Colorectal cancer is a common disease associated with considerable morbidity and mortality. It has a natural history of transition from precursor to malignant that spans 10 to 15 years on average, providing a window of opportunity for effective prevention and early diagnosis interventions. Lifestyle modifications (balanced diet with intake of more dietary fibre, vegetables and fruit, calcium and vitamins, and less fat and; avoidance of obesity, smoking and alcohol; and moderate physical activity) and compliance with screening methods might prevent up to 90% of invasive cancers.
Different options for screening exist, each with advantages and disadvantages that vary for individual patient and practice settings. The choice should be based on available resources, patient preference and adherence and medical contra-indications.
Generally accepted guidelines for screening depend on individual patient risk as follows:
General population: age 50 and over: one of the following schedules:
- Faecal occult blood test yearly (reduces colorectal cancer mortality by 16%) and flexible sigmoidoscopy every 5 years; all positive tests should be followed up with colonoscopy.
- Colonoscopy every 10 years (regarding the natural history of adenomatous polyps to slowly progress over years).
- Double contrast barium enema every 5-10 years; all positive tests should be followed up with colonoscopy.
- Computed tomography colonography is an emerging technology that shows considerable promise, but needs to be studied in a typical screening population to provide comparison with conventional tests.
- Discontinuation of screening is reasonable in patients whose age or comorbid conditions limit life expectancy.
High risk patients:
- Higher than average risk: history of adenomatous polyps, previous curative resection of colorectal cancer, or family history of colorectal cancer or colorectal adenomas diagnosed in a first-degree relative before age 60. Recommendation: start screening earlier and more frequently.
- Very high risk: family history of familial polyposis or hereditary non- polyposis colorectal cancer, or personal history of inflammatory bowel syndrome. Recommendation: early screening with colonoscopy and genetic counselling and testing for genetic syndromes.
Potential harm of screening:
- False positive faecal occult blood tests can lead to invasive procedures such as colonoscopy.
- Sigmoidoscopy can cause pain (14%), flatulence (25%), bleeding (3%), anxiety or perforation (1-2 in 10 000).
- Barium enema causes important complications of any type in only 1 in 10 000 patients; perforation 1 in 25 000 and death in 1 in 55 000.
- Screening colonoscopy causes major complications in only 0,2 to 0,3 % of patients during or immediately after the procedure, the most common being bleeding.
The purpose of screening is to reduce premature mortality from disease. Increased public awareness and improvements in diagnosis and treatment have achieved this over the past 25 years. For a screening program to be successful, a high level of compliance (more than 75%) must be achieved, and the procedures must be highly sensitive and specific for diagnosing the disease. In mammography, this means high quality radiologic imaging and interpretation, and precision in image-guided biopsy.
The following recommendations are given by the American Cancer Society:
- Age 20 and older: Monthly breast self-examination. The importance of reporting any new breast symptoms to a health professional should be emphasized. Women should receive instruction and review of the technique during periodic clinical examination by a health professional.
- Age 20 – 39: Clinical breast examination every 3 years, as part of a periodic general examination.
- Age 40 and older: Mammography and clinical breast examination yearly.
High risk factors such as a family history of first degree relatives with breast cancer at an early age, previous breast biopsies and long-term unopposed ooestrogen exposure, necessitate greater vigilance and starting regular mammography and clinical examination at an earlier age. Genetic testing might also be indicated in cases of strong family history of breast, ovarian or colon carcinoma.
Potential harm of screening:
Although there is a proven 15% reduction in breast cancer mortality from screening, high rates (20 – 50%) of false positive tests cause much anxiety and lead to unnecessary and costly invasive diagnostic procedures with discomfort. Screening may also diagnose tumours that may not be clinically relevant.
Magnetic Resonance Imaging in breast cancer screening: This procedure is being evaluated and appears to have a specificity of 95%. At present it is considered complementary to mammography in women with genetic risk factors for breast cancer, i.e. BRCA1 carriers and BRCA 2 carriers with radiologically dense breasts.
The role of early detection and appropriate treatment is well established in cervical cancer, with a mortality reduction of 70% in countries with an effective screening program.
Current recommendations include the following:
- Age 21 and older and all women who are or have been sexually active for 3 years: Papanicolau (Pap) test (cervical cytology smear) and pelvic examination, repeated every 3 years or more regularly depending on previous cytology result.
- After 3 consecutive normal smears: Pap test less often at discretion of physician.
- If cytology is not possible for logistical reasons, pelvic examination with visual inspection, acetic acid and magnification or Lugol’s iodine can help to diagnose disease at an early , although not microscopic, stage.
High risk factors include early age at first intercourse, multiple partners and early childbearing, and should prompt more vigilant surveillance. Human papilloma virus (HPV) is associated with more than 95% of cervical cancers, and can now be detected more sensitively and treated appropriately. A vaccine has also become available, and should ideally be administered prior to exposure to the virus.
Although breast cancer is more prevalent in women, mortality from lung cancer exceeds that of breast plus colorectal cancers in women. Lung cancer is the fastest growing cancer in women because of increased prevalence of smoking in the last few decades. Primary prevention (not starting to smoke or quitting early) may almost totally eliminate this disease, but unfortunately rates of smoking in adolescents worldwide are increasing instead. More than two thirds of patients are diagnosed with locally advanced or metastatic disease, and overall less than 15% survive 5 years.
The only screening method shown to diagnose disease at a significantly earlier stage is spiral CT (computed tomography) scanning. However, it still remains unclear whether widespread population screening with this costly intervention will lead to an overall reduction in mortality. At the moment its use should be reserved for early symptomatic patients with an abnormal chest X-ray examination.
Recommendation for Cancer screening and Prevention:
- Develop screening programs for breast, colorectal and cervical cancers, with available manpower and infrastructure for the subsequent treatment of diagnosed cases.
- Protect the environment and workers from cancer-causing agents, specifically in public areas and work places.
- Promote awareness of and access to healthy living (diet, sports facilities) and discourage high risk behaviour (smoking, promiscuity).
- Inform and encourage all policy-making bodies to adhere to abovementioned guidelines.
- Inform and encourage patients and the public to participate in preventive and screening programs and to avoid high risk behaviour.
- Take part in abovementioned screening programs.
- Do's: Daily brisk physical activity, increase daily intake and variety of fresh vegetables and fruit to at least 5 servings a day.
- Don’t’s: Don't smoke, or smoke less and not near others. Avoid obesity, alcohol, excessive sun exposure and other cancer-causing factors.