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Benefits and Limitations of Tumor Markers

Several types of tests can help oncologists diagnose cancer and determine a prognosis (determining the outcome). These tests are an important part of follow-up care after cancer treatment. Among the tests are tumor markers, also known as cancer biomarkers.

Overview

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Tumor markers are substances (usually proteins) that are abnormally expressed in the body when cancer is present. These substances are either produced by cancer cells themselves or by other cells in response to cancer and can be found in the blood, urine or tumor tissue.

Although tumor markers can be valuable, especially for some types of cancer, they also have limitations. The primary limitation is that many tumor markers are not cancer specific; that is, they may be elevated in conditions other than cancer. Consequently, other tests may be needed to confirm a diagnosis of cancer. In addition, some tumor markers are not elevated in all patients with a particular cancer, which means those markers cannot reliably identify all patients who have that cancer. Lastly, tumor markers are not available for all types of cancers.

How tumor markers are used varies according to the type of cancer (Table 1). Tumor markers as a screening tool would provide an important advantage, as they would aid in early detection and early treatment. However, only one tumor marker — prostate-specific antigen (PSA) — has been found to be useful for screening, and the benefit of even this marker as a screening tool is debated. The primary use of tumor markers is in the follow-up setting, where an increasing level of a tumor marker during or after treatment may indicate a poor response to treatment or the recurrence or progression of cancer.

Only a few tumor markers are recommended for routine use, and many others continue to be studied to determine their value (Table 2). Each individual with cancer should talk to his or her oncologist about which tumor markers may be appropriate.

How Tumor Markers Are Used

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Screening	Most tumor markers are not useful for screening; only 1 tumor marker (prostate-specific antigen) is used for screening
Diagnostic Aid	Tumor markers can help identify the type of cancer when considered along with other clinical factors, such as symptoms and findings on imaging studies
Determine Prognosis	Some tumor markers are factors considered when determining prognosis, or a prediction of the outcome
Guide Treatment	Some tumor markers can provide information about what types of treatment are more likely to produce a response
Monitor Response to Treatment	Tumor markers can monitor the effectiveness of treatment, especially for advanced cancers
Detect Recurrence or Progression	One of the primary uses of tumor markers; if the level of a tumor marker is elevated before treatment, is low after treatment, and then begins to increase after treatment, it is likely that cancer is recurring or progressing

Tumor Markers Based On Cancer Type

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Tumor Marker	Type of Sample	Use	Comments on Use	Recommendations**
Bladder Cancer
BTA (bladder tumor-associated antigen)	Urine	Aid diagnosis Detect recurrence/progression	Cystoscopy remains the standard for diagnosis and follow up	Insufficient evidence to recommend its use
Breast Cancer
CA (cancer antigen) 15-3 or CA 27.29	Blood	Monitor response	Should not be used alone to monitor response	ASCO: May be used to monitor response to treatment in conjunction with diagnostic imaging, history and physical examination
CEA (carcinoem- bryonic antigen)	Blood	Monitor response	Should not be used alone to monitor response	ASCO: May be used to monitor response to treatment in conjunction with diagnostic imaging, history and physical examination
ER/PR (estrogen receptor)/(progesterone receptor)	Tissue	Guide Treatment	Identifies tumors that are most likely to respond to hormone therapy (tamoxifen)	ASCO and NCCN: Determine ER/PR status at diagnosis for all primary invasive breast cancers ^a
Gene expression analysis	Tissue	Determine prognosis Guide Treatment	Genetic profile of tumor predicts risk of recurrence in distinct population of women (see next column) Low risk score indicates that woman can be treated safely with tamoxifen alone (without chemotherapy)	ASCO and NCCN: Use gene expression analysis (Onco type DX) ^bfor newly diagnosed early-stage disease that is ER/PR-positive, with no evidence of disease in the lymph nodes
HER2/neu antigen	Tissue	Guide Treatment	Identifies tumors that are most likely to respond to treatment with trastuzumab (Herceptin) and to some specific chemotherapy drugs	ASCO and NCCN: Determine HER2/neu status at diagnosis for all primary invasive breast cancers
uPA (urokinase-type plasminogen activator), PAI-1	Tissue	Determine prognosis Guide Treatment	Low levels indicate low risk of recurrence in receptor-positive breast cancer Low level (low risk) indicates that woman will have minimal benefit from chemotherapy	ASCO: May be used to determine prognosis in newly diagnosed, node-negative disease
Colorectal Cancer
CEA	Blood	Determine prognosis Monitor response Detect recurrence/progression	High level before treatment may indicate cancer is metastatic	ASCO: Marker of choice for monitoring metastatic colorectal cancer during treatment with chemotherapy; use during follow up of nonmetastatic disease to detect recurrence or metastasis NCCN: Determine level during initial workup and throughout follow up at specified intervals
Liver Cancer
AFP (alpha- fetoprotein)	Blood	Aid diagnosis Detect recurrence/progression	Levels can be increased in other noncancerous conditions, but very high levels can indicate liver cancer	NCCN: Determine level during initial workup and throughout follow up (at specified intervals) if the level was initially elevated
Melanoma
LDH (lactate dehydrogenase)	Blood	Determine prognosis	High level is predictor of poor prognosis; LDH level is factor used in determining the stage of disease	NCCN: Determine level during initial workup and throughout follow up of stage IV (metastatic) melanoma at specified intervals
S-100	Blood	Detect progression	Elevated in most individuals with metastatic melanoma	Insufficient evidence to recommend its use
Multiple Myeloma
Beta-2-microglobulin	Blood	Determine prognosis Monitor prognosis	Standard measure of tumor burden; higher levels indicate poorer prognosis	NCCN: Determine level during initial workup and throughout follow up at specified intervals
Ovarian Cancer
CA-125	Blood	Aid diagnosis Detect recurrence/progression	Standard marker for follow up	NCCN: Determine level during initial workup if symptoms suggest ovarian cancer and determine level throughout follow up (at specified intervals) if level was initially elevated
Pancreatic Cancer
CA 19-9	Blood	Determine prognosis Monitor response	High level is associated with poor prognosis Decreased level after surgery or chemotherapy indicates better survival	ASCO: Use to monitor response during active treatment for locally advanced metastatic disease; if level increases after treatment, use imaging studies and/or biopsy to confirm recurrence NCCN: Determine level during initial workup and throughout follow up
Prostate Cancer
PSA	Blood	Screening Detect recurrence/progression	PSA is elevated in benign prostate conditions, making interpretation of results complex: about 3 in 4 men who have an elevated PSA do not have prostate cancer; in contrast, some men with prostate cancer do not have an elevated PSA	ACS, AUA and NCCN: Determine PSA level (with digital rectal examination) annually beginning at age 50 USPSTF and ACP: Annual screening with PSA not recommended as clear benefit has not been demonstrated
Testicular Cancer
AFP	Blood	Aid diagnosis	Levels are factors used in determining stage of disease	NCCN: Determine levels during initial workup and throughout follow up
hCG (human chorionic gonadotropin)	Blood/urine	Determine prognosis
LDH	Blood	Guide treatment	More aggressive treatment is recommended if elevated levels persist

*Note: There are many ongoing clinical trials of tumor markers, and the information in this table may change as a result of their findings. Patients are advised to consult with their physicians for up-to-date information.

a) NCCN recommends determining the ER/PR status for ductal carcinoma in situ (DCIS), but ASCO guidelines state that there is insufficient evidence to recommend routine determination of ER/PR status to guide treatment decisions for women with DCIS.

b) For more information on Onco type DX and other gene expression analysis tests, see article, page 42.

**ASCO = American Society of Clinical Oncology; NCCN = National Comprehensive Cancer Network; ACS = American Cancer Society; AUA = American Urological Association; USPSTF = U.S. Preventive Services Task Force; ACP = AmericanCollegeof Physicians.