Tumor Markers Flashcards
Cancer
- 2nd leading cause of mortality in developed countries
- 42% males and 38% females will develop invasive cancer in lifetime
- Lifetime risk of dying of cancer 23% male and 19% female
- Rates higher in marginalized groups (racial/ethnic/sexual orientation)
Cancer progression steps
- Proliferation
- Transformation
- Invasion
- Metastasis
- Vascularization (solid tumors)
Cancer staging
Stage 1: Epithelium with tumor cells
Stage 2: Invasion of primary tumor thru epithelium and into blood vessels
Stage 3: Migration of tumor into regional lymph nodes
Stage 4: Metastasis and invasion of tumor to distant tissues
Tumor marker
- Biomarker found in the blood or tissue and when elevated is linked to cancer
- Tumor produces it OR marker is effect of tumor on healthy tissue
- Examples: hormones, metabolites, receptors, enzymes, oncofetal antigens
Oncofetal antigen
Protein produced during fetal development and elevated in individuals with cancer
Enzyme tumor markers
- Elevated non-specifically
- Largely a result of high metabolic demand of tumor cells
- Tend to correlate with tumor burden
- Clinically useful for monitoring therapy success
List serum protein tumor markers
- Beta-macroglobulin
- Immunoglobulins
Beta-macroglobulin
- Found on surface of all nucleated cells
- Used as non-specific marker of the high cell turnover common in tumors
Immunoglobulins
- Multiple myeloma
- Provides relatively specific measure of plasma cell production of monoclonal proteins
Endocrine tumor markers
When used?
Diagnose what?
Examples?
- Used in endocrine malignancies
- Valuable in diagnosing neuroblastomas, pituitary, and adrenal adenomas
- Examples: ACTH, ADH, calcitonin, cortisol, PTH…etc
Oncofetal antigen tumor marker
- One of first classes of tumor markers
- Expressed transiently during normal development BUT turned on again in formation of tumors
- Ag: Carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP)
Carbohydrate and cancer antigen tumor markers
- Monoclonal defined antigens identified from human tumor extracts and cell lines
- There are Ab created to target specific carb or cancer Ag
- Best used for monitoring treatment of tumors that secrete these epitopes
Receptor tumor markers
Used for what?
Serological or non-serological?
Helps to do what in therapies?
- Receptors that are used to classify tumors for therapy
- Non-serological markers
- Helps to choose between endocrine and cytotoxic therapies
Ideal tumor marker traits
- Tumor specific
- Absent in healthy individuals
- Readily detectable in body fluids
List applications of tumor marker detection
- Numerous markers ID have high enough sensitivity AND specificity to aid diagnosis, prognosis, detection of recurrence, and/or monitoring response to treatment
- Used in combo with clinical signs, symptoms, and histology to facilitate clinical decision making
Screening and risk assessment
- Weigh benefits of disease detection vs harms of overtreatment (avoid false positives)
- No tumor marker can effectively screen asymptomatic populations
- Most found in normal and benign cells as well as cancer
- Targeted screening
- Family history of disease
Family history of disease for cancer
- ID germline mutations (breast, ovarian, colon)
- Breast and ovarian: BRCA1 and BRCA2
- Familial colon cancers: APC gene develop cancer by 40 by 99%
Prognosis
- [Tumor marker] generally increases with tumor progression
- Highest levels with metastasis
- Levels at diagnosis reflect aggressiveness, may predict outcome/indicate malignancy and metastasis
- Presence or absence may be valuable
- Can help determine best treatment options
T/F
Thyroid cancer is more common in men than women
False. More common in women than men
Monitoring effectiveness of therapy and disease recurrence
- Tumor marker levels can be used to help monitor therapy and can be followed serially
- Many tumor markers have lead time of several months vs other methods such as imaging
- Earlier indication of relapse
How does lack of standardization make comparison of serial tumor marker results difficult?
- Differences in Ab specificity
- Analyte heterogeneity
-Assay design - Lack of standardized reference material
- Calibration
- Kinetics
- Reference range variation
T/F
The wide range of tumor marker concentrations encountered clinically must be considered in the lab
True
List test methods for tumor markers
- Immunoassays
- HPLC
- Immunohistochemistry/immunofluorescence
- Enzyme assays
List specific tumor markers that are tested
- AFP
- Cancer Antigen 125 (CA-125)
- Carcinoembryonic Ag (CEA)
- Human Chorionic Gonadotropin (hCG)
- Prostate Specific Ag (PSA)
- CA-15-3
- Immunoglobulin Free Light Chains (FLC)
- Human Epididymis Protein 4 (HE4)
- Neuron-Specific Enolase (NSE)
Immunoassays
How common?
Advantages?
Unique factors?
- Common method
- Advantages: automated testing and ease of use
- Unique factors Assay linearity, Ag excess (hook effect), and potential for heterophile Ab
Immunoassay linearity
- Span of analytic concentrations over which linear relationship exists btwn analyte and signal
- Samples exceeding linear range much more likely with tumor markers
- Dilutions done: be careful of diluent used and be aware of calculation errors
Hook effect
- When analyte concentrations exceed the analytical range excessively (potential for Ag excess) such that you see decrease in signal at high analyte concentrations, so need to dilute analyte. Common in sandwich type assays
- Label Ab become saturated at high [Ag]
Heterophile Ab
- High interference in immunoassays
- These are Ab against reagents
- Subsets of heterophile Ab: human anti-animal, human anti-mouse
Common analytic concerns with tumor marker immunoassays
- Icterus (bilirubin)
- Lipemia
- Hemolysis
- Ab cross-reactivity
- Carry-over
HPLC
Function?
Extractions separated by which factors?
- Used to detect small molecules such as catecholamine metabolites in urine and plasma, endocrine metabolites. Detect hormones and metabolites secreted by tumors.
- Extractions separated by charge, size, and polarity
What are catecholamines and metabolites used to diagnose?
- Neuroblastoma
- Pheochromocytoma
- Carcinoid tumors
Neuroblastoma
- Common childhood malignant tumor
- High levels of plasma epinephrine, norepinephrine, and dopamine
Pheochromocytoma
- Rare tumor associated with hypertension
- Elevated plasma metanephrines, urine vanillylmandelic acid, free catecholamines
Carcinoid tumors
- Serotonin-secreting tumors from small intestine
- Serotonin metabolite (5-hydroxyindoleacetic acid)
HPLC advantages and disadvantages
Advantages:
- Not subject to hook effect
- No lot-to-lot variation
- No heterophile Ab interference
Disadvantages:
- More labor intensive
- More experience and skill required than automated
Immunohistochemistry/immunofluorescence
Sample type?
Sample collection method?
Method?
- Use solid tissue tumor markers not found in circulation
- Fine needle aspiration or biopsy
- Specific Ab incubated with tissue sections to detect Ag, colorimetric or. fluorescent secondary Ab
Enzyme assays
- Used before widespread use of immunoassays + oncofetal assays
- Most elevated enzymes can’t be used to specifically ID a type of tumor, but PSA is exception
- Examples: ALP, LDH, PSA
Alpha-fetoprotein (AFP)
What is it?
Synthesized where?
Expression pattern?
When is it elevated?
- Abundant serum carcinoembryonic protein
- Normally synthesized by fetal liver
- Re-expressed in certain types of tumors
- Often elevated in patients with hepatocellular carcinoma (HCC) and germ cell tumors
AFP regulation and physiology
- AFP is a glycoprotein related to albumin that normally functions as a transport protein
- AFP involved in regulating fetal oncotic pressure
- During development, AFP peaks at 1/10 albumin level at 30 wks gestation
- Infants: high levels that decline to adult levels at 7-10 mths old
AFP clinical usefulness and interpretation
- Used for diagnosis, staging, prognosis, and treatment monitoring of HCC
- AFP can be elevated in benign conditions such as pregnancy, non-malignant liver disease, other malignancy (testicular cancer)
Hepatocellular carcinoma (HCC)
- Tumor originating in liver
- Can be caused by chronic disease such as cirrhosis, hepatitis
- Elevated AFP (non-specific)
Testicular cancer
Subtypes:
- seminomatous: it forms directly from malignant germ cells
- nonseminomatous: differentiate into embryonal carcinoma, teratoma, choriocarcinoma, yolk sac tumors
T/F
AFP is used with hCG to classify nonseminomatous tumors
True
AFP methodology and clinical application
- Methodology: Automated immunoassays, Sandwich assays with mAb or poly-Abs
- Clinical app: primary tumor marker for HCC and nonseminomatous testicular cancer (monitor, detect residual tumor, or relapse). AFP part of maternal serum screening for neural tube defects and chromosomal abnormalities
CA-125
What is it?
Regulation and physiology?
- Murine mAb against serious ovarian carcinoma cell line
- Expressed in ovary/human ovarian carcinoma cells. May be elevated in patients with endometriosis, 1st tri of pregnancy, or during menstruation
CA-125
Clinical Usefulness?
Methodology?
- Serological marker for ovarian cancer
- Immunoassays use OC125 and M11 Ab on many different, non-interchangeable methods
CA-125
Clinical application
- Distinguish between benign masses and ovarian cancer
- Monitor therapy
- Evaluate pt response to treatment + predict current cancer
- Post-menopausal women with high levels and palpable mass, positive predictive value of 90%
- CA-125 can predict surgery success and efficacy of chemotherapy
- Elevated post-treatment means poor prognosis
CEA
What is it?
Regulation and physiology?
Functions?
Elevated in which demographic?
- It is a prototypical oncofetal Ag expressed during development and re-expressed in tumors. Most widely used for colorectal tumors but also found in lung, breast, and GI tumors
- It’s a large heterogenous glycoprotein part of Ig superfamily
- Functions in apoptosis, immunity, cell adhesion. May be involved in metastasis
- Increased CEA in heavy smokers and some pt following radiation treatment
CEA
Clinical usefulness?
Methodology?
Clinical applications?
- Main use as marker for colorectal cancer
- Immunoenzymatic sandwich assays, anti-CEA mouse mAb
- Used for surgical monitoring and chemotherapy
hCG
What is it?
Regulation and physiology?
- It’s a dimeric hormone secreted by trophoblasts and functions to promote implantation of blastocyte and placenta, maintains corpus luteum in 1st tri of pregnancy
- Elevated in trophoblastic tumors, choriocarcinoma, and germ cell tumors of ovary/testes
- Glycoprotein with alpha and beta subunits that is degraded into multiple fragments
- Intact or beta-hCG elevated in malignancies
- Most assays detect multiple hCG fragments
hCG
Clinical usefulness?
Methodology?
Clinical application?
- Prognostic for ovarian cancer and diagnostic for classification of testicular cancer
- Most useful marker for detection of gestational trophoblastic diseases
- Methods: Total beta-hCG assay most useful bc detects both intact and free beta-hCG
- Clinical app: Testicular cancer, elevated in pt with nonseminomatous
Prostatic Specific Ag (PSA)
What is it?
Function?
- It’s a glycoprotein produced in epithelial cells of the acini and ducts of the prostate gland
- Functionally regulates seminal fluid viscosity, and dissolves cervical mucus cap to allow sperm to enter
PSA regulation and physiology
- Healthy men have low circulating PSA levels
- Most circulating forms are bound
- Total PSA screens/monitors prostate cancer
- Detect total and free/unbound
PSA
Clinical use?
Methodology
Clinical app
- Informed decision-making, screening higher risk individuals (1st degree relative, black)
- Methods: Immunoassay, enzyme, fluorescence, chemiluminescence. Hook effect and heterophile Ab interference factors
- Clinical app: monitor prostate cancer/therapy, post-prostatectomy: serial PSA undetectable if cancer is localized
CA-15-3
Regulation and physiology?
Clinical usefulness?
Methodology?
Clinical app?
- Regulation: Mucin 1 transmembrane protein normally expressed in glandular or luminal epithelial cells. Encodes tumor assoc Ag CA 15-3 and CA27.29
- Clinical use: Manage breast cancer pts, early detection, response to therapy with metastatic breast cancer
- Methods: Immunoenzymatic sandwich assays
- Clinical app: Serial testing breast cancer pts
CA 19-9
Regulation and physiology?
Clinical usefulness?
Methodology?
Clinical app?
- Regulation: Modified Lewis (Le a) blood group Ag. But Le a-b don’t express CA 19-9 bc lack fucosyltransferase
- Clinical use: Pancreatic cancer, serial. Elevated in GI and benign malignancices
- Methods: Immunoenzymatic sandwich assays
- Clinical app: Best validated biomarker for pancreatic cancer
Pancreatic cancer caveat in relation to CA 19-9?
NOT ALL Lewis antigen negative pts with pancreatic cancer are non-secretors of CA 19-9
Immunoglobulin Free Light Chains (FLC)
Regulation and physiology?
Clinical usefulness?
Methodology?
Clinical app?
- Regulation: Multiple myeloma has increased levels, Waldenstrom macroglobulinemia (IgM), monoclonal Ig
- Clinical use: Serum protein electrophoresis look for M-spike. Calc kappa/lambda light chain ratios
- Methods: Serum kappa or lambda measured by nephelometry
- Clinical app: Minimizes neeed to quantitate/perform urine protein electrophoresis, baseline FLC gives diagnostic value in plasma cell dyscrasias, allows monitoring of patients previously thought to have non-secretory myeloma
Human epididymis protein 4 (HE4)
Regulation and physiology?
Clinical usefulness?
Methodology?
Clinical app?
- Regulation: Function unknown. Overexpressed in ovarian cancer
- Clinical use: Higher sensitivity for ovarian cancer detection than CA-125, part of risk for ovarian malignancy algorithm
- Methods: Immunoenzymatic sandwich assays
- Clinical app: Ovarian cancer, improved specificity over CA-125, latter of which can be elevated in endometriosis
Neuron-Specific Enolase (NSE)
Regulation and physiology?
- Enolase catalyzes 2-phosphoglycerate to phosphoenolpyruvate
- NSE predominant gamma isoenzyme.
- Present in RBCS - reject hemolyzed samples
- Measure in CSF or serum. - Differential diagnosis of neurodegenerative disorders
- Elevated in CSF may indicate Creutzfeldt-Jakob disease
Neuron-Specific Enolase (NSE)
Clinical usefulness?
Methodology?
Clinical app?
- Clinical usefulness: Follow-up marker or auxiliary test for small cell lung carcinoma, carcinoid tumors, pancreatic islet tumors, or neuroblastomas
- Methods: Homogenous immunofluorescent sandwich assay
- Clinical app: Auxiliary test for neuroendocrine tumors
