tumor markers Flashcards
Cancer
uncontrolled growth of cells that often forms a solid mass or tumor that may spread to
other areas of the body.
stages 1- 4
tumor markers
•Substances found in abnormally high concentrations in body fluids or tissues from cancer patients.
- can be produced by a variety of different tumors
- Few are organ-specific or specific for one type of malignancy
- Can be produced directly by the tumor or as an effect of the tumor on healthy tissue.
- Bence Jones protein in urine of multiple myeloma patients was first tumor marker identified (1847)
Characteristics of “Ideal” Tumor Markers
- Detectable in a given malignancy and absent in healthy populations ( sensitivity & specificity )
- Readily detectable in body fluids
- Present at concentrations proportional to tumor burden
- Conveniently measured by a readily available, simple, reproducible, and inexpensive procedure.
- Beneficial to clinical care with a measurable effect on patient outcome.
Applications of tumor markers
screening
- biopsy indication
diagnosis
- highlevels indicate disease
prognosis
- high levels indicate poor prognosis
Monitoring treament
- monitor efficacy ( see if levels are decreasing )
detection of reoccurrence
- increase associated with relapse
Applications of Tumor Markers - Screening
- High clinical sensitivity and specificity are required*****
- Example of population screening: Fecal occult blood testing for colorectal cancer
- No tumor markers identified to date can effectively screen asymptomatic patients.
- Most tumor markers currently used are also found in normal cells and benign conditions as well.
- Would lead to false positive results, undue alarm, unnecessary procedures
•Screening for susceptibility of certain cancers (breast, ovarian, colon) in those with a family history can be done using molecular diagnostics.
•Germ-line mutations are identified
- Example: BRCA1 and BRCA2 mutations for breast and ovarian cancers
Applications of Tumor Markers - Diagnosis
•High levels of tumor marker can be indicative of disease.
•High clinical sensitivity and specificity are again important.*****
- Cannot use a cutoff value for a tumor marker if healthy individuals can also have high values or if
individuals that have cancer can fall below the cutoff level.
- Most used in conjunction with symptoms, history, biopsies, ultrasounds, etc.
•Example of a diagnostic aid in high-risk groups:
•AFP (alpha fetal protein) testing as an addition to ultrasound for hepatocellular carcinoma (HCC)
- Used with patients who have cirrhosis who are at high risk of developing HCC
Applications of Tumor Markers - Prognosis
- High levels generally associated with poor prognosis.
* Concentrations increase with progression of tumor.
* Levels are highest when tumors metastasize.
•The presence or absence of a tumor marker may also be valuable and may be used to select chemotherapeutic treatment.
Applications of Tumor Markers - Monitoring
- One of most common and useful applications
- Monitoring therapy efficacy
- Detecting disease recurrence
•After treatment (surgical resection, radiation, drug therapy) tumor markers are often tested serially.
-Effective treatment will see a decrease or disappearance of the tumor marker
•Blood samples are easy to obtain to detect recurrence versus invasive procedures
-Levels of tumor markers in blood often rise before tumor can be detected by physical methods.
Preanalytical Requirements
Specimen Timing
•Timing not critical - no evidence of diurnal variation for most markers
•Pretreatment specimen should be taken - can help interpret subsequent results( get a baseline
level before treatment)
•Specimen should be taken prior to certain procedures that will transiently release tumor markers
into circulation
Ex. Colonoscopies, abdominal surgeries, prostate biopsies
Specimen Handling
•Serum or plasma appropriate for most measurements
•Gel tubes not suitable for some assays
Laboratory Considerations for Tumor Marker Analysis
- Size and variability of tumor marker concentration between different manufacturers
•Hard to compare patient results if different assays are used - Wide range of concentrations encountered
•Accurate measurement can be challenging
•Ex. hCG can range between 10 and 10,000,000 mIU/mL
Methods of Tumor Marker Detection
- Immunoassay
- High-Performance Liquid Chromatography
- Immunohistochemistry and Immunofluorescence
- Enzyme Assays
Methods of Tumor Marker Measurement - Immunoassay
•Most common method to measure tumor markers
- Can be automated, easy to use
•Considerations with immunoassays include: linearity, hook effect, and heterophile antibodies
Linearity ( immunoassays )
- If a sample exceeds the linear range, samples must be diluted to determine values within the
reportable linear range.- Risk of error if performing manual dilutions (have another tech review to reduce risk)
- Very high concentrations can lead to antigen excess (hook effect)
Hook Effect ( immuniassays )
- Analyte concentrations exceed the analytical range by a large amount.
- Tumor marker concentrations will be grossly underestimated.
- Typically only affects sandwich-type immunoassays.
•If tumor marker is expected to be higher than reported, dilute sample and repeat testing.
- Higher results will be obtained on the dilution if hook effect is present
Heterophile antibodies ( immunoassays )
- Circulating antibodies against human or animal immunoglobulin reagents( HAMA)
- Leads to false positive results (occasionally false negative)
•Perform dilutions to confirm heterophile antibodies are present
- Diluted samples will not give linear results if heterophile antibodies are present
Carryover ( immunoassays )
•Potential for carryover with high levels of tumor marker analytes
- Can lead to falsely elevated levels in patients
- Adequate wash steps can help prevent this
Methods of Tumor Marker Measurement - HPLC
•Used to detect catecholamine metabolites ( hormone made by adrenal glands) in plasma and urine.
- Analytes of interest are separated from plasma or urine and introduced to a column where
separation by physical characteristics takes place. (charge, size, polarity)
•Used to help diagnose:
- Carcinoid tumors
- Pheochromocytomas
- Neuroblastomas
- Not subject to hook effect and heterophile antibodies
- More labor intensive, more skill required
Methods of Tumor Marker Measurement -
Immunohistochemistry and Immunofluorescence
- Specific antibodies are incubated with tissue sections to detect the presence of antigens using colorimetric or fluorescent secondary antibodies.
- Specimens usually obtained through biopsy or fine-needle aspiration.
•Example of use:
•Estrogen and progesterone receptors in breast cancer
- If positive for estrogen and progesterone receptors - respond to hormonal therapy
- If lacking receptors - treatment with other chemotherapeutic agents
Methods of Tumor Marker Measurement - Enzyme Assays
•Detection of elevations of circulating enzymes can help identify a specific tumor or site of
tumor.
•Dying cells undergo changes in membrane permeability and release enzymes into
circulation.
- Examples:
- Alkaline phosphatase (ALP) - bone, liver, leukemia, sarcoma
- Lactate dehydrogenase (LD) - liver, lymphomas, leukemia
Types of Tumor Markers
Tumor markers include a wide variety of diverse molecules:
•Serum proteins
•Oncofetal antigens
- Proteins typically found during fetal development but that are found in adults with certain cancers
•Hormones
•Metabolites
•Receptors
•EnzymesEnzyme Tumor Markers
•Can be elevated nonspecifically in tumors.
- Increased due to high metabolic demand of proliferative cells
•Levels correlate well to tumor burden (# of cancer cells, size of tumor, etc.)
- Useful to monitor success of therapy
Serum Protein Tumor Markers
•Multiple Myeloma
- Immunoglobulins provide specific measure of plasma cell production of monoclonal proteins
Endocrine Tumor Markers
- Hormones and hormone metabolites are used as markers of secreting tumors.
- Useful for diagnosing:
- Neuroblastomas
- Pituitary adenomas
- Adrenal adenomas
Carbohydrate and Cancer Antigen Tumor Markers
Best used for monitoring treatment of tumors
Receptor Tumor Markers
Used to classify tumors for therapy
α-Fetoprotein (AFP)
- Oncofetal antigen
- Synthesized by fetal liver
-
****Elevated with hepatocellular carcinoma (HCC) and nonseminomatous testicular cancer
- Used to monitor therapy, detect residual tumor and detect relapse
•Analytic Methodology:
•Immunoassays
•Same laboratory and assay method should be used for serial monitoring
- (Changes due to tumor and not assay variation)
•AFP also used in maternal serum screen to detect neural tube defects and chromosomal abnormalities.
Human Chorionic Gonadotropin (hCG)
***Elevated in trophoblastic tumors
- Mainly choriocarcinoma and germ cell tumors of ovary and testis
•Occasionally elevated in ovarian and some lung cancers
Clinical applications:
•Prognostic indicator for ovarian cancer
•Diagnostic marker for classification of testicular cancer
•Detection of gestational trophoblastic diseases
Analytic Methodology:
•Immunoassays
•Use antibodies targeted towards epitopes in β-subunit and intact hCG
•Patients should be monitored using same technique each time.
•hCG assays are designed to detect pregnancy, not all equivalent for application as a tumor
marker
Use of AFP and hCG for Testicular Cancer Classification
•AFP and β-hCG can be used together in conjunction with biopsies to diagnose subtypes of
testicular cancer
Cancer Antigen 125 (CA-125)
*****Useful for detecting ovarian tumors and monitoring treatment.
- Patients with elevated levels after treatment have poor prognosis
- Not used to screen asymptomatic individuals.
- Recommended annual testing if family history or history of previous ovarian cancer
- Analytic Methodology:
* Immunoassays- Results from different platforms are not interchangeable
Carcinoembryonic Antigen (CEA)
•Oncofetal antigen
****Most widely used for colorectal cancer
•Can also be elevated in lung, breast, and gastrointestinal tumors
- Used to aid in diagnosis, prognosis, and monitoring of therapy for colorectal cancer.
- High levels of CEA are not specific for colorectal cancer, so not used for screening purposes.
- Analytic Methodology:
* Immunoassay
* Same method should be used for serial monitoring
Prostate-Specific Antigen (PSA)
•Low levels found in healthy men
***Used to screen and monitor prostate cancer
- Non-specific; also elevated in benign conditions
- Controversy over whether benefits outweigh the risks (biopsies)
- Screening should begin at age 50 (40-45 if at higher risk)
•Analytic Methodology:
•Immunoassay
- Hook effect and HAMAs have been known interferences
