrence" rate).

RESULTS

The cumulative incidence rate of adenomas at 36 months was 16%, and the cumulative recurrence rate at 36 months was 42% (P < 0.004). The recurrence rate was higher in patients with multiple adenomas than in those with a single adenoma on index colonoscopy, although the increase was not statistically significant.

CONCLUSIONS

Although the recurrence rate has always been assumed to be elevated, this study is the first to compare the recurrence rate of adenomas with the incidence rate directly and to show that the recurrence rate is indeed elevated.

Elevated c-yes tyrosine kinase activity in premalignant lesions of the colon

BACKGROUND/AIMS

The cellular oncogene c-yes and its viral homologue v-yes (the transforming gene of Yamaguchi 73 and Esh avian sarcoma viruses) encode 62-kilodalton, cytoplasmic, membrane-associated, protein-tyrosine kinases. For the related Src kinase, a close correlation exists between elevated kinase activity and cell transformation. Previously, we observed elevated Yes activity in many human colon carcinomas. Colonic neoplasia provides an opportunity to study tumor progression because most carcinomas arise from adenomas, which in turn arise from normal epithelia. The malignant potential of adenomas varies with size, histology, and degree of dysplasia. Large adenomas (> or = 2 cm) with villous architecture and severe dysplasia are most likely to develop carcinoma.

METHODS

To determine whether Yes is activated in premalignant lesions of the colon, we measured its in vitro protein-tyrosine kinase activity in 21 colonic adenomas from 17 patients.

RESULTS

Activity of Yes in adenomas at greatest risk for cancer was significantly greater (12- or 14-fold as measured by enolase or autophosphorylation, respectively) than activity in adjacent normal mucosa. Moreover, villous structure, large size (> or = 2 cm), or severe dysplasia correlated with elevated Yes activity.

CONCLUSIONS

The activity of Yes is elevated in adenomas that are at greatest risk for developing cancer.

Genetic susceptibility to colorectal cancer in patients under 45 years of age

A study was conducted to assess the genetic contribution to the development of colorectal cancer in young probands. Of 83 patients aged 45 years or under diagnosed with colorectal cancer in one health region over a 2-year period, 65 or their surviving next of kin were available for interview, from whom were obtained 60 detailed and five limited family histories. Five families fulfilled the Amsterdam criteria and a further eight satisfied less strict criteria for hereditary non-polyposis colorectal cancer, a total of 20 per cent of the cohort. Eleven of these families came from the subgroup of 13 probands who had one or more first-degree relatives with colorectal cancer. Overall the relative risk of colorectal cancer in close relatives was 5.2 (P < 0.0001). This risk was highest for female relatives at 9.7 (P < 0.0001) and relatives of female probands at 6.7 (P < 0.0001). This study highlights the importance of taking a family history in this group of patients. Screening by colonoscopy for all close relatives of young patients with colorectal cancer is recommended.

Screening/early detection model for colorectal cancer. Why screen?

Colon cancer is a leading cause of cancer death in the United States, causing approximately 60,000 deaths each year. Ideal screening would identify high risk patients and screen them with sensitive tests. Most cancers evolve from adenomatous polyps. There is now evidence that detection and removal of adenomas can prevent cancer. Unfortunately, our ability to identify high risk patients is limited. Screening of asymptomatic, average-risk individuals has been advocated, with the goal of reducing colon cancer mortality by detecting cancers at an early, curable stage or preventing cancer by detecting and removing adenomatous polyps. Recent data have suggested that screening populations older than age 50 with sigmoidoscopy and fecal occult blood tests can reduce colon cancer mortality. These reports are encouraging but also highlight significant limitations of this form of screening. Screening itself is designed merely to identify something that, once identified, needs further evaluation. Therefore, any discussion of colon screening must include consideration of how physicians will approach positive test results. The strategies for dealing with positive test results are costly and invariably lead to further surveillance. Current data suggest that patients with large polyps (> 1 cm) or villous adenomas have a high risk of colon cancer and are likely to benefit from full colonoscopy and subsequent surveillance. The benefits are far less clear for patients with small polyps. The subject of colon screening becomes even more complicated as consideration is given to when to start and stop screening, and how often to perform screening exams. There is clearly a need to improve upon the ability to identify patients most likely to develop colon cancer and design strategies to prevent cancer in this group. In the future, it may be possible to identify the high risk patient with some precision using genetic or biologic markers.

Does colonoscopic polypectomy reduce the incidence of colorectal carcinoma?

The study's objective was to examine whether there is evidence that colonoscopic polypectomy reduces the incidence of colorectal cancer. The records of all patients who underwent colonoscopic polypectomy by a single surgeon between 1974 and 1991 were reviewed. Patients with colorectal cancer diagnosed at the initial colonoscopy, with a history of colorectal cancer, inflammatory bowel disease or familial adenomatous polyposis or with only hyperplastic polyps were excluded. There were 1008 remaining patients, of whom 645 have attended at least one follow-up colonoscopic examination, and these 645 patients from the basis of the study, because the incidence of cancer is known exactly in this group. The mean period of follow up was 4.4 years and the mean number of follow-up colonoscopic examinations was 2.2. There was a total of 2847 person-years of colonoscopic follow up. The expected incidence of cancer, age and sex adjusted, is calculated using Australian epidemiological figures. The observed incidence of cancer was 3 cases (all asymptomatic) per 2847 person-years, which is indistinguishable from the general population's risk of 3.75 cases per 2847 person-years. Analysis of previous publications suggests that patients with adenomas are at an increased risk of developing colorectal cancer of about 2.5 times the general population's risk. If correct, then the observed incidence of 3 cases per 2847 person-years is less than the expected incidence of 9.4 cases per 2847 person-years. This analysis suggests colonoscopic polypectomy does reduce the incidence of colorectal cancer.

Prevention of colorectal cancer by colonoscopic polypectomy. The National Polyp Study Workgroup

BACKGROUND

The current practice of removing adenomatous polyps of the colon and rectum is based on the belief that this will prevent colorectal cancer. To address the hypothesis that colonoscopic polypectomy reduces the incidence of colorectal cancer, we analyzed the results of the National Polyp Study with reference to other published results.

METHODS

The study cohort consisted of 1418 patients who had a complete colonoscopy during which one or more adenomas of the colon or rectum were removed. The patients subsequently underwent periodic colonoscopy during an average follow-up of 5.9 years, and the incidence of colorectal cancer was ascertained. The incidence rate of colorectal cancer was compared with that in three reference groups, including two cohorts in which colonic polyps were not removed and one general-population registry, after adjustment for sex, age, and polyp size.

RESULTS

Ninety-seven percent of the patients were followed clinically for a total of 8401 person-years, and 80 percent returned for one or more of their scheduled colonoscopies. Five asymptomatic early-stage colorectal cancers (malignant polyps) were detected by colonoscopy (three at three years, one at six years, and one at seven years). No symptomatic cancers were detected. The numbers of colorectal cancers expected on the basis of the rates in the three reference groups were 48.3, 43.4, and 20.7, for reductions in the incidence of colorectal cancer of 90, 88, and 76 percent, respectively (P < 0.001).

CONCLUSIONS

Colonoscopic polypectomy resulted in a lower-than-expected incidence of colorectal cancer. These results support the view that colorectal adenomas progress to adenocarcinomas, as well as the current practice of searching for and removing adenomatous polyps to prevent colorectal cancer.

Incidence of colorectal cancer following adenomatous polyps of the large intestine

An association between adenomatous polyps of the large bowel and colorectal cancer has been reported, in the absence, however, of population-based estimates of risk. Subjects with histologically confirmed first diagnosis of large-bowel polyps notified to the population-based Cancer Registry of the Swiss Canton of Vaud (about 600,000 inhabitants) during the calendar period 1979-1990 were actively followed up to the end of 1990 for the subsequent occurrence of malignant neoplasms. Among 2,496 individuals with intestinal polyps, followed for a total of 10,310 person-years at risk (6,201 among males and 4,109 among females), 150 malignant neoplasms were registered versus 152 expected. Thus, the standardized incidence ratio (SIR) for all cancers combined was 0.99. A significant excess was observed for colorectal cancer, with 35 cases observed (19 males, 16 females) versus 17.0 expected (SIR = 2.1; 95% CI: 1.5-3.0). There was also an excess, although not significant, for small-bowel cancer (2 cases observed vs. 0.4 expected; SIR = 5.4). In none of the other cancer sites was SIR significantly or appreciably elevated: in subjects with colorectal polyps the SIR was 1.6 for stomach, 1.0 for lung, 0.9 for breast and 1.2 for prostate. The SIR of colorectal cancer was 3.1 in the first year since polyp registration, and declined thereafter to 1.8, in the absence, however, of any further trend with time since diagnosis. The cumulative risk of colorectal cancer in subjects with colorectal polyps was 2% at 5 years and 3% at 10 years. The quantitative estimates of this study are of interest for their population-based nature, and are potentially useful for defining and targeting screening colonoscopy programmes.