Tumor markers are substances found in higher than normal amounts in the blood, urine, or body tissues of some people with cancer. They are produced either by the tumor itself or by the body in response to cancer growth. An elevated tumor marker level can indicate the presence of cancer but does not diagnose a specific type of cancer.
What are tumor markers?
Tumor markers are proteins or other substances produced by cancer cells or by the body in response to cancer growth. Here are some key points about tumor markers:
- Higher than normal levels can indicate the presence of cancer but do not diagnose a specific type of cancer.
- Levels can be elevated by noncancerous conditions such as infection, inflammation, and benign tumors.
- Most tumor markers are not specific enough to use alone for cancer screening or diagnosis.
- Monitoring levels over time can be useful to determine how well treatment is working or if cancer has returned.
- Some common tumor markers used to monitor certain cancers include PSA, CA-125, AFP, CEA, CA 15-3, CA 19-9.
So in summary, an elevated tumor marker level indicates there may be cancer present but does not confirm cancer by itself. Further testing is needed to determine the cause of the elevated level.
Common causes of elevated tumor marker levels
There are several potential causes of an elevated tumor marker level other than cancer. Some common reasons include:
- Infection or inflammation – Many conditions that cause inflammation or irritation can mildly elevate tumor markers. This includes infections, autoimmune disorders, and non-cancerous growths.
- Liver disease – Liver damage or dysfunction can raise AFP and CEA levels.
- Kidney disease – Reduced kidney function can lead to higher levels of substances normally filtered out by the kidneys.
- Smoking – Tobacco use increases tumor marker levels, especially CEA levels.
- Age – Levels of some markers can gradually rise as a person gets older.
- Medications – Certain prescription and over-the-counter medications are known to elevate specific tumor markers.
- Pregnancy – Some tumor markers like AFP and hCG are elevated during pregnancy.
- Benign tumors – Noncancerous growths can mildly raise tumor marker levels in some cases.
- Strenuous exercise – Intense physical exertion may temporarily elevate certain markers.
So while an elevated tumor marker could indicate cancer, there are many other potential causes that should be explored especially if there are no other signs of cancer present.
Tumor markers used to detect and monitor cancers
While tumor markers have limited use for cancer screening in healthy people, they are often used to detect recurrences and monitor cancers that are known to elevate specific markers. Some examples include:
- PSA for prostate cancer – PSA is often used to screen for prostate cancer with a digital rectal exam. It is also measured periodically after treatment.
- CA-125 for ovarian cancer – Levels of CA-125 are measured before surgery and to monitor response to ovarian cancer treatment.
- AFP for liver cancer – AFP is sometimes measured to help detect and monitor hepatocellular carcinoma.
- CEA for colorectal cancer – CEA levels help determine if colorectal cancer treatment is working.
- CA 15-3 for breast cancer – Elevated CA 15-3 may indicate recurrence in women previously treated for breast cancer.
- hCG for gestational trophoblastic disease – hCG levels are used to diagnose and monitor treatment for gestational trophoblastic tumors.
Doctors must always consider the whole clinical picture when interpreting tumor marker results, not just the levels alone. But abnormally high levels can prompt further testing like imaging scans to search for malignancy.
How significantly must a tumor marker be elevated to be concerning?
How concerning a mildly vs significantly elevated tumor marker level is depends on the specific marker, the degree of elevation, and the clinical scenario. Some general guidelines on significant tumor marker elevations include:
- PSA levels above 4 ng/mL are often considered elevated and warrant further testing.
- AFP levels above 500 ng/mL are highly suspicious for liver cancer.
- CA-125 levels over 35 U/mL are typically abnormal in women without ovarian cancer.
- CEA levels above 5 ng/mL frequently indicate colorectal cancer recurrence.
- CA 15-3 levels over 25 U/mL may signify metastatic breast cancer.
- hCG levels higher than expected in pregnancy warrant evaluation for gestational trophoblastic disease.
However, the trend of the tumor marker over time is often more telling than a single abnormal value. A rapidly increasing level is more concerning than a slight bump just over the normal threshold. Doctors also consider any symptoms and results of other testing when interpreting tumor marker levels.
How are tumor marker levels monitored during cancer treatment?
Tumor marker levels are often monitored periodically during cancer treatment to gauge the effectiveness of therapies. In general:
- Decreasing levels indicate treatment is working to destroy cancer cells.
- Increasing levels after treatment suggest cancer is progressing or recurring.
- Stable levels that remain elevated imply residual cancer is still present.
- Tumor marker normalization is a positive prognosis for complete cancer elimination.
Frequent tumor marker testing allows doctors to quickly change treatment plans if levels rise. This helps prevent cancers from advancing and improves outcomes. Some general guidelines on monitoring frequency include:
- Every 1-3 months for cancers like colon, ovarian, liver, stomach, pancreas.
- Every 3-6 months for cancers like prostate, kidney, bladder.
- Every month at first, spreading out over time for cancers like germ cell tumors.
Doctors may adjust the schedule based on the aggressiveness of cancer and how treatment is progressing. More frequent monitoring occurs after active treatment ends when recurrence risk is highest.
Can tumor marker levels fluctuate up and down?
Yes, it is possible for tumor marker levels to fluctuate up and down over time. Reasons this may occur include:
- Lab errors in the testing procedure, requiring repeat testing.
- A temporary spike due to something like infection or inflammation.
- Variation after initial cancer treatment as remaining cells die off.
- Increase from rapid growth, decrease from effective treatment killing cancer cells.
- Levels going up and down as cancer waxes and wanes.
For these reasons, doctors usually look at trends in tumor marker levels rather than basing decisions on a single abnormal value. However, a rapid or substantial rise requires prompt evaluation to determine if cancer is progressing or has recurred.
Can tumor marker levels be normal even if cancer is present?
Yes, it is possible for tumor marker levels to be within the normal range even when active cancer is present. Reasons this can occur include:
- The tumor type does not elevate the particular marker tested.
- The tumor is small and not shedding enough marker substances yet.
- An individual cancer is not making much of that biomarker protein.
- Production is patchy, escaping into spaces not measured in blood or urine.
- Marker levels have not risen high enough to be abnormally elevated.
- The test cutoffs fail to detect raised levels in that person.
Normal tumor marker levels do not definitely rule out cancer, especially if symptoms are present. Further imaging or biopsy may be warranted for definitive diagnosis. But in the absence of other indications of malignancy, normal levels provide reassurance.
How are tumor marker levels used to detect cancer recurrence?
Monitoring tumor marker levels at regular intervals after cancer treatment is completed is a common way to try detecting potential disease recurrence early. This allows any rising levels to prompt further investigation and earlier intervention if cancer has returned. Some key points about using tumor markers to monitor for recurrence include:
- Frequent testing every 3-6 months for the first 2-5 years when recurrence risk is highest.
- Checking levels of the marker associated with the original cancer type.
- Looking for upward trend vs stable or decreasing marker levels over time.
- Correlating results with any new or worsening symptoms reported.
- Following up abnormal levels with imaging scans to identify areas of concern.
- Changes in therapy if recurrent cancer is confirmed.
This approach can detect relapse months earlier than waiting for symptoms to appear. Early detection of rising tumor marker levels allows prompt treatment before cancer advances too far. Monitoring even after 5 years is advised for high-risk cancers.
How reliable are tumor markers for detecting cancer?
Most tumor markers lack the reliability to definitively diagnose cancer based on levels alone. This is because levels can be elevated by many noncancerous conditions. However, their accuracy and reliability for detecting cancer increases when:
- Levels are significantly higher than the normal cutoff for that marker.
- Levels keep rising on repeat testing over time rather than fluctuating.
- The patient has suspicious symptoms correlated with a particular cancer.
- Marker elevations correspond with abnormal imaging study findings.
- Levels decline after cancer treatment and rise again later.
So while nonspecific when considered alone, tumor markers form a useful part of the total information doctors utilize to diagnose and manage cancers. Skilled interpretation based on the full clinical picture is important for optimal accuracy.
Conclusion
In summary, tumor markers are substances that can be elevated by cancer growth but also by various benign conditions. The levels alone do not diagnose cancer but are often used to detect recurrence and monitor treatment response when cancer is already present. Doctors must interpret marker results in the full clinical context for optimal reliability. Awareness of the factors that can cause tumor marker elevations allows appropriate evaluation and action when levels rise.