Clinical Chem Proteins & Tumour Markers

# Learning outcomes

* To understand the importance of plasma proteins in the human body
* To know and understand the clinical relevance of plasma protein test for diagnosis of diseases
* To understand the uses of tumor marker in cancer diagnosis
* To describe patient management and the use of tumor markers in colon and breast cancers

# Plasma Proteins

Two major groups: albumin & globulins

Individual plasma protein conc affected by:

* nutritional status
* physiologic changes
* synthesis rate
* extracellular distribution
* clearance rate

Most synthesized in the liver, except immunoglobulins & protein hormones

## Prealbumin (Transthyretin)

* ^^**small transporter protein**^^ that migrates before albumin in classic serum protein electrophoresis
* ^^**transports thyroid hormones**^^
* also binds to retinol-binding protein for the ^^**transportation of vitamin A (retinol)**^^
* synthesised in the liver & choroid plexus of the central nervous system
* stimulated by glyuocorticoid hormones, androgens & NSAIDs
* [[**Laboratory Investigations**[[
* immunonephlometry
* immunoturbidimetry
* Clinical revelance
* indicates protein nutrition
* higher than normal: severe renal failure, corticosteroid use, oral contraceptive use
* lower than normal: malnutrition, liver disease, serious infection, trauma, inflammation, serious or long term illness, hyperthyroidism

## Albumin

* small protein found in blood, CSF, interstitial fluid, urine & amniotic fluid
* synthesised in liver:
* stimulated by hormones, e.g. insulin, cortisol & growth hormone
* inhibited by proinflammatory substances
* regulated by colloidal osmotic pressure and protein intake
* catabolised mainly in the muscle, liver & kidneys
* Primary function:
* maintain the colloidal osmotic pressure in the intravascular & extravascular compartments
* serves as a transport protein for fatty acids, phospholipids, cholesterol, amino acids, hormones, bilirubin, drugs, toxins, metallic ions & gas
* Laboratory investigations
* measured colorimetrically by using bromocresol green dye
* Clinical relevance
* related to liver or kidney disease, or underlying nutritional deficits
* hyperalbuminemia: dehydration, increased insulin level, blood transfusion, exogenous albumin administration, anabolic steroid use, androgen / growth hormone administration
* hypoalbuminemia: overhydration, hepatic disease, nephrotic syndrome, protein losing states, inflammation, poor nutrition

## α2-Macroglobulin

* serine protease inhibitor
* inhibits different types of proteinases
* inhibits enzymes in the kinin, complement, coagulation & fibrinolytic pathways
* carrier protein for cytokines, growth factors & cations
* modulates immunologic & inflammatory reactions
* very large glycoprotein synthesised mainly in the liver
* Laboratory investigations
* serum protein electrophoresis
* immunologic assay
* Clinical Relevance
* increased level: nephrotic syndrome, related to estrogen & age
* decreased level: acute phase response, pancreatitis, prostate cancer

## Immunoglobulins

* functions as antibodies
* Laboratory investigations
* serum protein electrophoresis
* immunoelectrophoresis
* immunoturbidimetry
* Clinical relevance
* Immunoglobulin deficiency
* most manifest in infancy
* those in adults are due to another primary disorder or immunosuppresive therapy
* most common types: selective IgG immunodeficiency, selective IgA immunodeficiency, X-linked agammaglobulinemia

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* Polyclonal hyperimmunoglobulinemia
* the blood level of all immunoglobulins is increased
* sometimes, a particular immunoglobulin is increased more compared to others
* autoimmune diseases → particularly IgG
* primary biliary cirrhosis → particularly IgM
* acute hepatitis → particularly IgG

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* Monoclonal immunoglobulinemia
* involves only one specific type of immunoglobulin
* increased concentration due to increased size of a particular clone of plasma cells (sharp peak on serum protein electrophoresis)
* multiple myeloma (plasma cell cancer)
* IgG (most common), followed by IgA & IgD; IgM
* malignant plasma cells secrete M proteins


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# Tumour Markers

Production:

* directly by the tumours; or
* as an effect of the tumours on healthy tissue; or
* other cells of the body in response to cancer

Traditional concept on tumour markers:

* proteins or other substances that are present at a higher amount in cancers
* found in blood, urine, stool, tumours, or other tissues & body fluids of cancer patients

## Carcinoembryonic Antigen (CEA)

* ]]expressed in embryonic tissue of gut, pancreas & liver]]
* elevated level in many different types of cancer
* 60-90% of colorectal carcinoma
* 50-80% of pancreatic carcinoma
* 25-50% of gastric and breast carcinoma
* also elevated in several benign disorders, i.e., alcoholic cirrhosis, hepatitis & ulcerative colitis
* lacking sensitivity & specificity for early detection of cancers
* Tumour burden
* CEA is measured before and after surgical resection to confirm successful removal of tumour burden
* Monitor the efficacy of treatment
* CEA should drop within the reference interval in 1-4 months if the treatment is successful
* Detect recurrence - serially monitored every 2-3 months

## α1-fetoprotein (AFP)

* major glycoprotein in fetal plasma
* serum level declines rapidly after birth; undetectable level within several months after birth
* synthesised by embryonic yolk sac and fetal liver
* produced and secreted by certain malignant tumours
* utilised as tumour marker
* Elevated level in adult males and non-pregnant females
* hepatocellular carcinoma, germ cell tumours, ovarian tumours
* Diagnosis
* clearly, marked elevation of α1- fetoprotein level + presence of liver mass
* Prognostication
* elevated level indicates aggressive tumour & poor prognosis in hepatocellular carcinoma
* Normally detected in maternal serum, and peaks at 12-15 weeks of pregnancy
* prenatal surveillance - elevated in neural tube defects
* part of triple or quadruple screening test for fetal abnormalities
* Non-cancerous conditions, e.g., hepatitis & liver cirrhosis, also reports an elevation in α1- fetoprotein level

# Tumour Markers (pt 2)

Important characteristics:

* tumour-specific
* absent in healthy individuals
* readily detectable in body fluids

5 broad uses:

* screening
* diagnosis
* prognosis
* treatment outcome prediction/monitoring treatment
* relapse

## Screening

Current widely-used screening methods

* mammography, cytology, fetal occult blood test

Serum tumour markers

* lack of sensitivity or specificity
* high proportions of false negatives/positives
* may be elevated in chronic inflammation or those without cancers
* usually elevated when the cancer is already well-establish

## Diagnosis

Ideally, the sensitivity & specificity should approach 100%

To date, none of the serum tumour markers reach this level of diagnostic performance

* poor diagnostic indicator

Gold standard - histology

## Prognosis

Concentration level of tumour markers increases with tumour progression

May reflect the aggressiveness of tumour and predict outcome

May reflect the size of tumour and predict survival

## Determination & monitoring of treatment

Presence or absence of tumour marker indicates the responsiveness towards a particular treatment

* determine the most suitable treatment approach

Monitor the efficacy of therapy

* after surgical resection, radiation, chemotherapy or targeted therapy
* direct quantitative relationship between tumour marker concentration and tumour load

Criteria used to assess effectiveness of treatment:

* no change: tumour marker >50% of value at t=0
* improvement: tumour marker