Prevention and Early Detection of Cancer¶
Chapter 75 | Harrison's 22e · Part 4 – Oncology: Solid Tumors · Chapter 75
Key Clinical Points¶
- Smoking cessation reduces lung cancer mortality by 30–50% within 10 years.
- Cigar smoking significantly increases risk: 1–2/day doubles oral/esophageal risk; 3–4/day increases oral cancer risk >8-fold.
- Physical activity is associated with reduced colon and breast cancer risks via hormonal, immune, and metabolic mechanisms.
- Low-fat diets have no proven benefit in randomized trials (e.g., Polyp Prevention Trial, Women’s Health Initiative).
- Lung cancer screening via low-dose CT is indicated for high-risk smokers (50–80 years, ≥20 pack-year history, current or quit within 15 years).
- Tobacco prevention is a critical pediatric priority due to high rates of early initiation.
1. EPIDEMIOLOGY & RISK FACTORS¶
Cancer prevention focuses on modifiable risk factors and carcinogenesis pathways.
• Tobacco Impact: ◦ Causes ~1 in 3 premature deaths from tobacco-related diseases ◦ Lung cancer mortality strongly correlated to cigarette consumption and inhalation depth ◦ Environmental tobacco smoke → increased respiratory illness risks in children
• Statistics: ◦ Over 80% of adult smokers began before age 18 ◦ High school boys: smoking declined from 19% (2012) to 7% (2019) ◦ Electronic cigarette use: rose to 20% of high school students in 2020
• Specific Tobacco Types: ◦ Cigar smoking: 1–2 cigars/day → doubles oral/esophageal cancer risk; 3–4 cigars/day → >8-fold oral cancer risk ◦ Smokeless tobacco: linked to oral leukoplakia, dental caries, and esophageal cancer via saliva-soluble carcinogens
• Table 75-1 (Suspected Carcinogens): ◦ Alkylating agents → Acute myeloid leukemia, bladder cancer ◦ Aromatic amines (dyes) → Bladder cancer ◦ Asbestos → Cancer of the lung, pleura, peritoneum ◦ Chromium → Lung cancer ◦ Epstein-Barr virus → Burkitt’s lymphoma, nasal T-cell lymphoma ◦ Ethyl alcohol → Cancer of the breast, liver, esophagus, head and neck ◦ Hepatitis B or C virus → Liver cancer ◦ Human papillomavirus (HPV) → Cancers of the cervix, anus, oropharynx ◦ Immunosuppressive agents (azathioprine, cyclosporine, glucocorticoids) → Non-Hodgkin’s lymphoma ◦ Nitrogen mustard gas → Cancer of the lung, head and neck, nasal sinuses ◦ Diesel exhaust → Lung cancer (miners) ◦ Polycyclic hydrocarbons → Cancer of the lung, skin (especially squamous cell carcinoma of scrotal skin) ◦ Schistosomiasis → Bladder cancer (squamous cell) ◦ Tobacco (including smokeless) → Cancer of the upper aerodigestive tract, bladder, kidney
2. LIFESTYLE MODIFICATIONS FOR CANCER PREVENTION¶
Public health strategies emphasize behavioral interventions and dietary adjustments.
• Physical Activity: ◦ Associated with reduced colon and breast cancer risks ◦ Mechanisms: hormonal changes, immune modulation, and metabolic effects ◦ Confounding factors in studies: recall bias, reverse causality (preclinical cancers affecting exercise), and associations with other healthy behaviors
• Diet Modification: ◦ High-fat diets → correlated with increased breast/colon/prostate cancer risks in ecologic studies ◦ Low-fat diets → not proven to reduce cancer incidence in randomized trials (Polyp Prevention Trial, Women’s Health Initiative) ◦ Fiber intake → no significant association with colorectal cancer prevention in large cohort studies
3. SMOKING CESSATION STRATEGIES¶
Comprehensive cessation programs improve quit rates compared to gradual reduction methods.
• Cessation Interventions: ◦ Effective approaches: counseling, behavioral strategies, nicotine replacement (gum/patches/sprays), bupropion, varenicline ◦ Heavy smokers → require intensive programs with pharmacologic adjuncts ◦ Electronic cigarettes → unproven efficacy and safety profiles due to lack of standardized manufacturing
• Health Impact of Cessation: ◦ Complete cessation → reduces 10-year lung cancer mortality by 30–50% compared to continued smoking ◦ Persistent gene mutations from past smoking do not negate long-term benefits ◦ Tobacco prevention is a pediatric priority given early initiation patterns
4. CLINICAL GUIDANCE FOR PREVENTION¶
Healthcare providers play critical roles in cancer prevention through patient education and screening promotion.
• Provider Recommendations: ◦ Query patients about tobacco use during clinical encounters ◦ Offer cessation assistance or referrals to specialized programs ◦ Counsel on health risks of smoking, diet, and physical activity ◦ Promote evidence-based cancer screening methods
DIAGNOSTIC APPROACH¶
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Evaluation of Diagnostic Test Value (Table 75-2): • Sensitivity: The proportion of persons with the condition who test positive: a / (a + c) • Positive predictive value (PPV): The proportion of persons with a positive test who have the condition: a / (a + b)
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Breast Cancer Screening (Table 75-3): • Self-examination: USPSTF "D"; ACS No specific recommendation • Clinical examination: USPSTF "I" (as a stand-alone without mammography for ≥40 years); ACS Do not recommend • Mammography: ◦ USPSTF: Women 40–74 years → Biennial screening ("B") ◦ ACS: ◦ 40–44 years → Provide opportunity to begin annual screening ◦ 45–54 years → Screen annually ◦ ≥55 years → Transition to biennial or continue annual; continue as long as health is good and life expectancy ≥10 years • Magnetic resonance imaging (MRI): ◦ ACS: ◦ >20% lifetime risk → Screen with MRI plus mammography annually ◦ 15–20% lifetime risk → Discuss option of MRI plus mammography annually ◦ <15% lifetime risk → Do not screen annually with MRI • Pap test (cytology): ◦ USPSTF: ◦ <21 years → "D" ◦ 21–29 years → Cytology alone every 3 years ("A") ◦ 30–65 years → Cytology alone every 3 years OR co-testing (HPV + cytology) every 5 years ("A") ◦ >65 years → "D" (if prior screenings normal) • HPV test: ◦ USPSTF: ◦ <30 years → Do not use for screening ◦ 30–65 years → HPV alone or co-testing every 5 years ("A") ◦ >65 years → "D" (if prior screenings normal)
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Colorectal Cancer Screening (Table 75-3): • USPSTF: ◦ 45–50 years → "B" (Screen for colorectal cancer) ◦ 50–75 years → "A" (Screen for colorectal cancer) ◦ 76–85 years → "C" (Selectively offer based on health/history) • ACS: ◦ ≥45–75 years → Screen with high-sensitivity stool-based test or structural examination ◦ Sigmoidoscopy → Every 5 years ◦ Fecal occult blood testing (FOBT) → Every year ◦ Colonoscopy → Every 10 years ◦ Fecal DNA testing → Every 3 years ◦ Fecal immunochemical testing (FIT) → Every year ◦ Computed tomography (CT) colonography → Every 5 years
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Lung Cancer Screening (Table 75-3): • Low-dose CT scan: ◦ Target: Adults 50–80 years ◦ Criteria: ≥20 pack-year smoking history, currently smoking OR quit within past 15 years ◦ Discontinuation criteria: → If not smoked for 15 years → If health problem limits life expectancy → If health problem limits ability to have curative lung surgery
MANAGEMENT & TREATMENT¶
- Assessment and Counseling: • Query patients about tobacco use during clinical encounters • Counsel on health risks of smoking, diet, and physical activity
- Smoking Cessation Interventions: • Methods: counseling, behavioral strategies, nicotine replacement (gum/patches/sprays), bupropion, varenicline • High-risk patients: Heavy smokers require intensive programs with pharmacologic adjuncts
- Monitoring and Outcomes: • Complete cessation → reduces 10-year lung cancer mortality by 30–50% compared to continued smoking • Note: Persistent gene mutations from past smoking do not negate long-term benefits
KEY PEARLS & HIGH-YIELD POINTS¶
• Tobacco Prevention: A pediatric priority due to high rates of early initiation. • E-Cigarettes: Currently have unproven efficacy and safety profiles due to lack of standardized manufacturing. • Screening Logic: Use of specific tests (e.g., Low-dose CT) is strictly tied to age, smoking history, and duration since quitting.
Reference Tables¶
TABLE 75-1 Suspected Carcinogens CARCINOGENS a Alkylating agents Androgens Aromatic amines (dyes) Arsenic Asbestos…¶
Harrison's 22e, p.512
| CARCINOGENSa | ASSOCIATED CANCER OR NEOPLASM |
|---|---|
| Alkylating agents | Acute myeloid leukemia, bladder cancer |
| Aromatic amines (dyes) | Bladder cancer |
| Asbestos | Cancer of the lung, pleura, peritoneum |
| Chromium | Lung cancer |
| Epstein-Barr virus | Burkitt’s lymphoma, nasal T-cell lymphoma |
| Ethyl alcohol | Cancer of the breast, liver, esophagus, head and neck |
| Hepatitis B or C virus | Liver cancer |
| Human papillomavirus | Cancers of the cervix, anus, oropharynx |
| Immunosuppressive agents (azathioprine, cyclosporine, glucocorticoids) |
Non-Hodgkin’s lymphoma |
| Nitrogen mustard gas | Cancer of the lung, head and neck, nasal sinuses |
| Diesel exhaust | Lung cancer (miners) |
| Polycyclic hydrocarbons | Cancer of the lung, skin (especially squamous cell carcinoma of scrotal skin) |
| Schistosomiasis | Bladder cancer (squamous cell) |
| Tobacco (including smokeless) | Cancer of the upper aerodigestive tract, bladder, kidney |
TABLE 75-2 Assessment of the Value of a Diagnostic Test a Positive test Negative test a = true positive b = false…¶
Harrison's 22e, p.514
| CONDITION PRESENT | CONDITION ABSENT | |
|---|---|---|
| Positive test | a | b |
| c | ||
| a = true positive | ||
| c = false negative | ||
| Sensitivity | The proportion of persons with the condition who test positive: a/(a + c) |
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| Positive predictive value (PPV) | The proportion of persons with a positive test who have the condition: a/(a + b) |
TABLE 75-3 Screening Recommendations for Asymptomatic Subjects Not Known to Be at Increased Risk for the Target…¶
Harrison's 22e, p.516
| CANCER TYPE | TEST OR PROCEDURE | USPSTF | ACS |
|---|---|---|---|
| Breast | Self-examination | “D”b (Not in current recommendations; from 2009) | Women, all ages: No specific recommendation |
| Clinical examination | Women ≥40 years: “I” (as a stand-alone without mammography) (Not in current recommendations; from 2009) |
Women, all ages: Do not recommend | |
| Mammography | Women aged 40-74 years: Biennial screening mammography (“B”) |
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 |
|
| Women ≥75 years: “I” | |||
| Magnetic resonance imaging (MRI) |
“I” | Women with >20% lifetime risk of breast cancer: Screen with MRI plus mammography annually |
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| Women with 15–20% lifetime risk of breast cancer: Discuss option of MRI plus mammography annually |
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| Women with <15% lifetime risk of breast cancer: Do not screen annually with MRI |
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| Pap test (cytology) | Women <21 years: “D” Women 21–29 years: Screen with cytology alone every 3 years (“A”) Women 30–65 years: Screen with cytology alone every 3 years, or with co-testing (HPV testing + cytology) every 5 years (two of three options, see HPV test below) (“A”) Women >65 years, with adequate, normal prior Pap screenings: “D” Women after total hysterectomy for noncancerous causes: “D” |
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| HPV test | Women <30 years: Do not use HPV testing for cervical cancer screening Women 30–65 years: Screen with HPV testing alone or in combination with cytology every 5 years (two of three options, see Pap test above) (“A”) Women >65 years, with adequate, normal prior Pap screenings: “D” Women after total hysterectomy for noncancerous causes: “D” |
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| Colorectal | Overall | Adults 50–75 years: “A” Screen for colorectal cancer Adults 45–50 years: “B” Screen for colorectal cancer Adults 76–85 years: “C” Selectively offer screening for colorectal cancer; consider the patient’s overall health, prior screening history, and preferences |
Adults ≥45–75 years: Screen for colorectal cancer with either a high-sensitivity stool-based test or a structural (visual) examination (≥45 years, qualified recommendation; ≥50 years, strong recommendation). Adults 76–85 years: Individualize screening based on patient preferences, life expectancy, health status, and prior screening history (qualified recommendation). Adults >85 years: Discourage screening (qualified recommendation). Every 5 years |
| Sigmoidoscopy | Every 5 years; modeling suggests improved benefit if performed every 10 years in combination with annual FIT |
Adults ≥45 years: Every 5 years | |
| Fecal occult blood testing (FOBT) |
Every year | Adults ≥45 years: Every year | |
| Colonoscopy | Every 10 years | Adults ≥45 years: Every 10 years | |
| Fecal DNA testing | At least every 3 years | Adults ≥45 years: Every 3 years | |
| Fecal immunochemical testing (FIT) |
Every year | Adults ≥45 years: Every year | |
| Computed tomography (CT) colonography |
Every 5 years | Adults ≥45 years: Every 5 years | |
| Low-dose CT scan | Adults 50–80 years, with a ≥20 pack-year smoking history, still smoking or have quit within past 15 years, annually: “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 |