Chapter 208: Prevention and Early Detection of Cancer

Chapter 208: Prevention and Early Detection of Cancer is a topic covered in the Harrison's Manual of Medicine.

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One of the most important functions of medical care is to prevent disease or discover it early enough that treatment might be more effective. All risk factors for cancer have not yet been defined. However, a substantial number of factors that elevate risk are within a person’s control. Some of these factors are listed in Table 208-1. Every physician visit is an opportunity to teach and reinforce the elements of a healthy lifestyle. Cancer screening in the asymptomatic population at average risk is a complex issue. To be of value, screening must detect disease at a stage that is more readily curable than disease that is treated after symptoms appear. For cervix cancer and colon cancer, screening has been shown to save lives. For other tumors, benefit is less clear. Screening can cause harm; complications may ensue from the screening test or the tests done to validate a positive screening test or from treatments for the underlying disease. Furthermore, quality of life can be adversely affected by false-positive tests. Evaluation of screening tools can be biased and needs to rely on prospective randomized studies. Lead-time bias occurs when the natural history of disease is unaffected by the diagnosis, but the pt is diagnosed earlier in the course of disease than normal; thus, the pt spends more of his/her life span knowing the diagnosis. Length bias occurs when slow-growing cancers that might never have come to medical attention are detected during screening. Overdiagnosis is a form of length bias in which a cancer is detected when it is not growing and is not an influence on length of survival. Selection bias is the term for the fact that people who volunteer for screening trials may be different from the general population. Volunteers might have family history concerns that actually elevate their risk, or they may be generally more health-conscious, which can affect outcome.

TABLE 208-1: Lifestyle Factors That Reduce Cancer Risk

Do not use any tobacco products

Maintain a healthy weight; eat a well-balanced dieta; maintain caloric balance

Exercise at least 3 times a week

Prevent sun exposure

Avoid excessive alcohol intake

Practice safe sex; use condoms

aNot precisely defined, but current recommendations include five servings of fruits and vegetables per day, 25 g fiber, and <30% of calories coming from fat.

The various groups that evaluate and recommend screening practice guidelines have used varying criteria to make their recommendations (Table 208-2). The absence of data on survival for a number of diseases has led to a lack of consensus. In particular, four areas are worth noting:

  1. Prostate cancer: Prostate-specific antigen (PSA) levels are elevated in prostate cancer, but a substantial number of the cancers detected appear to be non-life-threatening. PSA screening has not been shown to improve survival. Efforts are underway to develop better tests (predominantly using bound vs. free and rate of increase of PSA) to distinguish lethal and nonlethal cancers. Genetic profiling has not yet provided useful distinctions.
  2. Breast cancer: The data on annual mammography support its use in women age >50 years. However, the benefit for women age 40–49 years is quite small. One study shows some advantage for women who are screened starting at age 40 that appears 15 years later; however, it is unclear if this benefit would not have also been derived by starting screening at age 50 years. Women age 40–49 years have a much lower incidence of breast cancer and a higher false-positive rate on mammography. Nearly half of women screened during their forties will have a false-positive test. Refined methods of screening are in development. Women with familial breast cancer may benefit from MRI screening.
  3. Colon cancer: Annual fecal occult blood testing after age 50 years is felt to be useful. Colonoscopy is the gold standard in colorectal cancer detection, but it is expensive and has not been shown to be cost-effective in asymptomatic people. Commercial tests that combine detection of occult blood and the presence of genetic abnormalities in stool (e.g., Cologuard) have improved upon tests that only detect occult blood in stool.
  4. Lung cancer: Chest radiographs and sputum cytology in smokers appear to identify more early-stage tumors, but paradoxically, the screened pts do not have improved survival. Low-dose spiral CT scanning performed annually for 3 years reduces lung cancer death in older smokers by 20% compared with annual chest x-ray. However, 96% of the positive tests are false-positives and overall survival is improved by only 6.7%.
TABLE 208-2: Screening Recommendations for Asymptomatic Subjects not known to be at Increased Risk for the Target Conditiona
CANCER TYPETEST OR PROCEDUREUSPSTFACS
BreastSelf-examination“D”b (Not in current recommendations; from 2009)Women, all ages: No specific recommendation
 Clinical examinationWomen ≥40 years: “I” (as a stand-alone without mammography) (Not in current recommendations; from 2009)Women, all ages: Do not recommend
 Mammography

Women 40–49 years: The decision to start screening mammography in women prior to age 50 years should be an individual one. Women who place a higher value on the potential benefit than the potential harms may choose to begin biennial screening between the ages of 40 and 49 years. (“C”)

Women 50–74 years: Every 2 years (“B”)

Women ≥75 years: “I”

Women 40–44 years: Provide the opportunity to begin annual screening

Women 45–54 years: Screen annually

Women ≥55 years: Transition to biennial screening or have the opportunity to continue annual screening

Women ≥40 should continue screening mammography as long as their overall health is good and they have a life expectancy of 10 years or longer

 Magnetic resonance imaging (MRI)“I” (Not in current recommendations; from 2009)Women with >20% lifetime risk of breast cancer: Screen with MRI plus mammography annually
   Women with 15–20% lifetime risk of breast cancer: Discuss option of MRI plus mammography annually
   Women with <15% lifetime risk of breast cancer: Do not screen annually with MRI
 TomosynthesisWomen, all ages: “I”No specific recommendation
CervicalPap test (cytology)Women 21–65 years: Screen every 3 years (“A”)Women 21–29 years: Screen every 3 years
  

Women <21 years: “D”

Women >65 years, with adequate, normal prior Pap screenings: “D”

Women 30–65 years: Acceptable approach to screen with cytology every 3 years (see HPV test below)

Women <21 years: No screening

Women >65 years: No screening following adequate negative prior screening

  Women after total hysterectomy for noncancerous causes: “D”Women after total hysterectomy for noncancerous causes: Do not screen
 HPV test

Women 30–65 years: Screen in combination with cytology every 5 years if woman desires to lengthen the screening interval (see Pap test above) (“A”)

Women <30 years: “D”

Women >65 years, with adequate, normal prior Pap screenings: “D”

Women after total hysterectomy for noncancerous causes: “D”

Women 30–65 years: Preferred approach to screen with HPV and cytology co-testing every 5 years (see Pap test above)

Women <30 years: Do not use HPV testing

Women >65 years: No screening following adequate negative prior screening

Women after total hysterectomy for noncancerous causes: Do not screen

ColorectalSigmoidoscopy

Adults, 50–75 years: “A” Screen for colorectal cancer; the risks and benefits of the different screening methods vary

Adults, 76 to 85 years: “C” The decision to screen should be an individual one, taking into account the pt’s overall health and prior screening history

Every 5 years; modeling suggests improved benefit if performed every 10 years in combination with annual FIT

Adults ≥50 years: Screen every 5 years
 Fecal occult blood testing (FOBT)Every yearAdults ≥50 years: Screen every year
 ColonoscopyEvery 10 yearsAdults ≥50 years: Screen every 10 years
 Fecal DNA testingEvery 1 or 3 yearsAdults ≥50 years: Screen, but interval uncertain
 Fecal immuno-chemical testing (FIT)Every yearAdults ≥50 years: Screen every year
 CT colonographyEvery 5 yearsAdults ≥50 years: Screen every 5 years
LungLow-dose computed tomography (CT) scan

Adults 55–80 years, with a ≥30 pack-year smoking history, still smoking or have quit within past 15 years: “B”

Discontinue once a person has not smoked for 15 years or develops a health problem that substantially limits life expectancy or the ability to have curative lung surgery

Men and women, 55–74 years, with ≥30 pack-year smoking history, still smoking or have quit within past 15 years: Discuss benefits, limitations, and potential harms of screening; only perform screening in facilities with the right type of CT scanner and with high expertise/specialists
Ovarian

CA-125

Transvaginal ultrasound

Women, all ages: “D”

Women, all ages: “D”

There is no sufficiently accurate test proven effective in the early detection of ovarian cancer. For women at high risk of ovarian cancer and/or who have unexplained, persistent symptoms, the combination of CA-125 and transvaginal ultrasound with pelvic exam may be offered
ProstateProstate-specific antigen (PSA)Men, all ages: “D”Starting at age 50, men should talk to a doctor about the pros and cons of testing so they can decide if testing is the right choice for them. If African American or have a father or brother who had prostate cancer before age 65, men should have this talk starting at age 45. How often they are tested will depend on their PSA level
 Digital rectal examination (DRE)No individual recommendationAs for PSA; if men decide to be tested, they should have the PSA blood test with or without a rectal examination
SkinComplete skin examination by clinician or ptAdults, all ages: “I”Self-examination monthly; clinical examination as part of routine cancer-related checkup
aSummary of the screening procedures recommended for the general population by the USPSTF and the ACS. These recommendations refer to asymptomatic persons who are not known to have risk factors, other than age or gender, for the targeted condition.
bUSPSTF lettered recommendations are defined as follows: “A”: The USPSTF recommends the service, because there is high certainty that the net benefit is substantial; “B”: The USPSTF recommends the service, because there is high certainty that the net benefit is moderate or moderate certainty that the net benefit is moderate to substantial; “C”: The USPSTF recommends selectively offering or providing this service to individual pts based on professional judgment and pt preferences; there is at least moderate certainty that the net benefit is small; “D”: The USPSTF recommends against the service because there is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits; “I”: The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of the service.
Abbreviations: ACS, American Cancer Society; USPSTF, U.S. Preventive Services Task Force.

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