Cumulative Prevalence Calculation for Colon Cancer
The cumulative prevalence is 0.375% (Option A), calculated by adding new cases (300) plus existing cases (75) divided by the total population (100,000), which equals 375 per 100,000 or 0.375%.
Understanding the Calculation
Cumulative prevalence represents the total burden of disease in a population at a specific point in time, including both new and pre-existing cases.
- Cumulative prevalence = (New cases + Existing cases) / Total population × 100
- In this scenario: (300 + 75) / 100,000 × 100 = 0.375%
Why This Matters Clinically
- This prevalence rate of 0.375% (375 per 100,000) aligns with contemporary colorectal cancer burden data, where age-standardized incidence rates range from approximately 30-45 per 100,000 in most populations 1
- The cumulative prevalence accounts for both incident cases (new diagnoses) and prevalent cases (existing survivors), which is critical for healthcare resource planning 2
- Global estimates indicate colorectal cancer represents approximately 10% of all tumor types worldwide, with cumulative risk of onset between 0-74 years being approximately 2.27% 3, 2
Common Pitfalls to Avoid
- Do not confuse prevalence with incidence: Incidence only counts new cases, while prevalence includes all existing cases in the population
- Do not express as "per 1000": Options C and D are incorrect because 0.375 per 1000 would equal 0.0375%, which is 10-fold lower than the correct answer
- Do not use only new cases: The 300 new cases alone would give incidence (0.3%), not cumulative prevalence
Clinical Context
- Colorectal cancer is the third most common cancer worldwide and second leading cause of cancer death 1, 3
- Understanding prevalence versus incidence is essential for distinguishing screening needs (which target incident disease) from treatment burden (which reflects prevalent disease) 1
- The mortality-to-incidence ratio globally stands at approximately 0.48, indicating that roughly half of diagnosed patients will die from the disease, emphasizing the importance of early detection 4