CANCER MARKERS: What
are they?? Suppose you think that your pt is having cancer somewhere in body
and therefore before U insist on some invasive U ask for some markers to
strengthen your diagnosis of invasive procedures or say prognosis after
definitive therapy Tumour marker is a substance present in or produced by a
tumour itself or produced by the host in response to a tumour from normal
tissue or to determine the presence of a tumour based on measurement in blood
or secretions. It is measured qualitatively or quantitatively by chemical
immunological or molecular methods to identify cancer presence . ideally tumour
marker should occur only inpatients with malignancy should correlate with stage
and response to treatment and should be easily and reproducibly measured. No
tumour marker has met this ideal yet. Tumor markers are either polypeptides
protein hormones surface antigens cytokines oncogenes or gene products.
Baseline levels measured prior to therapeutic intervention and followed later
by serial periodic measurements help to predict outcome of therapy. Tumour
markers also help in early detection of recurrence relapses and metastasis.
However it is the rate of change of the tumour marker level which is more
important than its absolute vale . These tests should not be used as a
screening test but should be correlated with other clinical criteria.
Clinical Applications- Mass
screening , differential diagnosis in symptomatic patients clinical staging
estimating tumour volume prognostic indicator of disease progression detecting recurrence evaluating the success
of treatment and monitoring response to therapy.
Recommendations for ordering Tumour
Marker tests :
Never rely on the result of a single test: Due
to nonspecificity associated with most tumour markers it may become difficult
to distinguish between malignant and benign disease on the basis of a single
test result. Levels within the normal range do not preclude the presence of
cancer nor are elevated results an absolute indication of malignancy . serial testing
is recommended because most elevations in benign diseases are transient whereas
in malignant diseases the level will remain elevated or rise continuously .
Test results should always be interpreted in conjunction with other clinical
and laboratory findings
1.
Serial testing should be
ordered from the same laboratory using the same assay kit: This is important in
order to ensure that changes observed in the tumour marker levels during the
monitoring process is caused by a change in tumour volume or other tumour
activities and not by laboratory variability because different commercial kits
can generate different results.
2.
Tumour marker selected
for monitoring recurrence must be elevated before surgery: No tumour marker is
100% sensitive to the detection of a particular type of cancer. Hence the
tumour marker selected to detect recurrence must be elevated before surgery.
Multiple markers should be measured prior to surgery in order to select the
tumour marker showing the highest elevation as the marker for monitoring
disease activity.
3.
Consider the half life
of the tumour marker when interpreting test result: Estimate the time required
for the level determined prior to surgery to decline to normal level based on
the known half life of the tumour marker e.g. half life of serum PSA is 3-4
days therefore it will take 30 days for as serum PSA at 50 ng/mL to drop to
undetectable levels following successful
surgery . It is preferable to wait one entire month before measuring the tumour
marker to assess the success of surgery because this is the time required for
the preexisting tumour marker in the serum to decline to lower levels.
4.
Consider how the tumour
marker is metabolized from blood circulation : Elevated serum tumour markers
are frequently seen in patients with
renal or liver disease depending on whether the tumour marker is removed through glomerular
filtration or metabolized by the liver e.g. serum CEA is often elevated in
patients with liver diseases because the impaired liver fails to remove CEA
from the blood circulation.
5.
Consider ordering
multiple tumour markers to improve sensitivity and specificity for diagnosis:
Multiple markers have been used to develop a more specific screening strategy
for ovarian cancer. It is found that the use of CA 15.3 and TAG 72 in
combination with CA 125 can increase the specificity to distinguish malignant
from benign disease. Multiple tumour markers that are complimentary to each
other should be selected and not those which run parallel to each other.
MARKER ASSOCIATED
CANCERS
Hormones
. hcg Trophoblastic
tumour , non-semino-
Matous
testicular tumour
. Calcitonin Medullary
thyroid carcinoma
. Catecholamines
And Metabolites Pheochromocytoma
Oncofetal Antigens
. AFP Hepatocellulr
carcinoma non seminomatous germ cell testicular
Tumour
. CEA Carcinomas
of colon , pancreas, lung, stomach and breast
Mucins and
Glycoproteins
.CA 125 Ovarian cancer
.CA 19.9 Pancreas and
colon cancer
.CA 72.4 Gastric and colon
cancer
.CA 15.3 Breast cancer
.Cyfra 21.1 Non small cell lung
cancer
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