Circulating Tumor Markers: Basic Concepts and Clinical Applications (F) Flashcards
What is the 2nd leading cause of death in developed countries?
Cancer (CA)
True or False
CA accounts for less than 2.7 M deaths annually
False, because CA accounts for more than 2.7 M deaths annually
What is CA (what is its principle)?
It is the uncontrolled growth of cells that can develop into a tumor & spread to other areas of body
What is the cause of formation and spreading (metastasis) of tumors?
Complex combination of inherited & acquired genetic mutations
In terms of the formation of CA, mutations include what?
Activation of:
1) Growth factors
2) Oncogenes
3) Inhibition of apoptosis
4) Tumor suppressor
5) Cell cycle regulation genes
CA is staged based on what?
1) Tumor size
2) Histology
3) Regional lymph node involvement
4) Presence of metastasis
How many are the stages of CA?
4 stages
What are the stages of CA?
1) I
2) II
3) III
4) IV
What are the events that happen in CA staging and progression?
1) Stage I
- > localized primary tumor
2) Stage II
- > invasion of primary tumor through epithelium and into blood vessels
3) Stage III
- > migration of tumor into regional lymph nodes
- > happens in the liver
4) Stage IV
- > metastasis and invasion of tumor to distant tissues
- > happens in the lung and liver
What are the fxns of tumor markers?
1) Detect and 2) monitor CA
What is the origin of tumor markers?
These are produced by tumor directly or as an effect of tumor on tissue
What are the types of tumor markers (include its principle and exs)?
1) Enzymes
- > levels of certain enzymes correlate w/ tumor burden
2) Serum proteins
- > such as β2-microglobulin & immunoglobulins
3) Hormones & metabolites
- > such as sp. markers of secreting tumors
4) Oncofetal antigens
- > such as carcinoembryonic and alpha-fetoprotein
5) Receptors
- > non-serologic
- > such as estrogen and progesterone receptors
What is the timeline of tumor marker use (include the tumor markers and the utility for each stage of the timeline)?
Screening
-> utility: biopsy indication
-> tumor marker: PSA
Diagnosis
-> utility: high lvls indicative of disease
-> tumor markers: metanephrines, HVA/VMA, prolactin, PTH, chromogranin A, cortisol, and ACTH
Prognosis
-> utility: high lvls associated w/ poor px; receptor status used for indication of chemotherapy
-> tumor markers: β2-Microglobulin, CA-125, CEA, LD, Her-2/neu, ER, and PR
Monitoring treatment
-> utility: monitor efficacy of chemotherapy; residual disease after surgery
-> tumor markers: CA-125, CA 19-9, CEA, AFP, hCG, PSA, and SPE
Detection of recurrence
-> utility: increased associated w/ relapse
-> tumor markers: CA 15-3, CA-125, CEA, AFP, hCG, and PSA
Screening -> Dx -> Px -> Monitoring treatment -> Detection of recurrence
Time element towards detection of recurrence from screening
What are the applications of tumor marker detection?
1) Screening
2) Px
3) Monitoring therapy effectiveness & disease recurrence
What is the principle of screening (as an application of tumor marker detection)?
Most tumor markers are found in normal cells, not just CA cells
Therefore, screening asymptomatic populations would result in detection of false (+)s, causing undue alarm and cost
True or False
All tumor markers are used to screen populations
False, because few tumor markers are used to screen populations
How can the susceptibility to breast, ovarian, and colon CA be determined?
These can be determined by identifying germline mutations in pts w/ a family history of these diseases
Breast and ovarian CAs are associated w/ what?
Germline BRCA1 and BRCA2 mutations
Colon CA is associated w/ what?
Adenomatous polyposis coli gene (APC)
In relation to px (w/c is 1 of the applications of tumor marker detection), tumor marker conc. gradually increases w/ what?
Tumor progression (reaching highest lvls when tumor metastasize)
Tumor marker lvls at dx can reflect what?
1) Presence of malignancy
2) Aggressiveness of tumor
3) Help predict outcome
In relation to monitoring therapy effectiveness and disease recurrence (w/c is 1 of the applications of tumor marker detection), when are the situations where tumor markers are observed?
After:
1) Surgical resection
2) Radiation
3) Chemotherapy
Effective therapy can result in what?
Decrease in tumor markers
Appearance of tumor markers after effective therapy can be used as what?
As a highly sensitive marker of recurrence
What are the lab considerations for tumor marker measurement?
1) Multiple tests should be performed (using same commercial kits)
2) Lack of standardization
3) Serially evaluate tumor markers (because they increase w/ time, whereas high normal values will not)
True or False
Standardization found for other common clinical assays generally does not exist for CA assays
True
Comparisons of results from different assays for a single pt can be treacherous due to differences in what?
1) Ab specificity
2) Analyte heterogeneity
3) Assay design
4) Lack of standard reference material
5) Calibration and kinetics
6) Variation in reference ranges
What are the methods for tumor markers?
1) Immunoassays
2) High-Performance Liquid Chromatography (HPLC)
3) Immunohistochemistry (IHC)
4) Enzyme assays
What is the most commonly used method to measure tumor markers?
Immunoassays
What is the characteristic of immunoassays?
It have many advantages (including ability to automate testing)
What are the factors in interpreting tumor marker immunoassays?
1) Linearity
2) Hook effect
3) Heterophile Abs
What is linear range?
It is the range of analyte concs. in w/c a linear relationship exists between analyte and signal
How is linearity measured (in connection to immunoassays)?
It is measured by analyzing sxs spanning reportable range
What is hook effect?
It is the falsely low measurements as a result of excessively high tumor marker concs.
What is the principle of hook effect?
Capture and label Abs are saturated, resulting in a lack of a “sandwich” formation, resulting in decrease in signal
In relation to hook effect, what should be done to sxs exceeding linear range?
These should be diluted and retested
What are heterophile Abs?
These are circulating Abs against animal Igs
What is the action of heterophile Abs?
These can cause significant interference in immunoassays
To whom are heterophile Abs occur?
These occur in pts given mouse monoclonal Abs
What are the uses of HPLC?
It is the most widely used method to detect:
1) Catecholamines (and their metabolites in plasma and urine)
2) Neuroblastoma
3) Pheochromocytoma
4) Carcinoid tumors
What is the principle of HPLC?
Analytes of interest are separated from plasma or urine, run over a column, and separated by physical characteristics
In IHC, how are tests tumor markers detected?
These are detected directly within solid tissue
What is the principle of IHC?
Slice of tissue is placed on glass slide and incubated w/ sp. Abs in solution to detect presence of Ags
What is the principle of enzyme assays?
Detection of elevated circulating enzymes generally cannot be used to identify a sp. tumor or site of tumor
What is the enzyme w/c is used as tumor marker that is exempted for enzyme assays?
Prostate specific antigen (PSA)
Where is PSA exclusively found?
In diseased and benign prostate glands
True or False
Before use of immunoassays and oncofetal Ags was common, enzyme detection was widely used
True
What are the exs of enzymes used as tumor markers (in enzyme assays)?
1) Alkaline phosphatase (bone, liver, leukemia, and sarcoma)
2) Creatine kinase-BB (prostate, small-cell lung, breast, colon, and ovarian)
3) Lactate dehydrogenase (LDH) (liver, lymphomas, and leukemia)
4) PSA (prostate)
What are the frequently ordered tumor markers?
1) Alpha-Fetoprotein (AFP)
2) Cancer Antigen 125 (CA-125)
3) Carcinoembryonic Antigen (CEA)
4) Human Chorionic Gonadotropin (hCG)
5) Prostate Specific Antigen (PSA)
What is AFP?
It is an abundant serum protein synthesized by fetal liver and re-expressed in certain types of tumors
To whom are AFP often elevated?
In pts w/:
1) Hepatocellular carcinoma
2) Germ cell tumors
AFP is a 70-kd glycoprotein related to what?
Albumin
What are the fxns of AFP?
1) It normally fxns as a transport protein
2) It is involved in regulating oncotic pressure in fetus
What is the upper limit of normal for serum AFP?
~ 15 ng/mL in adults
What are the clinical applications of AFP?
1) It is used for dx, staging, px, and treatment monitoring of hepatocellular carcinoma
2) It is also used for classification and monitoring therapy for testicular CA and for tumor staging
How is AFP measured?
It is measured by / via a variety of immunoassays
What are the uses CA-125?
1) It may be useful for detecting ovarian tumors at an early stage
2) It may also be useful for monitoring treatments w/out surgical restaging
Where is CA-125 expressed?
1) Ovary
2) Other tissues of müllerian duct origin
3) Other tissues of ovarian carcinoma cells
What is the clinical application of CA-125?
It is the only clinically accepted serologic marker of ovarian CA
What is the methodology for CA-125?
Immunoassays using “OC 125” and “M11” Abs
When is CEA discovered?
1960s
What is CEA?
It is a prototypical ex of oncofetal Ag
When is CEA expressed?
During development and re-expressed in tumors
What are the uses of CEA?
1) It is most widely used tumor marker for colorectal CA
2) It is elevated in:
a. Lung tumors
b. Breast tumors
c. GI tumors
What are the characteristics of CEA?
1) It is a large heterogenous glycoprotein
2) It has a MW of ~ 200 kDa
CEA is involved in what?
1) Apoptosis
2) Immunity
3) Cell adhesion
What are the clinical applications of CEA?
1) It is a tumor marker for colorectal CA
2) It is used for px
3) It is used for post-surgery surveillance
4) It is used to monitor response to chemotherapy
True or False
In terms of methodology, for CEA, polyclonal Abs are historically used, but now, monoclonal anti-CEA Abs are used
True
Due to high heterogeneity of CEA, what is essential?
It is essential that same assay be used for serial monitoring
What is hCG?
It is a dimeric hormone secreted by trophoblasts in placenta
What is the action of hCG?
To maintain corpus luteum during pregnancy
What are the characteristics of hCG?
1) It is a 45-kd glycoprotein
2) It consists of alpha and beta subunits
What are the clinical applications of hCG?
1) Px of ovarian CA
2) Dx of testicular CA
3) It is the most useful marker for gestational trophoblastic diseases
What is the methodology for hCG?
1) Immunoassays w/ monoclonal capture
2) Tracer Abs
What are the characteristics of PSA?
1) It is a 28-kd glycoprotein
2) It is produced only in epithelial cells of acini and in prostatic ducts
What are the actions of PSA?
1) It regulates seminal fluid viscosity
2) It dissolves cervical mucous cap (allowing sperm to enter)
Where can low lvls of PSA be detected?
In serum of healthy men
What are the 2 major forms of PSA found circulating in the blood?
1) Free
2) Complexed
What is the clinical application of PSA?
Annual screening of prostate CA in men over 50 yo and in younger men at high risk (family history)
What is the normal range for PSA?
< 4 ng/mL
What are the factors to take into account when testing for PSA?
1) Age
2) PSA velocity
3) Free PSA / total PSA ratios
How is PSA measured?
It is measured by / via immunoassay using:
1) Enzyme
2) Fluorescence
3) Chemiluminescence
4) Automated immunoassay platform
