tumor markers

Question 1

Cancer

Answer 1

uncontrolled growth of cells that often forms a solid mass or tumor that may spread to
other areas of the body.

stages 1- 4

Question 2

tumor markers

Answer 2

•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)

Question 3

Characteristics of “Ideal” Tumor Markers

Answer 3

• 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.

Question 4

Applications of tumor markers

Answer 4

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

Question 5

Applications of Tumor Markers - Screening

Answer 5

• 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

Question 6

Applications of Tumor Markers - Diagnosis

Answer 6

•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

Question 7

Applications of Tumor Markers - Prognosis

Answer 7

• 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.

Question 8

Applications of Tumor Markers - Monitoring

Answer 8

• 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.

Question 9

Preanalytical Requirements

Answer 9

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

Question 10

Laboratory Considerations for Tumor Marker Analysis

Answer 10

1. Size and variability of tumor marker concentration between different manufacturers
   •Hard to compare patient results if different assays are used
2. Wide range of concentrations encountered
   •Accurate measurement can be challenging
   •Ex. hCG can range between 10 and 10,000,000 mIU/mL

Question 11

Methods of Tumor Marker Detection

Answer 11

• Immunoassay
• High-Performance Liquid Chromatography
• Immunohistochemistry and Immunofluorescence
• Enzyme Assays

Question 12

Methods of Tumor Marker Measurement - Immunoassay

Answer 12

•Most common method to measure tumor markers
- Can be automated, easy to use

•Considerations with immunoassays include: linearity, hook effect, and heterophile antibodies

Question 13

Linearity ( immunoassays )

Answer 13

• 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)

Question 14

Hook Effect ( immuniassays )

Answer 14

• 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

Question 15

Heterophile antibodies ( immunoassays )

Answer 15

• 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

Question 16

Carryover ( immunoassays )

Answer 16

•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

Question 17

Methods of Tumor Marker Measurement - HPLC

Answer 17

•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

Question 18

Methods of Tumor Marker Measurement -

Immunohistochemistry and Immunofluorescence

Answer 18

• 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

Question 19

Methods of Tumor Marker Measurement - Enzyme Assays

Answer 19

•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

Question 20

Types of Tumor Markers

Answer 20

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
•Enzymes

Question 21

Enzyme Tumor Markers

Answer 21

•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

Question 22

Serum Protein Tumor Markers

Answer 22

•Multiple Myeloma

- Immunoglobulins provide specific measure of plasma cell production of monoclonal proteins

Question 23

Endocrine Tumor Markers

Answer 23

• Hormones and hormone metabolites are used as markers of secreting tumors.
• Useful for diagnosing:
  • Neuroblastomas
  • Pituitary adenomas
  • Adrenal adenomas

Question 24

Carbohydrate and Cancer Antigen Tumor Markers

Answer 24

Best used for monitoring treatment of tumors

Question 25

Receptor Tumor Markers

Answer 25

Used to classify tumors for therapy

Question 26

α-Fetoprotein (AFP)

Answer 26

• 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.

Question 27

Human Chorionic Gonadotropin (hCG)

Answer 27

***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

Question 28

Use of AFP and hCG for Testicular Cancer Classification

Answer 28

•AFP and β-hCG can be used together in conjunction with biopsies to diagnose subtypes of
testicular cancer

Question 29

Cancer Antigen 125 (CA-125)

Answer 29

*****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

Question 30

Carcinoembryonic Antigen (CEA)

Answer 30

•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

Question 31

Prostate-Specific Antigen (PSA)

Answer 31

•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