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.
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.
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.
To 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.
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