Screening for colorectal cancer. Issues for primary care physicians

Fecal occult blood testing, proctosigmoidoscopy, and digital rectal examination have been recommended as screening tests for colorectal cancer in asymptomatic people. This article evaluates the advisability of recommendations by applying accepted principles of screening to the case of colorectal cancer.

A comparison of methods for increasing compliance within a general practitioner based screening project for colorectal cancer and the effect on practitioner workload

Screening for colorectal cancer by testing for faecal occult blood (FOBT) is effective for early diagnosis, but the success of a screening programme also depends on compliance. The aims of this study were to assess the effect of health education on compliance and to assess any addition to general practitioner workload that resulted. Altogether 3860 patients were recruited and randomly allocated to test or control group. The test group was further divided into subgroups, some of which received health education. Compliance with FOBT was 54.7% (210/384) in the subgroup receiving only the doctor's letter, which fell to 48.1% (743/1544) in the group receiving health education. General practitioner consultation rates were similar in test and control groups.

Appropriate prevention and detection of gastrointestinal neoplasms in the elderly

The incidence of colorectal carcinoma and gastric cancer is related to environmental factors and lifestyle. Long-term exposure to multiple mutagens is believed to initiate the carcinogenesis of colorectal and gastric cancer. Even though patients older than 65 years of age have developed particular modes of cooking and dietary preferences, these habits can be changed with instruction, patient-doctor rapport, and suggestions of alternative foodstuffs that are palatable to them. Elderly patients can be persuaded to avoid fatty foods; smoked, pickled, and salted fish; and red meat. They should be encouraged to eat chicken, fish, fresh fruit, and vegetables (especially cruciferous vegetables), to ingest vitamin C, and to avoid overcooking, frying, and excessive broiling of meat and fish. Surveillance examinations must be practiced in the elderly to avoid malignant conversion of adenomatous polyps. All patients who have undergone gastric resections for peptic ulcer disease need to be watched carefully, with identification of high-risk individuals who must undergo periodic endoscopy.

An estimate of the proportion of colo-rectal and stomach cancers which might be prevented by certain changes in dietary habits

The colo-rectum and stomach are the 2 sites for which the role of diet in the etiology of cancer is most heavily implicated. Quantitative estimates as to the proportion of cancer deaths attributable to diet vary considerably. This may be partially due to the application of the concept of population attributable risk which has proved a useful yardstick in estimating the public health impact of completely removing an exposure factor under study. This simple concept may well serve in occupational epidemiology, but with more and more risk factors found on a metric scale, or at least characterized on an ordinal scale, extensions should be considered. In this report, a preventable proportion is defined as the excess risk which would be removed if the population exposure distribution were to change ina favorable direction. A simple way of modelling such changes is proposed. This new measure is illustrated with data from 6 case-control studies on colo-rectal or stomach cancer. The results indicate that the proportion of these cancers which may be prevented assuming arbitrary shifts of a single risk factor towards the next lower risk category if populations were to change their dietary habits is in the order of magnitude of 15% to 20%. This figure is much lower, but not necessarily in contradiction to the figures considered for the proportion of cancers attributable to diet.

The relative value of fecal occult blood tests and flexible sigmoidoscopy in screening for large bowel neoplasia

The secondary prevention of colorectal cancer is based on the early detection of noninvasive cancer and removal of adenomatous polyps. The two commonly used screening tests are flexible sigmoidoscopy and guaiac fecal occult blood testing. Both were performed simultaneously and independently on 1176 asymptomatic volunteers followed by colonoscopic examination if either occult blood or a neoplasm was detected. Neoplasia (adenomatous polyps or cancer) were found in 48 screenees. Only ten had positive stool occult blood while 45 were detected by sigmoidoscopy. Analysis of sensitivity for neoplasia was 93.8% for sigmoidoscopy but only 20.8% for the occult blood tests, while the positive predictive values for neoplasia were 100% and 23.8% respectively. The fecal occult blood test detected only 18% of screenees with adenomas and 60% with invasive cancer. Flexible sigmoidoscopy detected 95% and 80% respectively. Analysis (kappa statistic) demonstrated little agreement between the two tests (P greater than 0.05), indicating that they are diagnosing different neoplasia. Evaluation of expected gain in diagnosing neoplasia, by combining both tests, gave 18% for the fecal blood test and 94% for the endoscopic test. These results confirm the complementary value of performing both tests, but especially the high sensitivity and predictive value positive of flexible sigmoidoscopy for adenomas, including those with severe dysplasia, and the converse for the fecal occult blood test. This latter test must be recommended and used within a screening program with caution and full understanding of its limitations.

Preventive strategies for cancer in women

It is estimated that 480,000 types of cancer will occur in women during 1987, the most frequent being breast (27%), colon and rectum (16%), lung (11%), and uterus (10%). Of cancer deaths, lung (20%), breast (18%), and colorectal (14%) are most common. Uterine cancer is now the sixth cause of cancer death, after ovary and pancreas, due to the application of cancer detection. with an aging US population, cancer will become an even more significant health issue for women. Cancer in women aged 65 years and older occurs twice as frequently as in those aged 45 to 64 years. Melanoma is becoming an increasingly important public health problem because of its rising incidence during the last 20 years. Preventive strategies can be widely promoted to women in order to lower their cancer risk and to find cancer before symptoms appear. Smoking control, safe sun exposure, and simple recommendations for diet and nutrition can assist women in taking control of their lifestyles to reduce cancer risk. Early cancer detection, as outlined in the American Cancer Society's Cancer Related Checkup Guidelines, can be expected to find breast, colorectal, uterine, and other forms of cancer in asymptomatic women.

Prospects for the prevention of colorectal cancer

Cancer research has been productive in developing new knowledge on the role of diet in cancer. It is clear from epidemiologic observations that diet is the principal factor in the cause of colorectal cancer in most people. Therefore, a significant reduction in incidence is possible in countries where the disease is common. The ingestion of excessive amounts of fat appears to be the major factor that promotes cancer development. Animal studies confirm this and have recently shown that the sources of fat vary in the degree of their promotional effect. Fiber is generally considered to inhibit cancer but it is now clear that only some types of fiber are effective. These include whole grain cereals, and fruit and vegetables containing large amounts of uronic acid. In addition to fiber, a number of micronutrients, chemicals, and drugs have been found to be effective inhibitors. It is clear that the basic information concerning dietary changes that can reduce colorectal cancer incidence in this country has been uncovered. Additional information is needed about specific details of dietary guidelines. These include identification of the best mixture of sources of fat and how to incorporate such a mixture in the diet. Substances in foods need to be identified that, when included in the diet, help to lower cancer risk. People at high risk may require an additional supplement of inhibitors. New epidemiologic studies and human intervention trials should provide the necessary information to design dietary guidelines that are more specific than current ones.

[Does prolonging the test period improve screening for colorectal cancer?]

Prolongation of Haemoccult-screening from 3 to 6 days in 3540 out-patients resulted in a rise of the positivity rate from 4.1 to 6.75%. This was accompanied by an increase of the detection rate by 10% in cancers and 25% in large adenomas. The predictive value of a positive test for colorectal neoplasia (carcinoma and large polyps together) dropped from 26.7 to 20.9%. More data are needed before general recommendation for change from the standard 3-day-test period can be given.

Prevention of colorectal cancer. Role of association between gallstones and colorectal cancer

A significant association was found between colorectal cancer, especially of the right colon, and concomitant gallstones. This was noted especially in female patients and in those over the age of 65. The existence of such an association is of advantage in terms of secondary prevention of colorectal cancer. The possible screening methods are discussed for those gallstone patients at risk.

Effect of workup strategy on the cost-effectiveness of fecal occult blood screening for colorectal cancer

Physicians respond to a positive fecal occult blood test with a variety of workup strategies. To study the effect of the choice of strategy on the net costs and health benefits of colorectal cancer screening using this test, we used a decision analysis model to compare seven strategies that physicians might choose to examine a positive "screenee." Strategies using rigid or flexible sigmoidoscopy alone are not only insensitive, but also have high cost-effectiveness ratios. The strategy of air contrast barium enema alone had the lowest cost-effectiveness ratio. Rigid sigmoidoscopy combined with barium enema had a lower cost-effectiveness ratio than primary colonoscopy, but the strategy of primary colonoscopy could have an equal or better ratio depending on assumptions about test costs and the benefit of removing benign polyps. The primary colonoscopy strategy is both more effective and less costly than the combination of flexible sigmoidoscopy and barium enema. The optimal strategy will vary with local factors, and with the perspective of the decision-maker.

Family history of colorectal cancer as a marker of potential malignancy within a screening program

Epidemiologic studies have shown that asymptomatic adult relatives of colorectal cancer patients are at increased risk for developing this tumor. A prospective, published pilot study confirmed this added risk and demonstrated the importance of the family history of cancer as a marker of potential malignancy. The study group was enlarged to include 471 asymptomatic adult, first degree relatives of patients having large bowel neoplasia (cancer or adenomatous polyps) but without polyposis syndromes. These first degree relatives were screened by fecal occult blood examinations and flexible sigmoidoscopy, followed by colonoscopy when indicated. Adenomatous polyps or cancer were found in 8.1% of the study group as compared with 3.7% in a comparison group of screens, not having the same family history of neoplasia and undergoing similar screening tests. Of the study group the age-adjusted rate for colorectal adenomas or cancer increased threefold (P less than 0.001) for subjects older than 40 years and an even higher fivefold relative risk was found for large bowel cancer only (P = 0.01). This was true even if there was only one relative with colorectal neoplasia (P less than 0.01) but was even more pronounced among those having more than one affected relative. The results confirm the usefulness of the family history, of even one member with large bowel neoplasia, in isolating a group at high risk for these lesions. This group would most likely benefit from regular cancer and adenomatous polyp screening particularly when older than 40 years.

The familial polyposis coli register

Familial polyposis coli is an inherited condition in which many hundreds of adenomatous polyps develop in the colorectum usually during the second decade of life. There is a high incidence of associated carcinoma, a risk which approximates to 100% in untreated patients. Adenomas and carcinomas also occur in the upper gastro-intestinal tract though to a lesser extent. A policy of cancer prevention based on the genetic origin and natural course of the disease requires the identification of family members at risk in order that detection and surgical removal of the polyps can be effected before any malignant change has occurred. The identification of persons at risk requires knowledge of affected families. The establishment and maintenance of regional registers of polyposis coli families is advocated.

Human papillomavirus infection and anogenital neoplasia: speculations for the future

HPV infections of the female genital tract are common. The association of these viruses with anogenital neoplasia has stimulated efforts to devise practical methods of detection and typing of HPV. Although experimental diagnostic tests are available, they are, for the most part, complex and time consuming and are limited to medical centers researching HPV. New methods for preparing probes with higher sensitivities for hybridization tests will allow use of in-situ methods on formalin-fixed tissues and will probably be the method of choice. Antigen detection systems are not available except for antisera directed against the common structural antigens. The most useful immunologic test will be directed toward detection of nonstructural antigens in fixed tissues; such a system could also be useful for virus typing. Therapies based on use of these antigens to stimulate the immune system may be applicable as an alternative to current therapies. Most intriguing are the prospects for a vaccine based on either structural or nonstructural viral antigens. It has been estimated that as many as 20 per cent of female cancer deaths worldwide are associated with HPV. Thus, use of an effective vaccine would relieve considerable human suffering. However, until the host immune response to HPV infection is better defined, much of the effort dedicated to developing a vaccine may be futile.