Blood Tests for Cancer: Diagnosis & Screening
Discover how blood tests help detect, diagnose, and monitor cancer, and learn about the latest advances in multi-cancer screening.
What Are Blood Tests for Cancer?
Blood tests play a crucial role in the diagnosis, monitoring, and screening of cancer. While not all cancers can be detected through blood work, certain types—especially blood cancers—can be identified by analyzing blood cell counts and specific tumor markers. Blood tests are also used to monitor cancer progression and response to treatment.
Types of Blood Tests Used in Cancer Diagnosis
Several types of blood tests are used to help diagnose and monitor cancer. These include:
- Complete Blood Count (CBC): Measures red and white blood cells and platelets. Abnormal levels may indicate blood cancers like leukemia or lymphoma.
- Tumor Marker Tests: Detect substances produced by cancer cells or by the body in response to cancer. Examples include alpha-fetoprotein (AFP) for liver cancer, CA-125 for ovarian cancer, and calcitonin for thyroid cancer.
- Circulating Tumor DNA (ctDNA) Tests: Look for DNA fragments shed by cancer cells into the bloodstream. These are used to monitor certain cancers and are being developed for early detection.
Can Blood Tests Detect All Types of Cancer?
No, blood tests alone cannot detect all types of cancer. While they are effective for blood cancers and some solid tumors, most solid organ cancers (like lung, breast, or colon cancer) are not reliably detected by routine blood tests. In these cases, imaging tests and tissue biopsies are necessary for diagnosis.
Limitations of Blood Tests for Cancer
It is possible to have cancer even with normal blood test results. Blood work is just one tool in cancer diagnosis and should be combined with other tests such as imaging and biopsies. Additionally, some cancers do not shed enough DNA or produce detectable markers in the blood, making them harder to identify with current blood tests.
Multi-Cancer Early Detection (MCED) Tests
Recent advances have led to the development of multi-cancer early detection (MCED) tests, such as the Galleri test. These tests can detect more than 50 types of cancer from a single blood draw by analyzing cell-free DNA (cfDNA) and methylation patterns. MCED tests are particularly effective at identifying cancers that are often diagnosed at later stages, such as pancreatic and ovarian cancer.
How Do MCED Tests Work?
MCED tests work by identifying DNA that cancerous tumors shed into the blood, known as cell-free DNA (cfDNA). The test analyzes chemical changes to the DNA called “methylation” that control gene expression. Abnormal methylation patterns can indicate the presence of cancer and help identify the tissue of origin.
Accuracy and False Positives
MCED tests have shown high accuracy in detecting cancer signals and identifying the likely organ of origin. For example, the Galleri test has a false-positive rate of about 0.5%, meaning it is highly accurate. However, a positive result still requires follow-up testing to confirm the diagnosis.
Current Status and Future of MCED Tests
MCED tests are not yet widely available for routine clinical use but are being evaluated in large-scale clinical trials. The PATHFINDER study, for example, is assessing the clinical utility of these tests in primary care settings. Researchers hope that MCED tests will eventually become a standard part of cancer screening, especially for high-risk individuals.
FAQs About Blood Tests for Cancer
Can a blood test alone diagnose cancer?
No, a blood test alone cannot diagnose all types of cancer. It is often used in combination with other tests.
What cancers can be detected by blood tests?
Blood tests are most effective for blood cancers like leukemia and lymphoma. Some solid tumors can also be detected, but imaging and biopsies are usually needed.
What is the Galleri test?
The Galleri test is a multi-cancer early detection test that can identify more than 50 types of cancer from a single blood draw by analyzing cell-free DNA and methylation patterns.
How accurate are MCED tests?
MCED tests like Galleri have shown high accuracy, with a false-positive rate of about 0.5%. However, a positive result requires further testing to confirm the diagnosis.
Are MCED tests available for everyone?
MCED tests are not yet widely available for routine clinical use but are being evaluated in clinical trials. They may become more accessible in the future.
References
References
- Multi-Center Clinical Trial Involving Cleveland Clinic Finds New Blood Test Accurately Detects Over 50 Types of Cancer — Cleveland Clinic Newsroom. 2020-05-18. https://newsroom.clevelandclinic.org/2020/05/18/multi-center-clinical-trial-involving-cleveland-clinic-finds-new-blood-test-accurately-detects-over-50-types-of-cancer
- A Single Blood Test Can Detect More Than 50 Types of Cancer — Consult QD, Cleveland Clinic. https://consultqd.clevelandclinic.org/a-single-blood-test-can-detect-more-than-50-types-of-cancer
- The Galleri Test for Cancer Screening — Health Cleveland Clinic. https://health.clevelandclinic.org/the-galleri-test
Similar Articles
Read full bio of Sneha Tete
