Friday, 20 July 2012

Cancer Prevention

Prevention of cancer :

Primary Prevention:
Mortality rates of cancer have begun to decrease in the past 2 years; part of this decrease results from reductions in tobacco use, since cigarette smoking is the most important preventable cause of cancer. Preventive health examinations and preventive gynecologic examinations are among the most common reasons for ambulatory care visits, although the use and content of these types of visits remains controversial. Primary prevention of skin cancer consists of restricting exposure to ultraviolet light by wearing appropriate clothing and use of sunscreens. In the past 2 decades, there has been a threefold increase in the incidence of squamous cell carcinoma and a fourfold increase in melanoma in the United States. Persons who engage in regular physical exercise and avoid obesity have lower rates of breast and colon cancer. Prevention of occupationally induced cancers involves minimizing exposure to carcinogenic substances such as asbestos, ionizing radiation, and benzene compounds. Chemoprevention has been widely studied for primary cancer prevention (see above Chemoprevention section and Chapter 39: Cancer). Use of tamoxifen, raloxifene, and aromatase inhibitors for breast cancer prevention is discussed in Chapter 17: Breast Disorders and Chapter 39: Cancer. Hepatitis B vaccination can prevent hepatocellular carcinoma (HCC), and screening and vaccination programs may be cost-effective and useful in preventing HCC in high-risk groups such as Asians and Pacific Islanders. The use of HPV vaccine to prevent cervical cancer is discussed above in the Prevention of Infectious Disease section.

Screening & Early Detection:
Screening has been shown to prevent death from cancers of the breast, colon, and cervix. Current cancer screening recommendations from the American Cancer Society, the Canadian Task Force on Preventive Health Care, and the United States Preventive Services Task Force are shown in Table 1–9.
Cancer screening recommendations for average-risk adults.
Test ACS1
Breast self-examination (BSE) An option for women over age 20. Fair evidence that BSE should not be used.  Insufficient evidence to recommend for or against.  
Clinical breast examination Every 3 years age 20–40 and annually thereafter. Good evidence for annual screening women aged 50-69 by clinical examination and mammography. Insufficient evidence to recommend for or against.  
Mammography Annually age 40 and older. Current evidence does not support the recommendation that screening mammography be included in or excluded from the periodic health examination of women aged 40–49. Recommended every 1–2 years for women aged 40 and over (B).  
Papanicolaou test Annually beginning within 3 years after first vaginal intercourse or no later than age 21. Screening may be done every 2 years with the liquid-based Pap test. Annually at age of first intercourse or by age 18; can move to every-2-year screening after two normal results to age 69. Every 3 years beginning at onset of sexual activity or age 21 (A).  
  After age 30, women with three normal tests may be screened every 2–3 years or every 3 years by Pap test plus the HPV DNA test.       
  Women may choose to stop screening after age 70 if they have had three normal (and no abnormal) results within the last 10 years.   Recommends against routinely screening women older than age 65 if they have had adequate recent screening with normal Pap tests and are not otherwise at high risk for cervical cancer (D).  
Annual stool test for occult blood4 or fecal immunochemical test (FIT)
Screening recommended, with the combination of fecal occult blood test or fecal immunochemical test (FIT) and sigmoidoscopy preferred over stool test or sigmoidoscopy alone. Double-contrast barium enema and colonoscopy also considered reasonable alternatives. Good evidence for screening every 1–2 years over age 50. Screening strongly recommended (A), but insufficient evidence to determine best test.  
Sigmoidoscopy (every 5 years) Fair evidence for screening over age 50 (insufficient evidence about combining stool test and sigmoidoscopy).  
Double-contrast barium enema (every 5 years) Not addressed.  
Colonoscopy (every 10 years) Insufficient evidence for or against use in screening.  
Prostate-specific antigen (PSA) blood test PSA and DRE should be offered annually to men age 50 and older who have at least a 10-year life expectancy. Men at high risk (African American men and men with a strong family history) should begin at age 45. Information should be provided to men about the benefits and risks, and they should be allowed to participate in the decision. Men without a clear preference should be screened. Fair evidence against including in routine care.  Insufficient evidence to recommend for or against.  
Digital Rectal Examination (DRE) Insufficient evidence for or against including in routine care. Insufficient evidence to recommend for or against.  
Cancer-related checkup For people aged 20 or older having periodic health exams, a cancer-related checkup should include counseling and perhaps oral cavity, thyroid, lymph node, or testicular examinations. Not assessed. Not assessed.  

Home test with three samples
Recommendation A: The USPSTF strongly recommends that clinicians routinely provide the service to eligible patients. (The USPSTF found good evidence that the service improves important health outcomes and concludes that benefits substantially outweigh harms.)
Recommendation B: The USPSTF recommends that clinicians routinely provide the service to eligible patients. (The USPSTF found at least fair evidence that the service improves important health outcomes and concludes that benefits substantially outweigh harms.)
Recommendation D: The USPSTF recommends against routinely providing the service to asymptomatic patients. (The USPSTF found at least fair evidence that the service is ineffective or that harms outweigh benefits.)

The appropriate form and frequency of screening for breast cancer is controversial. A large randomized trial of breast self-examination conducted among factory workers in Shanghai found no benefit. A systematic review performed for the United States Preventive Services Task Force found that mammography was moderately effective in reducing breast cancer mortality for women 40–74 years of age. The absolute benefit was greater for older women, and the risk of false-positive results was high for all women. Digital mammography is more sensitive in women with dense breasts and younger women; however, studies exploring outcomes are lacking. Several organizations, including the American Cancer Society and the National Cancer Institute, recommend routine mammography screening, and changes in screening guidelines appear to impact women's beliefs about how frequently they should obtain screening. Although delays to following up an abnormal mammogram exist, the use of patient navigation programs to reduce such delays appears beneficial, especially among poor and minority populations. The use of MRI is not currently recommended for general screening, although the American Cancer Society does recommend screening MRI for women at high risk ( 20–25%), including those with a strong family history of breast or ovarian cancer. A recent systematic review reported that screening with both MRI and mammography might be superior to mammography alone in ruling out cancerous lesions in women with an inherited predisposition to breast cancer.

All current recommendations call for cervical and colorectal cancer screening. Prostate cancer screening, however, is controversial, as no completed studies have answered the question whether early detection and treatment after screen detection produce sufficient benefits to outweigh harms of treatment. A 2008 USPSTF review of current evidence on benefits and harm of screening asymptomatic men for prostate cancer with prostate-specific antigen (PSA) testing revealed that PSA screening is associated with increased psychological harm with uncertain potential benefits. Providers and patients are advised to discuss how to proceed in light of this uncertainty. Whether early detection through screening and subsequent treatment alters the natural course of the disease remains to be seen. There are still no data on the morbidity and mortality benefits of screening. Unlike the American College of Physicians, the American Cancer Society recommends that providers offer annual PSA testing for men over age 50. Screening is not recommended by any group for men who have estimated life expectancies of less than 10 years. Decision aids have been developed to help men weigh the arguments for and against PSA screening.

Annual or biennial fecal occult blood testing reduces mortality from colorectal cancer by 16–33%. The risk of death from colon cancer among patients undergoing at least one sigmoidoscopic examination is reduced by 60–80% compared with that among those not having sigmoidoscopy. Colonoscopy has also been advocated as a screening examination. It is more accurate than flexible sigmoidoscopy for detecting cancer and polyps, but its value in reducing colon cancer mortality has not been studied directly. Recent studies have shown that CT colography (virtual colonoscopy) is also able to detect cancers and polyps with reasonable accuracy.

Screening for cervical cancer with a Papanicolaou smear is indicated in sexually active adolescents and in adult women every 1–3 years. Screening for vaginal cancer with a Papanicolaou smear is not indicated in women who have undergone hysterectomies for benign disease with removal of the cervix—except in diethylstilbestrol (DES)-exposed women (see Chapter 18: Gynecologic Disorders). Women over age 70 who have had normal results on three or more previous Papanicolaou smears may elect to stop screening.
Screening for lung cancer with spiral CT can detect early stage disease; however, its efficacy in reducing lung cancer mortality has not been evaluated in a randomized trial, although a recent study of survival in asymptomatic patients at risk for lung cancer who were screened annually with spiral CT revealed that such screening detected lung cancer at a curable stage.  

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