Primary Prevention
Cancer mortality rates continue to decrease in the United States; part of this decrease results from reductions in tobacco use, since cigarette smoking is the most important preventable cause of cancer. 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). Use of tamoxifen, raloxifene, and aromatase inhibitors for breast cancer prevention is discussed in Chapters 17 and 39. Hepatitis B vaccination can prevent hepatocellular carcinoma (HCC), and screening and vaccination programs may be costeffective 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 prevents death from cancers of the breast, colon, and cervix. Current cancer screening recommendations from the USPSTF are shown in Table 1–6.
Evidence suggests that the benefit of screening mammography on breast cancer mortality may not outweigh the risks associated with screening. A 2011 Cochrane review estimated that screening with mammography led to a reduction in breast cancer mortality of 15% but resulted in 30% overdiagnosis and overtreatment. Currently, the appropriate form and frequency of screening for breast cancer remains controversial and screening guidelines vary. In 2009, the USPSTF updated its recommendation statement on breast cancer screening in the general population. A change, which generated discussion from many groups, was the recommendation against routine screening mammography in women aged 40–49 years. Clinicians should discuss the risks and benefits with each patient and consider individual patient preferences when deciding when to begin screening.
Digital mammography is more sensitive in women with dense breasts and younger women; however, studies exploring outcomes are lacking. 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 2008 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. Screening for testicular cancers among asymptomatic adolescent or adult males is not recommended by the USPSTF. 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 2009 published study of 76,000 US men comparing annual screening (prostatespecific antigen [PSA] and digital rectal examination) to usual care did not reveal a difference in mortality. A 2011 Cochrane systematic review revealed that prostate cancer screening with PSA testing did not significantly decrease either all cause or prostate cancer–specific mortality in men aged 50–74 years. Furthermore, it appeared that any benefits from screening would take more than 10 years to accrue, and screening men with less than 10–15 years life expectancy was not advised.
Annual or biennial fecal occult blood testing reduces mortality from colorectal cancer by 16–33%. Immunochemical fecal occult blood tests (FIT) are superior to guaiac-based fecal occult blood tests (FOBT) in detecting advanced adenomatous polyps and colorectal cancer, and patients are more likely to favor FIT over FOBTs. 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. CT colonography (virtual colonoscopy) is a noninvasive option in screening for colorectal cancer. It has been shown to have a high safety profile and performance similar to colonoscopy.
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). Women over age 70 who have had normal results on three or more previous Papanicolaou smears may elect to stop screening.
In a randomized, controlled trial, transvaginal ultrasound combined with serum cancer antigen 125 (CA-125) as screening tools to detect ovarian cancer did not reduce mortality. Furthermore, complications were associated with diagnostic evaluations to follow up false-positive screening test results. Thus, screening for ovarian cancer with transvaginal ultrasound and CA-125 is not recommended.
Evidence suggests that chest CT is significantly more sensitive that chest radiography in identifying small asymptomatic lung cancers. The National Lung Screening Trial (NLST), a randomized clinical trial of over 53,000 individuals at high risk for lung cancer, revealed a 20% relative reduction and 6.7% absolute reduction in lung cancer mortality in those who were screened with annual lowdose CTs for 3 years compared with those who had chest radiographs. There were a greater number of false-positive results in the low-dose CT group compared with those in the radiography group (23.3% vs 6.5%).
Evidence suggests that the benefit of screening mammography on breast cancer mortality may not outweigh the risks associated with screening. A 2011 Cochrane review estimated that screening with mammography led to a reduction in breast cancer mortality of 15% but resulted in 30% overdiagnosis and overtreatment. Currently, the appropriate form and frequency of screening for breast cancer remains controversial and screening guidelines vary. In 2009, the USPSTF updated its recommendation statement on breast cancer screening in the general population. A change, which generated discussion from many groups, was the recommendation against routine screening mammography in women aged 40–49 years. Clinicians should discuss the risks and benefits with each patient and consider individual patient preferences when deciding when to begin screening.
Digital mammography is more sensitive in women with dense breasts and younger women; however, studies exploring outcomes are lacking. 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 2008 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. Screening for testicular cancers among asymptomatic adolescent or adult males is not recommended by the USPSTF. 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 2009 published study of 76,000 US men comparing annual screening (prostatespecific antigen [PSA] and digital rectal examination) to usual care did not reveal a difference in mortality. A 2011 Cochrane systematic review revealed that prostate cancer screening with PSA testing did not significantly decrease either all cause or prostate cancer–specific mortality in men aged 50–74 years. Furthermore, it appeared that any benefits from screening would take more than 10 years to accrue, and screening men with less than 10–15 years life expectancy was not advised.
Annual or biennial fecal occult blood testing reduces mortality from colorectal cancer by 16–33%. Immunochemical fecal occult blood tests (FIT) are superior to guaiac-based fecal occult blood tests (FOBT) in detecting advanced adenomatous polyps and colorectal cancer, and patients are more likely to favor FIT over FOBTs. 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. CT colonography (virtual colonoscopy) is a noninvasive option in screening for colorectal cancer. It has been shown to have a high safety profile and performance similar to colonoscopy.
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). Women over age 70 who have had normal results on three or more previous Papanicolaou smears may elect to stop screening.
In a randomized, controlled trial, transvaginal ultrasound combined with serum cancer antigen 125 (CA-125) as screening tools to detect ovarian cancer did not reduce mortality. Furthermore, complications were associated with diagnostic evaluations to follow up false-positive screening test results. Thus, screening for ovarian cancer with transvaginal ultrasound and CA-125 is not recommended.
Evidence suggests that chest CT is significantly more sensitive that chest radiography in identifying small asymptomatic lung cancers. The National Lung Screening Trial (NLST), a randomized clinical trial of over 53,000 individuals at high risk for lung cancer, revealed a 20% relative reduction and 6.7% absolute reduction in lung cancer mortality in those who were screened with annual lowdose CTs for 3 years compared with those who had chest radiographs. There were a greater number of false-positive results in the low-dose CT group compared with those in the radiography group (23.3% vs 6.5%).
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