A tumor marker is any substance found in the body that may indicate the presence of cancer or other conditions. These substances are typically measured in blood, urine, or tissue samples to provide information about a cancer, such as its aggressiveness or its response to treatment. An elevated marker level does not automatically confirm a cancer diagnosis.
Understanding Tumor Markers
Tumor markers are biological molecules, such as proteins, hormones, or enzymes, produced either by the cancer cells themselves or by the body in response to tumor growth. These substances are detected and measured in various bodily fluids, most commonly in the bloodstream. Markers can also be identified through genomic markers, which include tumor gene mutations found in the tissue or shed into the blood.
Non-cancerous conditions, such as inflammation, benign tumors, or certain lifestyle factors like smoking, can cause tumor marker levels to rise. Not every person with a specific type of cancer will have a high level of the associated marker. Therefore, clinicians must combine tumor marker results with other tests, like imaging or biopsies, to reach a diagnosis.
How Markers Are Used in Patient Care
The primary application of tumor markers is managing cancer once a diagnosis has been established. They are used to monitor how well a patient is responding to specific treatments, such as chemotherapy or radiation. A consistent decrease in the marker level suggests that the therapy is working to reduce the tumor burden.
Markers are also frequently used for surveillance after a patient has completed initial treatment. Regular testing helps check for possible cancer recurrence, as a steadily rising level can be an early sign that the disease has returned. High tumor marker levels can also help clinicians determine the stage of the cancer or estimate the likely course of the disease. Markers are rarely used for screening the general population because their lack of specificity can lead to false-positive results and unnecessary follow-up procedures.
Three Important Tumor Markers
Prostate-Specific Antigen (PSA)
Prostate-Specific Antigen (PSA) is a protein produced by both healthy and cancerous cells in the prostate gland. The PSA test measures the amount of this protein in the blood and is specifically associated with prostate cancer. Its use for general screening is controversial due to low specificity, as benign prostatic hyperplasia (BPH) and inflammation can also cause elevation.
PSA is widely accepted as a tool for monitoring men already diagnosed with prostate cancer. Serial measurements monitor disease progression and assess treatment effectiveness. A rapid increase in PSA levels after surgery or radiation therapy is often the first indicator of cancer recurrence, sometimes appearing months before physical symptoms.
Carcinoembryonic Antigen (CEA)
Carcinoembryonic Antigen (CEA) is a glycoprotein primarily associated with cancers of the gastrointestinal tract, especially colorectal cancer. It can also be elevated in lung, breast, and ovarian cancers. CEA is a cell-surface protein normally produced during fetal development, with very low levels present in healthy adults.
For patients with colorectal cancer, CEA testing is a standard method for monitoring treatment response and detecting recurrence. A decrease in the level during therapy suggests a positive response, while an increase after treatment often signals that the cancer has returned. Non-cancerous conditions like inflammatory bowel disease, liver disease, and smoking can also cause an increase in CEA levels.
Cancer Antigen 125 (CA-125)
Cancer Antigen 125 (CA-125) is a glycoprotein used in the management of ovarian, fallopian tube, and primary peritoneal cancers. The protein is found on the surface of these cancer cells and is released into the bloodstream, allowing its concentration to be measured.
CA-125 is most often used to monitor the effectiveness of ovarian cancer treatment, with declining levels suggesting the tumor is shrinking. It is also utilized to check for disease recurrence after treatment has concluded. CA-125 levels can be elevated by non-cancerous conditions, including endometriosis, uterine fibroids, and menstruation.