Prevention and Early Detection of Cancer¶
Chapter 75 | Part 4: Oncology and Hematology
KEY CLINICAL POINTS¶
- Smoking cessation is the most effective modifiable risk factor for cancer prevention, with nicotine replacement therapy, bupropion, and varenicline as key pharmacologic aids.
- Chemoprevention agents like tamoxifen, raloxifene, and aromatase inhibitors reduce breast cancer risk but carry risks of side effects and overdiagnosis.
- HPV vaccination prevents ~70% of cervical cancers and is recommended for both males and females (nonavalent vaccine covering strains 6, 11, 16, 18, 31, 33, 45, 52, 58).
- Screening for cervical, colorectal, and breast cancers reduces mortality, but overdiagnosis and false positives remain significant challenges.
- Lung cancer screening with low-dose CT in high-risk individuals reduces mortality by ~20%, while PSA screening for prostate cancer has limited impact on mortality.
1. DEFINITION & OVERVIEW¶
Cancer prevention involves reducing exposure to carcinogens and modifying risk factors to prevent cancer initiation, promotion, and progression. Early detection focuses on identifying cancer at asymptomatic stages to improve outcomes. Chemoprevention uses agents to reverse or suppress carcinogenesis before malignancy develops.
Table 75-1 Suspected Carcinogens¶
| CARCINOGENsa | ASSOCIATED CANCER OR NEOPLASM |
|---|---|
| Alkylating agents | Acute myeloid leukemia, bladder cancer |
| Androgens | Prostate cancer |
| Aromatic amines (dyes) | Bladder cancer |
| Arsenic | Lung, skin cancer |
| Asbestos | Lung, pleura, peritoneum cancer |
| Benzene | Acute myelocytic leukemia |
| Chromium | Lung cancer |
| Diethylstilbestrol (prenatal) | Vaginal cancer (clear cell) |
| Epstein-Barr virus | Burkitt’s lymphoma, nasal T-cell lymphoma |
| Estrogens | Endometrium, liver, breast cancer |
| Ethyl alcohol | Breast, liver, esophagus, head and neck cancer |
| Helicobacter pylori | Gastric cancer, gastric MALT lymphoma |
| CARCINOGENsa | ASSOCIATED CANCER OR NEOPLASM |
|---|---|
| Hepatitis B or C virus | Liver cancer |
| Human immunodeficiency virus | Non-Hodgkin’s lymphoma, Kaposi’s sarcoma, squamous cell carcinomas |
| Human papillomavirus | Cervix, anus, oropharynx cancer |
| Human T-cell lymphotropic virus | Adult T-cell leukemia/lymphoma |
| Immunosuppressive agents | Non-Hodgkin’s lymphoma |
| Ionizing radiation | Breast, bladder, thyroid, soft tissue, bone, hematopoietic, and many more cancers |
| Nitrogen mustard gas | Lung, head and neck, nasal sinus cancer |
| Nickel dust | Lung, nasal sinus cancer |
| Diesel exhaust | Lung cancer (miners) |
| Phenacetin | Renal pelvis and bladder cancer |
| Polycyclic hydrocarbons | Lung, skin (especially squamous cell carcinoma of scrotal skin) |
| Radon gas | Lung cancer |
| Schistosomiasis | Bladder cancer (squamous cell) |
| Sunlight (ultraviolet) | Skin cancer (squamous cell and likely melanoma) |
| Tobacco (including smokeless) | Upper aerodigestive tract, bladder, kidney cancer |
| Vinyl chloride | Liver cancer (angiosarcoma) |
1.1 Carcinogenesis Process¶
Carcinogenesis is a multi-step process involving initiation (genetic mutations), promotion (tumor growth), and progression (metastasis). Environmental, genetic, and lifestyle factors interact to drive this process.
1.2 Prevention Strategies¶
Primary prevention targets carcinogen exposure (e.g., tobacco, UV radiation), while secondary prevention focuses on early detection through screening. Lifestyle modifications (diet, exercise) and vaccines (e.g., HPV) are critical components.
2. EPIDEMIOLOGY¶
Cancer incidence is influenced by age, gender, and lifestyle factors. Tobacco use is the leading preventable cause of cancer mortality, with smoking contributing to ~20% of all cancer deaths. Obesity and physical inactivity are linked to increased risks for colon, breast, and endometrial cancers.
2.1 Risk Factors¶
Key risk factors include tobacco use (smoking, smokeless tobacco), obesity, alcohol consumption, UV radiation exposure, and infectious agents (e.g., HPV, H. pylori). Genetic predisposition (e.g., BRCA1/2 mutations) increases risks for breast, ovarian, and pancreatic cancers.
2.2 Demographics¶
Incidence rises with age, with most cancers diagnosed in individuals over 55 years. Men are more likely to develop lung, bladder, and prostate cancers, while women are at higher risk for breast, cervical, and ovarian cancers.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Cancer arises from interactions between genetic susceptibility and environmental carcinogens. Carcinogens induce DNA mutations, disrupt cell cycle regulation, and promote angiogenesis and metastasis. Hormonal factors (e.g., estrogen, androgens) and chronic inflammation also contribute to tumor development.
3.1 Carcinogen Types¶
Carcinogens include physical agents (ionizing radiation), chemical agents (asbestos, benzene), and biological agents (HPV, H. pylori). These agents can act as initiators, promoters, or both in the carcinogenic process.
3.2 Hormonal Influences¶
Estrogen and androgen excess are linked to breast, endometrial, and prostate cancers. Hormonal therapies (e.g., aromatase inhibitors) modulate these risks but require careful monitoring for side effects.
4. CLINICAL FEATURES¶
Early-stage cancers may be asymptomatic, but advanced disease presents with localized symptoms (e.g., weight loss, fatigue) or metastatic signs (e.g., lymphadenopathy, organ dysfunction). Screening is critical for asymptomatic individuals at high risk.
4.1 Symptomatology¶
Common symptoms include unexplained weight loss, fatigue, changes in bowel/bladder habits, and persistent pain. Early detection relies on screening rather than symptoms.
4.2 Complications¶
Late-stage cancers may cause cachexia, metastasis, and organ failure. Overdiagnosis and overtreatment are risks of screening programs.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnoses include benign lesions (e.g., hyperplasia, fibroadenoma), infections (e.g., tuberculosis, fungal infections), and non-neoplastic conditions (e.g., inflammatory bowel disease, hormonal disorders).
5.1 Benign vs. Malignant Lesions¶
Differentiation relies on imaging features (e.g., size, margins), biomarkers (e.g., CA-125, PSA), and histopathology. Overlapping features may require follow-up or biopsy.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic tools include imaging (CT, MRI, PET), endoscopy, and biomarker testing. Screening programs use age-specific protocols (e.g., mammography, colonoscopy) to detect cancers at early stages.
Table 75-2 Assessment of the Value of a Diagnostic Testa¶
| CONDITION PRESENT | CONDITION ABSENT | Positive test | Negative test |
|---|---|---|---|
| a | b | c | d |
| Sensitivity | The proportion of persons with the condition who test positive: a/(a + c) | Specificity | The proportion of persons without the condition who test negative: d/(b + d) |
| Positive predictive value (PPV) | The proportion of persons with a positive test who have the condition: a/(a + b) | Negative predictive value | The proportion of persons with a negative test who do not have the condition: d/(c + d) |
6.1 Screening Modalities¶
Recommended screening includes: mammography (breast), Pap smear (cervix), colonoscopy (colorectal), and low-dose CT (lung). Stool-based tests (FIT, FIT-DNA) are alternatives for colorectal cancer.
6.2 Diagnostic Accuracy¶
Screening test performance is evaluated using sensitivity, specificity, and predictive values. Lead-time bias and overdiagnosis may inflate apparent survival rates.
7. MANAGEMENT & TREATMENT¶
Management includes chemoprevention (e.g., tamoxifen, aspirin), lifestyle modifications, and screening. Treatment depends on cancer type, stage, and patient comorbidities.
Table 75-3 Screening Recommendations for Asymptomatic Subjects Not Known to Be at Increased Risk for the Target Conditiona¶
| CANCER TYPE | TEST OR PROCEDURE | USPSTF | ACS |
|---|---|---|---|
| Breast | Self-examination | D | No specific recommendation |
| Breast | Clinical examination | I | Do not recommend |
| Breast | Mammography | B | Provide opportunity to begin annual screening |
| Breast | Magnetic resonance imaging (MRI) | I | Screen with MRI plus mammography annually for >20% lifetime risk |
| Cervical | Pap test (cytology) | A | Screen every 3 years for 21–29 years |
| Cervical | HPV test | A | Screen with HPV testing alone or in combination with cytology every 5 years |
| Colorectal | Colonoscopy | A | Every 10 years for ‡45 years |
| Colorectal | Fecal immunochemical testing (FIT) | A | Every year for ‡45 years |
| Lung | Low-dose CT scan | B | Annual for 50–80 years with ‡20 pack-year smoking history |
| Prostate | Prostate-specific antigen (PSA) | C | Individual decision with clinician discussion |
| CANCER TYPE | TEST OR PROCEDURE | USPSTF | ACS |
|---|---|---|---|
| Skin | Complete skin examination | I | No guidelines |
7.1 Chemoprevention Agents¶
Tamoxifen and raloxifene reduce breast cancer risk but increase thromboembolic events. Aspirin and NSAIDs may lower colorectal cancer risk but carry bleeding risks. Aromatase inhibitors (e.g., anastrozole) are preferred for postmenopausal women.
7.2 Screening Protocols¶
Screening guidelines vary by cancer type: mammography (breast), Pap smear (cervix), colonoscopy (colorectal), and low-dose CT (lung). Recommendations are based on age, risk factors, and population studies.
8. PROGNOSIS & COMPLICATIONS¶
Early detection improves survival rates, but overdiagnosis and overtreatment remain challenges. Prostate cancer screening may lead to unnecessary interventions, while lung cancer screening reduces mortality in high-risk groups.
8.1 Survival Rates¶
Five-year survival rates vary by cancer type: 90% for early-stage breast cancer vs. 15% for metastatic lung cancer. Screening reduces mortality but may not alter overall survival.
8.2 Overdiagnosis¶
Screening detects many asymptomatic cancers, but some may never progress. Overdiagnosis leads to unnecessary treatments and anxiety, particularly in prostate and breast cancers.
9. SPECIAL CONSIDERATIONS¶
Pregnancy, pediatric, and elderly populations require tailored approaches. For example, HPV vaccination is recommended for adolescents, while elderly patients may benefit from less invasive screening protocols.
9.1 Pregnancy and Breastfeeding¶
Radiation and certain chemotherapies are contraindicated during pregnancy. Breastfeeding may reduce breast cancer risk but requires careful management of medications.
9.2 Pediatric Considerations¶
Childhood cancers (e.g., leukemia, lymphoma) are rare but require prompt diagnosis. Preventive measures like HPV vaccination are critical in adolescents.
10. KEY POINTS & CLINICAL PEARLS¶
- Smoking cessation is the most effective cancer prevention strategy. 2. HPV vaccination prevents ~70% of cervical cancers. 3. Mammography reduces breast cancer mortality in women ≥ 50 years. 4. Colonoscopy is the most effective colorectal cancer screening method. 5. PSA screening for prostate cancer has limited impact on mortality and carries risks of overdiagnosis.