What are tumor markers?
They are proteins that are shed by cancer cells in greater numbers than normal cells. These would be desirable as screening tests because blood tests can measure their circulating levels.
None of them have proven their benefit in saving lives due to early diagnosis. Their value lies in measuring response to treatment in advanced cancers, once the cancer has been diagnosed and treated. If the numbers are elevated at the time of diagnosis, then watching the number go down is a reassurance that the cancer treatment is working.
PSA has been in the news lately, because of the Prostate Cancer screening recommendations. The PSA has been followed diligently for early diagnosis of prostate cancer, leading to innumerable biopsies. These have led to early, and possibly unnecessary treatment of prostate cancer.
CA 125 has been touted as a marker for ovarian cancer. It is a good test to follow the course of the cancer once it has been diagnosed, but not as a screening test. It is not specific to only ovarian cancer, and is increased in other benign situations.
CEA is another blood test that is followed in colon cancer and lung cancer. It is artificially increased in smokers.
CA 19-9 is a protein associated with Pancreatic Cancer.
CA 15-3 and CA 27.29 are associated with Breast Cancer.
There are fluctuations in the levels of these tests; we’re looking for trends, or large shifts.
Other blood tests measure activity of some cancers, e.g.
Lymphomas : LDH, ESR
Multiple myelomas: Protein light chains, and Immunoglobulin levels, etc. These are otherwise normal proteins present in abnormal numbers and ratios, because of overproduction by the myeloma cell.