Blood Testing for Cancer Screening in Asymptomatic Average-Risk Adults
Routine blood testing is not recommended for cancer screening in asymptomatic, average-risk adults. Current evidence-based guidelines support only site-specific screening methods (stool-based tests, endoscopy, and imaging) for colorectal cancer, mammography for breast cancer, and Pap/HPV testing for cervical cancer—none of which are blood tests 1.
Why Blood Tests Are Not Recommended
Blood-based tumor biomarkers lack the reliability and validation necessary for screening asymptomatic individuals 2. While research continues on developing multi-analyte blood tests that could detect multiple cancer types simultaneously, these remain investigational and are not part of any established screening guideline 3.
The absence of blood tests from all major cancer screening guidelines reflects the lack of evidence that they reduce cancer-specific mortality or improve quality of life in average-risk populations.
Evidence-Based Cancer Screening for Average-Risk Adults
Instead of blood tests, guidelines recommend the following site-specific screening strategies:
Colorectal Cancer Screening
Begin screening at age 50 years (or age 45 per some guidelines) and continue through age 75 years 1.
First-tier screening options include:
- Fecal immunochemical test (FIT) annually 1, 4
- High-sensitivity guaiac-based fecal occult blood test (gFOBT) every 2 years 1
- Colonoscopy every 10 years 1, 5
- Flexible sigmoidoscopy every 10 years plus FIT every 2 years 1
These stool-based and endoscopic tests have demonstrated reduction in colorectal cancer-specific mortality in randomized controlled trials, though none have shown reduction in all-cause mortality 1.
Discontinue screening after age 75 years or when life expectancy is less than 10 years, as harms outweigh benefits in these populations 1.
Breast Cancer Screening
Begin annual mammography at age 40 years and continue while the woman remains in good health 1, 6.
Clinical breast examination should be performed every 3 years for women ages 20-39 and annually after age 40 1, 6.
Cervical Cancer Screening
Begin screening at age 21 years 1, 6.
- Ages 21-29: Pap test every 3 years 1, 6
- Ages 30-65: Pap test plus HPV co-testing every 5 years (preferred) or Pap test alone every 3 years 1, 6
- Discontinue after age 65 with adequate prior negative screening 1, 6
Prostate Cancer Screening
Offer PSA testing and digital rectal examination starting at age 50 years only after shared decision-making discussion in men with at least 10-year life expectancy 1, 6. This is a conditional recommendation due to uncertain balance of benefits and harms 6.
Critical Implementation Points
All positive stool-based tests require prompt follow-up colonoscopy—the screening process is only effective when completed 1, 4.
Screening adherence is essential: One-time or sporadic testing has very limited sensitivity and undermines the effectiveness of any screening strategy 4.
Patient preference matters: Select the screening test through shared decision-making that considers benefits, harms, costs, availability, frequency, and individual values 1.
Common Pitfalls to Avoid
Do not order tumor markers (CEA, CA 19-9, CA-125, PSA without discussion) as general cancer screening tests in asymptomatic patients—they lack validation for this purpose and lead to false positives, unnecessary anxiety, and costly workups 2.
Do not continue screening beyond recommended age limits or in patients with limited life expectancy, as the time required to realize mortality benefit (approximately 10 years for colorectal cancer) exceeds their remaining lifespan 1.
Do not assume that any single screening test is superior—multiple modalities have proven mortality benefit for colorectal cancer, and the best test is the one the patient will actually complete 1, 7.