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. Chemo-prevention has been widely studied for primary cancer prevention. 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 and Early Detection
Screening has been shown to prevent death from cancers of the breast, colon, and cervix. Current cancer screening recommendations from the United States Preventive Services Task Force.
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 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 belief about how frequently they should obtain screening.
Screening for cervical cancer with a Papanicolaou smear is indicated in sexually active adolescents and in adult womens 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 . Women over age 70 who have had normal results on three or more previous Papanicolaou smears may elect to stop screening.
Observational clinical trials have revealed that chest CT is significantly more sensitive that chest radiography in identifying small asymptomatic lung cancers; however, there is no clear evidence that screening for lung cancer reduces mortality. Randomized controlled trials assessing the effect of low-dose CT (LDCT) on lung cancer mortality are underway.
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