Why are most tumor markers not used to screen the general population?

• A. cannot be inexpensively quantified.
• B. can also be elevated in conditions other than the cancer.
• C. do not rise to high enough levels in presence of cancer.
• D. vary too much between patients belonging to different ethnic populations.

Answer: (B)

Tumor markers are not specific to cancer; they can go up in a range of non-cancer conditions. For screening the general population, you need a test with high specificity, because the population prevalence of cancer is low. If a marker can be elevated in benign or inflammatory states, many healthy people would test positive, leading to false positives and unnecessary follow-up procedures, anxiety, and potential harms, while still missing cancers in those who don’t have a pronounced marker elevation. That’s why these markers are not suitable for population screening.

For context, PSA can be raised by benign prostatic hyperplasia or prostatitis; CA-125 can be elevated with endometriosis, fibroids, or pregnancy; CEA can be higher in smokers or inflammatory conditions; CA 19-9 can rise with pancreatitis or biliary obstruction. The key issue is lack of cancer-specificity, not cost, the absolute level rise, or differences among ethnic groups.