Tumor Markers The most important are tests for chemicals called tumor markers. These are produced by various types of tumors. Breast, lung and bowel tumors, for example, produce a protein called the carcinoembryonic antigen (CEA). Some inflammatory diseases may produce low levels of this chemical, but some tumors in these areas produce very high levels. If a very high CEA level is found, then a tumor is assumed to be present until proved otherwise. Similarly, prostate cancers and many cancers of the testicles and ovaries produce known chemicals.
Some very exciting research is now being done to find more and more accurate markers for different types of cancer. We can now envision the day in the not too-distant future when specific blood tests will identify most human cancers. But at the moment, the few tests we do have are invaluable. They not only help make the diagnosis but are especially useful for keeping track of the cancer after treatment. If the marker is elevated at the time of diagnosis, then successful treatment should result in the level falling or disappearing altogether. The reappearance of the marker often signals a relapse. If that happens, even if no other sign or symptom appears, there would be a search for a new tumor and consideration would be given to retreatment.
Other Blood Tests When a cancer is in the blood cells themselves, tests of the blood and the blood-forming organs may be all that's needed to make the diagnosis. Cancer of the white blood cells—leukemia—can often be diagnosed by looking at a sample of blood taken from the finger or arm. The diagnosis can be confirmed by examining cells from the bone marrow , where these cells are made. Bone marrow analysis will also diagnose multiple myeloma , which is basically a malignancy of plasma cells in the marrow.
