Care Continuum · 5 min read
Epidemiology and Risk Factors · Screening and Early Detection
Core Epidemiologic Terms
Epidemiology describes how cancer is distributed in populations and which factors influence risk. Nurses use these terms to interpret screening data, explain risk to patients and read research.
| Term | Meaning |
|---|---|
| Incidence | New cases in a population over a set period |
| Prevalence | All existing cases (new and old) at a point in time |
| Mortality rate | Deaths from the cancer over a set period |
| Relative risk | Risk in exposed ÷ risk in unexposed |
| Sensitivity | Ability of a test to identify those WITH disease (true positives) |
| Specificity | Ability of a test to identify those WITHOUT disease (true negatives) |
| Lead-time bias | Earlier detection appears to lengthen survival without delaying death |
| Overdiagnosis | Detection of indolent cancer that would never have caused harm |
Cancer is the second leading cause of death in the United States. Excluding skin cancers, breast cancer is the most commonly diagnosed cancer in women and prostate cancer in men, while lung cancer remains the leading cause of cancer death in both sexes. Incidence rises steeply with age, which is why age is the strongest single risk factor for most cancers.
Modifiable and Non-modifiable Risk Factors
Occupational and environmental exposures are modifiable through engineering controls, PPE and regulation. Nurses taking a health history should ask about work history, military service and home exposures such as radon.
| Exposure | Associated cancer(s) |
|---|---|
| Asbestos | Mesothelioma, lung (synergistic with smoking) |
| Radon | Lung (leading cause in never-smokers) |
| Benzene | Acute myeloid leukemia |
| Vinyl chloride | Hepatic angiosarcoma |
| Aromatic amines, dyes | Bladder |
| Ionizing radiation | Leukemia, thyroid, breast, sarcoma |
| EBV | Nasopharyngeal, Burkitt and Hodgkin lymphoma |
| HHV-8 | Kaposi sarcoma |
| HPV | Cervical, oropharyngeal, anal, genital |
| HBV / HCV | Hepatocellular carcinoma (HCV also NHL) |
- Age is the strongest non-modifiable risk factor for most cancers.
- Lung cancer is the leading cause of cancer death; breast (women) and prostate (men) are the most common diagnoses.
- Sensitivity = correctly identifies disease; specificity = correctly identifies absence of disease.
- Radon is the leading cause of lung cancer in never-smokers; asbestos causes mesothelioma; benzene causes AML.
- Lead-time bias and overdiagnosis can make screening look more beneficial than it is.
Principles of Screening
Screening (secondary prevention) tests asymptomatic people to find cancer or precancer early. A worthwhile screening program targets a common cancer with a detectable preclinical phase, uses an acceptable test with good sensitivity and specificity, and has evidence that early treatment reduces mortality. Harms include false positives, anxiety, invasive follow-up procedures, radiation exposure and overdiagnosis. Symptomatic patients need diagnostic evaluation, not screening.
Average-Risk Screening Recommendations
The table summarizes current U.S. Preventive Services Task Force (USPSTF) recommendations with key American Cancer Society (ACS) differences. Recommendations apply to average-risk, asymptomatic adults; higher-risk individuals follow enhanced protocols.
| Cancer | Current USPSTF | Key ACS differences |
|---|---|---|
| Breast | Mammography every 2 years, ages 40–74 | Option at 40–44; annual 45–54; then every 1–2 years while life expectancy is 10+ years |
| Cervical | 21–29: cytology every 3 years. 30–65: primary hrHPV every 5 years, cotest every 5 years, or cytology every 3 years | Begin at 25 with primary HPV every 5 years (preferred) through 65 |
| Colorectal | Ages 45–75; 76–85 individualized | Same start at 45; not recommended after 85 |
| Lung | Annual LDCT, ages 50–80, 20+ pack-years, currently smoke or quit within 15 years | Former smokers eligible regardless of years since quitting |
| Prostate | 55–69: individual decision about PSA; 70+: do not screen | Shared decision at 50; at 45 for Black men or first-degree relative diagnosed before 65; at 40 if higher risk |
Colorectal Screening Options
| Test | Interval | Note |
|---|---|---|
| Colonoscopy | Every 10 years | Diagnostic and therapeutic (polyp removal) |
| FIT (fecal immunochemical test) | Every year | No diet or drug restrictions |
| Multitarget stool DNA (sDNA-FIT) | Every 1–3 years | Higher sensitivity, more false positives |
| CT colonography | Every 5 years | Abnormal result requires colonoscopy |
| Flexible sigmoidoscopy | Every 5 years (or 10 with annual FIT) | Examines distal colon only |
Any positive stool-based or CT colonography result must be followed by colonoscopy; the screening is not complete until that follow-up occurs. Patients with a first-degree relative diagnosed with colorectal cancer before 60, inflammatory bowel disease, Lynch syndrome or FAP start earlier and are screened by colonoscopy.
Other Cancers and High-Risk Surveillance
There is no recommended population screening for ovarian, pancreatic, testicular, thyroid or skin cancer in average-risk adults; the USPSTF recommends against ovarian cancer screening in average-risk women. Targeted surveillance is used in high-risk groups: ultrasound with or without AFP every 6 months for hepatocellular carcinoma in cirrhosis or chronic hepatitis B; annual breast MRI plus mammography for BRCA carriers and women who received chest radiation before age 30; and endometrial biopsy consideration for Lynch syndrome. Women at menopause should be taught to report any postmenopausal bleeding promptly.
Nurses promote screening by identifying eligible patients, explaining benefits and limitations, facilitating shared decision-making (required for lung screening and recommended for PSA), addressing barriers (cost, transportation, fear, language) and ensuring abnormal results are followed up.
- Breast (USPSTF): biennial mammography, ages 40–74.
- Cervical: start at 21 (USPSTF); ages 30–65 primary hrHPV every 5 years; stop after 65 with adequate negative history; no screening after total hysterectomy for benign disease.
- Colorectal: begin at 45; colonoscopy every 10 years or FIT yearly; any positive noninvasive test requires colonoscopy.
- Lung: annual LDCT, ages 50–80, 20+ pack-years, currently smoking or quit within 15 years.
- Prostate: PSA screening is an individual, shared decision at 55–69 (USPSTF); earlier discussion for Black men and those with family history.
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