Tumor markers are substances, often proteins, that are produced by cancer cells themselves or sometimes by the body in response to uncontrolled cell growth. Because some of these substances can be detected in body samples such as blood, urine, and tissues, these markers can be used, along with other tests and procedures, to help detect and diagnose certain types of cancer, predict and monitoring a person’s response to certain treatments and detect recurrences.
Recently, the idea of what constitutes a tumor marker has expanded. New types of tests have been developed that require changes in genetic material (DNA, RNA), rather than proteins, inpatient samples. Genetic changes have been found to be associated with certain cancers and can be used as tumor markers to help determine the prognosis, guide targeted treatment, and/or detect cancers early. Moreover, advances in technology have led to tests that can evaluate several genetic markers or marker panels at the same time, providing extended information about the characteristics of a tumor. Examples of these are included, along with the most traditional tumor indicators, in the table within this article.
While many tumor markers are available and have been found to be clinically useful, others are available but not frequently ordered because they have been found to be less sensitive and/or specific. Still, others are currently only used in research settings and continue to be evaluated in clinical trials. With ongoing research, and as the field continues to evolve, it is likely that more tumor markers with greater effectiveness will come to market in the coming years, eventually replacing the less useful ones.
While tumor marker tests can provide very useful information, they have limitations:
- Many tumor markers can also be raised in people with conditions or diseases other than cancer.
- Some tumor markers are specific to a particular type of cancer, while others are seen in several different types of cancer.
- Not every person with a particular type of cancer will have an elevated level of the respective tumor marker.
- Not every cancer has a tumor marker that has been identified as associated with it.
- Consequently, tumor markers alone are not diagnostic of cancer; for some types of cancer, they provide additional information that may be considered about a patient’s medical history and physical examination, as well as other laboratory and/or imaging tests.
How are tumor markers used?
Tumor markers can be used for a variety of purposes. However, they are not usually used alone. Depending on the type of cancer, they may be used in conjunction with a tissue biopsy or bone marrow or blood-staining examination, for example, and/or with other tumor markers. They are not final, but provide additional information that can be used to help:
Because most tumor markers are not sufficiently sensitive or specific, these tests are not suitable for controlling the general population; however, some can be used to control people who are at high risk because they have a family history or specific risk factors for particular cancer.
Assist in diagnosis. In a person who has symptoms, tumor markers can be used to help detect the presence of cancer and to help distinguish it from other conditions with similar symptoms.
Stage. If a person has cancer, elevations of tumor markers can be used to help determine if cancer has spread (metastasized) to other tissues and organs and to what extent.
Determine the prognosis. Some tumor markers can be used to help determine how aggressive a cancer is likely to be.
Guiding choice of treatment. Some tumor markers provide information on which treatments can be effective against a person’s cancer. This is a growing research area. For more information, see the article Genetic Tests for Targeted Cancer Therapy.
Monitor treatment success and detect recurrence. Tumor markers can be used to monitor the effectiveness of treatment, especially in advanced cancers. If the marker level drops, the treatment is working; if it remains elevated, adjustments are needed. (Information should be used with caution, however, as other conditions can sometimes cause tumor markers to rise or fall.) One of the most important uses for tumor markers, along with guideline treatment, is to monitor the recurrence of cancer. If a tumor marker is raised before treatment, low after treatment, and then begins to grow over time, then it is likely that the cancer is coming back. (If left untreated after surgery, chances are not all of cancer will be removed.
- BR-MR (CA 15-3)
- GI-MA (CA 19-9)
- OM -MA (CA 125)
- CA 72-4
- PAP (a dry prostatic phosphatase)
- PSA 3rd Generation
- Free PSA
- HE 4
- Chromogranin A
- CEA quantum
- Figure 21-1
- Roma INDEX.