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Tuesday, 25 January 2011 14:45

Cancer Prevention and Control

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Within the next decade, it is predicted, cancer will become the leading cause of death in many developed countries. This reflects not so much an increase in the incidence of cancer but rather a decrease in mortality due to cardiovascular disease, currently topping the mortality tables. Equally with its high mortality rate, we are disturbed by the specter of cancer as a “dread” disease: one associated with a more or less rapid course of disability and a high degree of suffering. This somewhat fearsome picture is being made easier to contemplate by our growing knowledge of how to reduce risk, by techniques permitting early detection and by new and powerful achievements in the field of therapy. However, the latter may be associated with physical, emotional and economic costs for both the patients and those concerned about them. According to the US National Cancer Institute (NCI), a significant reduction in cancer morbidity and mortality rates is possible if current recommendations relating to use of tobacco, dietary changes, environmental controls, screening and state-of-the-art treatment are effectively applied.

To the employer, cancer presents significant problems entirely apart from the responsibility for possible occupational cancer. Workers with cancer may have impaired productivity and recurrent absenteeism due both to the cancer itself and the side effects of its treatment. Valuable employees will be lost through prolonged periods of disability and premature death, leading to the considerable cost of recruiting and training replacements.

There is a cost to the employer even when it is a spouse or other dependant rather than the healthy employee who develops the cancer. The caregiving burden may lead to distraction, fatigue and absenteeism which tax that employee’s productivity, and the often considerable medical expenses increase the cost of employer-sponsored health insurance. It is entirely appropriate, therefore, that cancer prevention should be a major focus of worksite wellness programs.

Primary Prevention

Primary prevention involves avoidance of smoking and modifying other host factors that may influence the development of cancer, and identifying potential carcinogens in the work environment and eliminating or at least limiting workers’ exposure to them.

Controlling exposures

Potential as well as proven carcinogens are identified through basic scientific research and by epidemiological studies of exposed populations. The latter involves industrial hygiene measurements of the frequency, magnitude and duration of the exposures, coupled with comprehensive medical surveillance of the exposed workers, including analysis of causes of disability and death. Controlling exposures involves the elimination of these potential carcinogens from the workplace or, when that is not possible, minimizing exposure to them. It also involves the proper labeling of such hazardous materials and continuing education of workers with respect to their handling, containment and disposal.

Smoking and cancer risk

Approximately one-third of all cancer deaths and 87% of all lung cancers in the US are attributable to smoking. Tobacco use is also the principal cause of cancers of the larynx, oral cavity and oesophagus and it contributes to the development of cancers of the bladder, pancreas, kidney, and uterine cervix. There is a clear dose-response relationship between lung cancer risk and daily cigarette consumption: those who smoke more than 25 cigarettes a day have a risk that is about 20 times greater than that of non-smokers.

Experts believe that the involuntary intake of the tobacco smoke emitted by smokers (“environmental tobacco smoke”) is a significant risk factor for lung cancer in non-smokers. In January 1993, the US Environmental Protection Agency (EPA) classified environmental tobacco smoke as a known human carcinogen which, it estimated, is responsible for approximately 3,000 lung cancer deaths annually among US non-smokers.

The 1990 US Surgeon General’s report on the health benefits of smoking cessation provides clear evidence that quitting smoking at any age is beneficial to one’s health. For example, five years after quitting, former smokers experience a diminished risk for lung cancer; their risk, however, remains higher than that of non-smokers for as long as 25 years.

The elimination of tobacco exposure by employer-sponsored/ labor union-sponsored smoking cessation programs and worksite policies enforcing a smoke-free working environment represent a major element in most worksite wellness programs.

Modifying host factors

Cancer is an aberration of normal cell division and growth in which certain cells divide at abnormal rates and grow abnormally, sometimes migrating to other parts of the body, affecting the form and function of involved organs, and ultimately causing death of the organism. Recent, continuing biomedical advances are providing increasing knowledge of the carcinogenesis process and are beginning to identify the genetic, humoral, hormonal, dietary and other factors that may accelerate or inhibit it—thus leading to research on interventions that have the potential to identify the early, precancerous process and so to help restore the normal cellular growth patterns.

Genetic factors

Epidemiologists continue to accumulate evidence of familial variations in the frequency of particular types of cancer. These data have been bolstered by molecular biologists who have already identified genes that appear to control steps in cellular division and growth. When these “tumor suppressor” genes are damaged by naturally-occurring mutations or the effects of an environmental carcinogen, the process may go out of control and a cancer is initiated.

Heritable genes have been found in patients with cancer and members of their immediate families. One gene has been associated with a high risk of colon cancer and endometrial or ovarian cancer in women; another with a high risk of breast and ovarian cancer; and a third with a form of malignant melanoma. These discoveries led to a debate about the ethical and sociological issues surrounding DNA testing to identify individuals carrying these genes with the implication that they then might be excluded from jobs involving possible exposure to potential or actual carcinogens. After studying this question, the National Advisory Council for Human Genome Research (1994), raising issues to do with the reliability of the testing, the present effectiveness of potential therapeutic interventions, and the likelihood of genetic discrimination against those found to be at high risk, concluded that “it is premature to offer DNA testing or screening for cancer predisposition outside a carefully monitored research environment”.

Humoral factors

The value of the prostate specific antigen (PSA) test as a routine screening test for prostatic cancer in older men has not been scientifically demonstrated in a clinical trial. However, in some instances, it is being offered to male workers, sometimes as a token of gender equity to balance the offering of mammography and cervical Pap smears to female workers. Clinics providing routine periodic examinations are offering the PSA test as a supplement to and, sometimes, even as a replacement for the traditional digital rectal examination as well as the recently introduced rectal ultrasound examination. Although its use appears to be valid in men with prostatic abnormalities or symptoms, a recent multinational review concludes that measurement of PSA should not be a routine procedure in screening healthy male populations (Adami, Baron and Rothman 1994).

Hormonal factors

Research has implicated hormones in the genesis of some cancers and they have been used in the treatment of others. Hormones, however, do not appear to be an appropriate item to emphasize in workplace health promotion programs. A possible exception would be warnings of their potential carcinogenic hazard in certain cases when recommending hormones for the treatment of menopausal symptoms and the prevention of osteoporosis.

Dietary factors

Researchers have estimated that approximately 35% of all cancer mortality in the US may be related to diet. In 1988, the US Surgeon General’s Report on Nutrition and Health indicated that cancers of the lung, colon-rectum, breast, prostate, stomach, ovary and bladder may be associated with diet. Research indicates that certain dietary factors—fat, fiber, and micronutrients such as beta-carotene, vitamin A, vitamin C, vitamin E and selenium—may influence cancer risk. Epidemiological and experimental evidence indicates that modulation of these factors in the diet can reduce the occurrence of some types of cancer.

Dietary fat

Associations between excess intake of dietary fat and the risk of various cancers, particularly cancers of the breast, colon and prostate, have been demonstrated in both epidemiological and laboratory studies. International correlational studies have shown a strong association between the incidence of cancers at these sites and total dietary fat intake, even after adjusting for total caloric intake.

In addition to the amount of fat, the type of fat consumed may be an important risk factor in cancer development. Different fatty acids may have various site-specific tumor-promoting or tumor-inhibiting properties. Intake of total fat and saturated fat has been strongly and positively associated with colon, prostate, and post-menopausal breast cancers; intake of polyunsaturated vegetable oil has been positively associated with post-menopausal breast and prostate cancers, but not with colon cancer. Conversely, consumption of highly polyunsaturated omega-3 fatty acids found in certain fish oils may not affect or may even decrease the risk of breast and colon cancers.

Dietary fiber

Epidemiological evidence suggests that the risk of certain cancers, particularly colon and breast cancers, may be lowered by increased intake of dietary fiber and other dietary constituents associated with high intakes of vegetables, fruits, and whole grains.

Micronutrients

Epidemiological studies generally show an inverse relationship between cancer incidence and intake of foods high in several nutrients having antioxidant properties, such as beta-carotene, vitamin C (ascorbic acid), and vitamin E (alpha-tocopherol). A number of studies have shown that low intakes of fruits and vegetables are associated with increased risk of lung cancer. Deficiencies of selenium and zinc have also been implicated in increased cancer risk.

In a number of studies in which the use of antioxidant supplements was shown to reduce the expected number of serious heart attacks and strokes, the data on cancer were less clear. However, results from the Alpha-Tocopherol, Beta-Carotene (ATBC) Lung Cancer Prevention clinical trial, conducted by the NCI in collaboration with the National Public Health Institute of Finland, indicated that vitamin E and beta-carotene supplements did not prevent lung cancer. Vitamin E supplementation also resulted in 34% fewer prostate cancers and 16% fewer colorectal cancers, but those subjects taking beta-carotene had 16% more lung cancers, which was statistically significant, and had slightly more cases of other cancers than those taking vitamin E or the placebo. There was no evidence that the combination of vitamin E and beta-carotene was better or worse than either supplement alone. The researchers have not yet determined why those taking beta-carotene in the study were observed to have more lung cancers. These results suggest the possibility that a different compound or compounds in foods which have high levels of beta-carotene or vitamin E may be responsible for the protective effect observed in epidemiological studies. The researchers also speculated that the length of time of supplementation may have been too short to inhibit the development of cancers in long-term smokers. Further analyses of the ATBC study, as well as results from other trials in progress, will help resolve some of the questions that have arisen in this trial, particularly the question of whether large doses of beta-carotene may be harmful to smokers.

Alcohol

Excessive use of alcoholic beverages has been associated with cancer of the rectum, pancreas, breast and liver. There is also strong evidence supporting a synergistic association of alcohol consumption and tobacco use with increased risk of cancer of the mouth, pharynx, oesophagus and larynx.

Dietary recommendations

Based on the compelling evidence that diet is related to cancer risk, the NCI has developed dietary guidelines that include the following recommendations:

  • Reduce fat intake to 30% or less of calories.
  • Increase fibre intake to 20 to 30 grams per day, with an upper limit of 35 grams.
  • Include a variety of vegetables and fruits in the daily diet.
  • Avoid obesity.
  • Consume alcoholic beverages in moderation, if at all.
  • Minimize consumption of salt-cured (packed in salt), salt-pickled (soaked in brine), or smoked foods (associated with increased incidence of stomach and oesophageal cancer).

 

These guidelines are intended to be incorporated into a general dietary regimen that can be recommended for the entire population.

Infectious diseases

There is increasing knowledge of the association of certain infectious agents with several types of cancer: for example, the hepatitis B virus with liver cancer, the human papillomavirus with cervical cancer, and the Epstein-Barr virus with Burkitt’s lymphoma. (The frequency of cancer among patients with AIDS is attributable to the patient’s immunodeficiency and is not a direct carcinogenic effect of the HIV agent.) A vaccine for hepatitis B is now available that, when given to children, ultimately will reduce their risk for liver cancer.

Worksite Cancer Prevention

To explore the potential of the workplace as an arena for the promotion of a broad set of cancer prevention and control behaviors, the NCI is sponsoring the Working Well Project. This project is designed to determine whether worksite-based interventions to reduce tobacco use, achieve cancer preventive dietary modifications, increase screening prevalence and reduce occupational exposure can be developed and implemented in a cost-effective way. It was initiated in September 1989 at the following four research centers in the United States.

  • M.D. Anderson Cancer Center, Houston, Texas
  • University of Florida, Gainesville, Florida
  • Dana Farber Cancer Institute, Boston, Massachusetts
  • Miriam Hospital/Brown University, Providence, Rhode Island

 

The project involves approximately 21,000 employees at 114 different worksites around the United States. Most of the selected worksites are involved predominantly in manufacturing; other types of worksites in the project included fire stations and newspaper printers. Tobacco reduction and dietary modification were areas of intervention included in all of the worksites; however, each site maximized or minimized particular intervention programs or included additional options to meet the climatic and socioeconomic conditions of the geographic area. The centers in Florida and Texas, for example, included and emphasized skin cancer screening and the use of sun screens because of increased exposure to the sun in those geographic regions. The centers in Boston and Texas offered programs that emphasized the relationship between cancer and tobacco use. The Florida centre enhanced the diet modification intervention with supplies of fresh citrus fruits, readily available from the state’s farming and fruit industry. Management-employee consumer boards also were established at the worksites of the Florida centre to work with the food service to ensure that the cafeterias offered fresh vegetable and fruit selections. Several of the worksites participating in the project offered small prizes—gift certificates or cafeteria lunches—for continued participation in the project or for achievement of a desired goal, such as smoking cessation. Reduction of exposure to occupational hazards was of special interest at those worksites where diesel exhaust, solvent use or radiation equipment were prevalent. The worksite-based programs included:

  • group activities to generate interest, such as taste testing of various foods
  • directed group activities, such as quit-smoking contests
  • medical/scientific-based demonstrations, such as  testing, to verify the effect of smoking on the respiratory system
  • seminars on business practices and policy development aimed at significantly reducing or eliminating occupational exposure to potentially or actually dangerous or toxic materials
  • computer-based self-help and self-assessment programmes on cancer risk and prevention
  • manuals and self-help classes to help reduce or eliminate tobacco use, achieve dietary modifications, and increase cancer screening.

 

Cancer education

Worksite health education programs should include information about signs and symptoms that are suggestive of early cancer—for example, lumps, bleeding from the rectum and other orifices, skin lesions that do not appear to heal—coupled with advice to seek evaluation by a physician promptly. These programs might also offer instruction, preferably with supervised practice, in self-examination of the breast.

Cancer screening

Screening for precancerous lesions or early cancer is carried out with a view to their earliest possible detection and removal. Educating individuals about the early signs and symptoms of cancer so that they may seek the attention of a physician is an important part of screening.

A search for early cancer should be included in every routine or periodic medical examination. In addition, mass screenings for particular types of cancer may be carried out in the workplace or in a community facility near the worksite. Any acceptable and justifiable screening of an asymptomatic population for cancer should meet the following criteria:

  • The disease in question should represent a substantial burden at the public health level and should have a prevalent, asymptomatic, nonmetastatic phase.
  • The asymptomatic, nonmetastatic phase should be recognizable.
  • The screening procedure should have reasonable specificity, sensitivity and predictive values; it should be of low risk and low cost, and be acceptable to both the screener and the person being screened.
  • Early detection followed by appropriate treatment should offer a substantially greater potential for cure than exists in cases in which discovery was delayed.
  • Treatment of lesions detected by screening should offer improved outcomes as measured in cause-specific morbidity and mortality.

 

The following additional criteria are particularly relevant in the workplace:

  • Employees (and their dependants, when involved in the programme) should be informed of the purpose, nature and potential results of the screening, and a formal “informed consent” should be obtained.
  • The screening programme should be conducted with due consideration for the comfort, dignity and privacy of the individuals consenting to be screened and should involve minimal interference with working arrangements and production schedules.
  • Screening results should be conveyed promptly and privately, with copies forwarded to personal physicians designated by the workers. Counselling by trained health professionals should be available to those seeking clarification of the screening report.
  • The individuals screened should be informed of the possibility of false negatives and warned to seek medical evaluation of any signs or symptoms developing soon after the screening exercise.
  • A prearranged referral network should be in place to which those with positive results who are not able or do not wish to consult their personal physicians may be referred.
  • The costs of the necessary confirmatory examinations and the costs of treatment should be covered by health insurance or otherwise be affordable.
  • A prearranged follow-up system should be in place to be sure that positive reports have been promptly confirmed and proper interventions arranged.

 

A further final criterion is of fundamental importance: the screening exercise should be conducted by properly skilled and accredited health professionals using state-of-the-art equipment and interpretation and analysis of the results should be of the highest possible quality and accuracy.

In 1989 the US Preventive Services Task Force, a panel of 20 experts from medicine and other related fields drawing upon hundreds of “advisors” and others from the United States, Canada and the United Kingdom, assessed the effectiveness of some 169 preventive interventions. Its recommendations with respect to screening for cancer are summarized in table 1. Reflecting the Task Force’s somewhat conservative attitude and rigorously applied criteria, these recommendations may differ from those advanced by other groups.

Table 1. Screening for neoplastic diseases.

Types of cancer

Recommendations of the US Preventive Services Task Force*

Breast

All women over age 40 should receive an annual clinical breast examination. Mammography every one to two years is recommended for all women beginning at age 50 and continuing until age 75 unless pathology has been detected. It may be prudent to begin mammography at an earlier age for women at high risk for breast cancer. Although the teaching of breast self-examination is not specifically recommended at this time, there is insufficient evidence to recommend any change in current breast self- examination practices (i.e., those who are now teaching it should continue the practice).

Colorectal

There is insufficient evidence to recommend for or against fecal occult blood testing or sigmoidoscopy as effective screening tests for colorectal cancer in asymptomatic individuals. There are also insufficient grounds for discontinuing this form of screening where it is currently practiced or for withholding it from persons who request it. It may be clinically prudent to offer screening to persons aged 50 or older with known risk factors for colorectal cancer.

Cervical

Regular Papanicolaou (Pap) testing is recommended for all women who are or have been sexually active. Pap smears should begin with the onset of sexual activity and should be repeated every one to three years at the physician’s discretion. They may be discontinued at age 65 if previous smears have been consistently normal.

Prostate

There is insufficient evidence to recommend for or against routine digital rectal examination as an effective screening test for prostate cancer in asymptomatic men. Transrectal ultrasound and serum tumor markers are not recommended for routine screening in asymptomatic men.

Lung

Screening asymptomatic persons for lung cancer by performing routine chest radiography or sputum cytology is not recommended.

Skin

Routine screening for skin cancer is recommended for persons at high risk. Clinicians should advise all patients with increased outdoor exposure to use sunscreen preparations and other measures to protect from ultraviolet rays. Currently there is no evidence for or against advising patients to perform skin self-examination.

Testicular

Periodic screening for testicular cancer by testicular examination is recommended for men with a history of cryptorchidism, orchiopexy, or testicular atrophy. There is no evidence of clinical benefit or harm to recommend for or against routine screening of other men for testicular cancer. Currently there is insufficient evidence for or against counseling patients to perform periodic self-examination of the testicles.

Ovarian

Screening of asymptomatic women for ovarian cancer is not recommended. It is prudent to examine the adnexa when performing gynecologic examinations for other reasons.

Pancreatic

Routine screening for pancreatic cancer in asymptomatic persons is not recommended.

Oral

Routine screening of asymptomatic persons for oral cancer by primary care clinicians is not recommended. All patients should be counseled to receive regular dental examinations,  to discontinue the use of all forms of tobacco,  and to limit consumption of alcohol.

Source: Preventive Services Task Force 1989.

Screening for breast cancer

There is a general consensus among experts that screening with mammography combined with clinical breast examination every one to two years will save lives among women aged 50 to 69, reducing breast cancer deaths in this age group by up to 30%. Experts have not reached agreement, however, on the value of breast cancer screening with mammography for asymptomatic women aged 40 to 49. The NCI recommends that women in this age group should be screened every one to two years and that women at increased risk for breast cancer should seek medical advice about whether to begin screening before age 40.

The female population in most organizations may be too small to warrant the installation of mammography equipment onsite. Accordingly, most programs sponsored by employers or labor unions (or both) rely on contracts with providers who bring mobile units to the workplace or on providers in the community to whom participating female employees are referred either during working hours or on their own time. In making such arrangements, it is essential to be sure that the equipment meets standards for x-ray exposure and safety such as those promulgated by the American College of Radiology, and that the quality of the films and their interpretation is satisfactory. Further, it is imperative that a referral resource be prearranged for those women who will require a small needle aspiration or other confirmatory diagnostic procedures.

Screening for cervical cancer

Scientific evidence strongly suggests that regular screening with Pap tests will significantly decrease mortality from cervical cancer among women who are sexually active or who have reached the age of 18. Survival appears to be directly related to the stage of the disease at diagnosis. Early detection, using cervical cytology, is currently the only practical means of detecting cervical cancer in localized or premalignant stages. The risk of developing invasive cervical cancer is three to ten times greater in women who have never been screened than in those who have had Pap tests every two or three years.

Of particular relevance to the cost of workplace screening programs is the fact that cervical cytology smears can be obtained quite efficiently by properly trained nurses and do not require the involvement of a physician. Perhaps of even greater importance is the quality of the laboratory to which they are sent for interpretation.

Screening for colorectal cancer

It is generally agreed that early detection of precancerous colorectal polyps and cancers by periodic tests for fecal blood, as well as digital rectal and sigmoidoscopic examinations, and their timely removal, will reduce mortality from colorectal cancer among individuals aged 50 and over. The examination has been made less uncomfortable and more reliable with the replacement of the rigid sigmoidoscope by the longer, flexible fibreoptic instrument. There remains, however, some disagreement as to which tests should be relied upon and how often they should be applied.

Pros and cons of screening

There is general agreement about the value of cancer screening in individuals at risk because of family history, prior occurrence of cancer, or known exposure to potential carcinogens. But there appear to be justifiable concerns about the mass screening of healthy populations.

Advocates of mass screening for the detection of cancer are guided by the premise that early detection will be followed by improvements in morbidity and mortality. This has been demonstrated in some instances, but is not always the case. For example, although it is possible to detect lung cancer earlier by use of chest x rays and sputum cytology, this has not led to any improvement in treatment outcomes. Similarly, concern has been expressed that increasing the lead time for treatment of early prostatic cancers may not only be without benefit but may, in fact, be counterproductive in view of the longer period of well-being enjoyed by patients whose treatment is delayed.

In planning mass screening programs, consideration must also be given to the impact on the well-being and pocketbooks of patients with false positives. For example, in several series of cases, 3 to 8% of women with positive breast screenings had unnecessary biopsies for benign tumors; and in one experience with the fecal blood test for colorectal cancer, nearly one-third of those screened were referred for diagnostic colonoscopy, and most of them showed negative results.

It is clear that additional research is needed. To assess the efficacy of screening, the NCI has launched a major study, the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trials (PLCO) to evaluate early detection techniques for these four cancer sites. Enrolment for the PLCO began in November 1993, and will involve 148,000 men and women, aged 60 to 74 years, randomized to either the intervention or the control group. In the intervention group, men will be screened for lung, colorectal and prostatic cancer while women will be screened for lung, colorectal and ovarian cancer; those assigned to the control group will receive their usual medical care. For lung cancer, the value of an annual single-view chest x ray will be studied; for colorectal cancer, annual fibreoptic sigmoidoscopy will be performed; for prostate cancer, digital rectal examination and a blood test for PSA will be done; and for ovarian cancer, yearly physical and transvaginal ultrasound examinations will be supplemented by an annual blood test for the tumor marker known as CA-125. At the end of 16 years and the expenditure of US$ 87.8 million, it is hoped that solid data will be obtained about how screening may be used to obtain early diagnoses that may extend lives and reduce mortality.

Treatment and Continuing Care

Treatment and continuing care comprise efforts to enhance the quality of life for those in whom a cancer has taken hold and for those involved with them. Occupational health services and employee assistance programs sponsored by employers and unions can provide useful counsel and support to workers being treated for cancer or who have a dependant receiving treatment. This support can include explanations of what is going on and what to expect, information that is sometimes not provided by oncologists and surgeons; guidance in referrals for second opinions; and consultations and assistance with regard to access to centers of highly specialized care. Leaves of absence and modified work arrangements may make it possible for workers to remain productive while in treatment and to return to work earlier when a remission is achieved. In some workplaces, peer support groups have been formed to provide an exchange of experiences and mutual support for workers facing similar problems.

Conclusion

Programs for the prevention and detection of cancer can make a meaningful contribution to the well-being of the workers involved and their dependants and yield a significant return to the employers and labor unions that sponsor them. As with other preventive interventions, it is necessary that these programs be properly designed and carefully implemented and, since their benefits will accrue over many years, they should be continued on a steady basis.

 

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