Doctor, do I have cancer? Can you run all of the tests to check?"These are questions I hear regularly. The answers are more complicated than you would think. Science has indeed come a long way in discovering "markers" to follow the progress of cancer treatment in the body, but how much do we know about early detection? What can we do as part of a routine exam to discover hidden cancers? Tumor markers are substances that can be found in abnormal amounts in the blood, urine, or tissues of some patients with cancer. Different markers are found with different types of cancer, but scientists have not found markers for every type of cancer. Tumor markers are produced by tumor cells, or by other cells of the body in response to the tumor. However, tumor marker levels are not altered in all people with cancer, especially if the cancer is in early stages. Markers may be used to help diagnose cancer, predict a patient's response to a particular treatment, or determine if the cancer has returned. To date, researchers have identified more than a dozen substances that appear to be abnormal when some type of cancer is present. At the present time, the use of tumor markers in clinical medicine is limited. Although an abnormal tumor marker level may suggest cancer, this alone is usually not enough to make the cancer diagnosis. Therefore, this information is usually combined with a patient's history, other blood tests, x-rays, and biopsies. After the diagnosis, tumor markers may be measured before a cancer treatment to help doctors plan the appropriate therapy. In some cancers, the level of tumor marker may reflect the stage of the disease. During treatment, decreasing levels of tumor marker can reflect a good response to treatment. But, in terms of screening for the presence of cancer, tumor makers thus far have limited usefulness. A screening test is a way of detecting cancer early, before there are any symptoms. For a screening test to be helpful, it should have high sensitivity and high specificity. Sensitivity refers to the test's ability to identify people who have the disease. Specificity refers to the test's ability to identify people who do not have the disease. Unfortunately, tumor markers are neither sensitive nor specific enough to be used for cancer screening. For example, prostate-specific antigen (PSA) levels are often used to screen men for prostate cancer, but this is controversial. It is not yet known whether early detection using PSA screening actually saves lives. Elevated levels of PSA can be caused by prostate cancer or by benign conditions, and most men with elevated levels turn out to not have prostate cancer. Further, it is not known if the benefits of PSA screening outweigh the risks of follow-up diagnostic tests and cancer treatments. Another tumor marker, the CA 125, is sometimes used to screen women who have an increased risk for ovarian cancer. Scientists are currently studying whether measurement of CA-125, along with other tests and exams, is useful to find ovarian cancer before symptoms appear. Thus far, CA-125 is found to be neither sensitive nor specific enough to justify screening all women. At this point, CA-125 is used to monitor responses to treatment of ovarian cancer and check for recurrence. For now, we doctors spend most of our cancer-fighting efforts working with our patients to eliminate underlying risks that are known to cause future cancers, such as cigarettes, excessive alcohol, too much exposure to the sun, obesity, diet, and environmental exposures. Actual cancer detection more typically happens as a result of listening to a patient's complaints, performing a physical exam, and then performing tests to confirm any suspicions. But, stay tuned. As science advances, health professionals constantly have more tools at their disposal. In the meantime, prevention is key. Good health to you all! Dr. Alan Frischer is former chief of staff and former chief of medicine at Downey Regional Medical Center. Write to him in care of this newspaper at 8301 E. Florence Ave., Suite 100, Downey, CA 90240.
********** Published: November 11, 2010 - Volume 9 - Issue 30