Blood tests can screen for cancer in healthy people and can help diagnose cancer in those with disease symptoms. Blood tests can also be used to monitor a person's response to cancer treatments and detect tumor recurrence. Doctors look for the presence of cancer cells in the blood or tumor markers, which are substances made by a cancerous tumor.
Blood Tests to Screen for Cancer
Blood tests can be used to screen healthy people for cancer. Prostate-specific antigen is sometimes used for prostate cancer screening, but PSA levels can be high for reasons other than cancer. The American Society of Clinical Oncology recommends that PSA screening should only be done in men expected to live longer than 10 years after discussing risks and benefits with their doctors.
Alpha-fetoprotein is a marker used to screen for liver cancer in people with a high risk of developing the disease. Organizations differ on their recommendations for its use because of the test's limited sensitivity. The National Academy of Clinical Biochemistry USA recommends AFP testing combined with ultrasound imaging. The American Association for the Study of Liver Disease recommends the use of the AFP test only when an ultrasound is not available.
Blood Tests to Diagnose Cancer
Blood tests combined with other diagnostic tools are used to diagnose cancer in people with disease symptoms. CA-125 is a tumor marker that can help determine if a woman has ovarian cancer that may spread to other sites. The U.S. Food and Drug Administration has approved CA-125 testing in combination with another marker, called HE4, to estimate the risk of ovarian cancer in women with an ovarian growth. Additional testing is needed to confirm the diagnosis.
AFP can be used to diagnose cancer in people who have a liver tumor larger than 2 cm. By testing for AFP, a liver biopsy can be avoided. AFP testing is not recommended for diagnosing liver masses smaller than 2 cm.
Complete blood counts and blood smears are used to diagnose blood cancers, such as leukemia. These tests detect differences in the number, size and maturity of white and red blood cells. People with leukemia typically have an elevated number of white blood cells. When examined under the microscope, the cancerous cells have characteristics that distinguish them from normal white blood cells.
Blood Tests for Cancer Recurrence
Blood tests can be used to monitor for recurrence of cancer after completion of therapy. After surgery for colorectal cancer, people are regularly screened for carcinoembryonic antigen. High CEA levels could mean the cancer has returned.
CA-125 can be measured following ovarian cancer treatment. High levels may mean the cancer has returned. Some studies suggest that CA-125 follow-up testing is not beneficial and may lead to decreased quality of life. The National Comprehensive Cancer Network states that regular testing for CA-125 should be optional and discussed with a doctor.
Men with testicular cancer who had treatment are regularly screened for AFP and human chorionic gonadotrophin. If the hCG levels are high, the cancer has likely returned.
Tumor marker testing remains a focus of cancer research, as scientists and doctors search for better methods for early detection of cancer. You should always discuss the interpretation of tumor marker tests with your doctor, because many factors can affect various tumor marker levels.