By Cat Troiano
More than 1.5 million Americans are estimated to be diagnosed with new cancer cases this year, according to the American Cancer Society projections. Cancer remains one of the leading causes of mortality in the United States, with more than 600,000 deaths predicted for 2018. These numbers are disconcerting to everyone, but encouraging statistics reveal that the overall cancer mortality rate for some types of cancer dropped by 25 percent from 1990 to 2014. This is due in part to research advancements that have led to more effective treatment protocols as well as improved cancer screening methods. Some types of cancer can even be detected in a sample of blood, thanks to their tell-tale tumor markers.
What Are Tumor Markers?
In addition to red blood cells, white blood cells and platelets, blood contains other substances, including proteins, antigens, enzymes and other biochemical matter. Some cancer patients can have abnormally high levels of specific substances in their blood. As their illness advances, the levels increase, but if their cancer treatment is effective in combatting their illness, then the levels decrease. These demonstrated fluctuations have led to the identification of such biochemicals as tumor markers, which may increase as a result either from the body’s immune response to the illness or from the tumor’s cells as they produce more of the tumor marker. Some tumor markers can also be found in urine, bone marrow and tissue samples. The majority of tumor markers are proteins, but progress in genetic research has paved the way for the development of tests that evaluate changes in the genetic material of cancer patients.
What Are Tumor Marker Tests Used For?
Once patients have been diagnosed with certain types of cancer, tumor marker tests can provide helpful information for physicians in their quests to provide successful treatment. Some ways in which tumor marker test results are used include:
- Monitor treatment progress – when tumor marker tests are periodically performed throughout the cancer treatment duration, the results can reveal if the treatment protocol is working. A decrease in the tumor marker level indicates success. Conversely, an increase in the tumor marker level indicates that the disease is advancing.
- Detect cancer recurrence – when tumor marker tests are periodically performed once a patient has entered remission, the results can reveal if the cancer recurs.
- Stage cancer by detecting metastasis – based on how high the elevated tumor marker level is, physicians can get an idea of how advanced the patient’s cancer is and whether or not the disease has metastasized, or spread, to other areas of the body.
- Guide treatment option choice – some tumor markers can help oncologists to determine which treatment protocols will be the most successful for their patients.
- Predict prognosis – when compared with similar tumor marker test results of other patients, the prognosis for a new patient’s cancer treatment outcome can be predicted based on that of those other previous patients.
All of the aforementioned can be beneficial in guiding and tracking cancer treatment, but what about cancer screening and diagnosis?
Can Tumor Marker Tests Diagnose Cancer?
According to the National Cancer Institute, there are more than 100 different types of cancer. There are not tumor marker tests for all of them because researchers have not yet identified specific tumor markers for each and every type of cancer. Another problem is that while some tumor markers are specific to one particular cancer, others can become elevated by any one of several types of cancer. Furthermore, some tumor markers can become elevated for reasons other than cancer. Finally, not every individual who has cancer will have an elevation in the specific tumor marker’s level, especially if the cancer is in its early stage. Despite these limitations, there are a few tumor marker tests that can contribute to the screening and diagnostic process. The following tests are performed as a step toward diagnosis, and they are further used to monitor cancer treatment and to screen for recurrence.
Prostate specific antigen (PSA)
- This test screens for prostate cancer.
- The normal reference range for PSA is less than 4 ng/ml.
- PSA is an example of a tumor marker that is specific to prostate cancer and not to other types of cancer. The PSA test is recommended as a routine screening for all male patients who are 50 years of age or older and have a remaining life expectancy of ten years or longer.
- Some benign conditions, such as prostate enlargement or prostate inflammation, can cause an elevation in the PSA level.
- This test detects the presence of medullary thyroid cancer.
- The normal reference range for calcitonin is less than 8.5 pg/mL in men and less than 5.0 pg/mL in women.
- Chronic proton-pump inhibitor treatment as well as chronic renal failure can cause an increase in the calcitonin level.
- This test can detect the presence of liver cancer. Elevations can also be indicative of other cancers, including germ cell ovarian cancer and testicular cancer.
- The normal reference range for AFP is 0 to 15 IU/ml.
- An elevation in AFP can result from some noncancerous conditions as well, including inflammatory bowel disease, cirrhosis and hepatitis.
Cancer antigen 125 (CA 125)
- This test detects the presence of epithelial ovarian cancer, which is the most commonly diagnosed type of ovarian cancer.
- The normal reference range for CA 125 is 0 to 35 U/ml.
- An elevation in CA 125 can also occur in patients with breast cancer and colorectal cancer. Some noncancerous conditions that can cause an elevation in CA 125 include inflammatory bowel disease, pancreatitis, peritonitis, endometriosis and ovarian cysts.
Human chorionic gonadotropin (hCG)
- This test is used to detect the presence of testicular cancer as well as germ cell ovarian cancer and choriocarcinoma.
- The normal reference range for hCG is less than 2.5 U/ml in men and less than 5.0 U/ml in non-pregnant women.
- hCG levels can rise in women who are pregnant as well as in patients with inflammatory bowel disease and duodenal ulcers.
Chromogranin A (CgA)
- This test can detect the presence of neuroendocrine and carcinoid tumors.
- The normal reference range for CgA is less than 39 ng/l.
- Chronic use of proton pump inhibitor drugs can also increase the level of CgA.
Neuron specific enolase (NSE)
- Although it is not used to diagnose lung cancer, this test helps to determine if a lung cancer case is small cell lung cancer, as opposed to non-small cell lung cancer. This test can also detect the presence of neuroblastoma.
- The normal reference range for NSE is less than 9 ug/L.
- NSA can also become elevated in patients with COPD and chronic bronchitis. Other causes of a high NSE level include stroke, seizure activity, end stage renal failure, liver failure and hemolytic anemia.
Even these few tests that do play a role in cancer screening should be used as just one piece of the diagnostic puzzle to be put together with other pieces, such as patient medical history, patient symptoms, diagnostic imaging tests and tissue biopsies, to achieve a definitive diagnosis.
Research is constantly underway to develop more tests with greater sensitivity to hone in on specific tumor markers. A new test that is currently under development has shown promise in its ability to detect any of eight different common cancers from one blood sample. In the meantime, there are already many more tumor marker tests available that are valuable tools in cancer treatment planning, implementation and monitoring. These benefits alone can make the difference needed to extend the life expectancies of patients who are diagnosed with cancer.