Prevention and Early Detection of Cancer

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 203-1. 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 203-1: 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 203-2). 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.

TABLE 203-2: SCREENING RECOMMENDATIONS FOR ASYMPTOMATIC SUBJECTS NOT KNOWN TO BE AT INCREASED RISK FOR THE TARGET CONDITIONa
Cancer TypeTest or ProcedureUSPSTFACS
BreastSelf-examination“D”Women ≥20 years: Breast self-exam is an option
Clinical examinationWomen ≥40 years: “I” (as a stand-alone without mammography)

Women 20–39 years: Perform every 3 years

Women ≥40 years: Perform annually

Mammography

Women 40–49 years: The decision should be an individual one, and take pt context/values into account (“C”)

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

Women ≥75 years: “I”

Women ≥40 years: Screen annually for as long as the woman is in good health

Magnetic resonance imaging (MRI)“I”

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

CervicalPap test (cytology)

Women 21–65 years: Screen every 3 years (“A”)

Women <21 years: “D”

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

Women 21–29 years: Screen every 3 years

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: every 5 years in combination with high-sensitivity FOBT every 3 years (“A”)b

Adults 76–85 years: “C”

Adults ≥85 years: “D”

Adults ≥50 years: Screen every 5 years
Fecal occult blood testing (FOBT)

Adults 50–75 years: Annually, for high-sensitivity FOBT (“A”)

Adults 76–85 years: “C”

Adults ≥85 years: “D”

Adults ≥50 years: Screen every year
Colonoscopy

Adults 50–75 years: every 10 years (“A”)

Adults 76–85 years: “C”

Adults ≥85 years: “D”

Adults ≥50 years: Screen every 10 years
Fecal DNA testing“I”Adults ≥50 years: Screen, but interval uncertain
Fecal immuno-chemical testing (FIT)“I”Adults ≥50 years: Screen every year
CT colonography“I”Adults ≥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.

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: “B”

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

“D”

“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 exam
SkinComplete skin examination by clinician or pt“I”Self-examination monthly; clinical exam 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.
  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.
  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.
  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%.

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TY - ELEC T1 - Prevention and Early Detection of Cancer ID - 623131 Y1 - 2017 PB - Harrison's Manual of Medicine UR - https://harrisons.unboundmedicine.com/harrisons/view/Harrisons-Manual-of-Medicine/623131/all/Prevention_and_Early_Detection_of_Cancer ER -