What are the potential advantages of using tumor markers?
Although tumor markers are usually imperfect as screening tests for detection of occult
(hidden) cancers, once a particular tumor has been found using a marker, the marker
may be a way of monitoring the success (or failure) of treatment.
The tumor marker level may also reflect the extent (the stage) of the disease,
indicating how quickly the cancer is likely to progress and helping to determine the
prognosis (outlook).
Rising levels on test results can be, but are not always worrisome. Although changes
in tumor marker levels may be cause for alarm, other non-cancerous diseases can
cause test results to vary. Conditions in the lab that processes tests may also alter
the results.
Patients should always talk to their oncologist about their test results and keep
asking questions until they understand how these results will impact their prognosis
and treatment plan.
Advantages of using tumor markers include:
Early detection
- Providing more information about the disease to allow for tailored treatments
to be used, resulting in improved efficacy and survival
- Avoiding side effects from having unnecessary treatments
- Offering less invasive diagnostics
- Improving quality of life, and
- Reducing costs
What are the potential disadvantages of tumor markers?
Being able to deduce diagnostic patterns that are unique to specific cancer states is a
challenge because of the biological variability in an individual patients sample, as
well as the huge range of biomarker concentrations in all patients compared.
Differences in sample collection, handling or storage, and profiling techniques
among various research sites may change the protein profile obtained from a given
sample. Therefore, standardization issues regarding biological variation, preanalytical
variables and analytical variability must be tackled before standard values
can be established.
A major problem in the identification of cancer biomarkers is the very low
concentrations of markers obtained from tissues with small, early-stage cancer
lesions.
Other Problems Include:
- Lack of reliability
- Proteins and/or modified proteins may vary among individuals, between cell
types, and even within the same cell under different stimuli or different
disease-states. So it is difficult to know which value obtained from an
individual is accurate and what value in different patients indicates a problem.
- Normal cells as well as cancer cells can produce most tumor markers.
- Tumor markers are not always present in early-stage cancers.
- Tumor markers can be present because of noncancerous conditions.
- People with cancer may never have elevated tumor markers in their blood.
- Even when tumor marker levels are high, they are not specific enough to
confirm the presence of cancer.
The following comments are excerpts from the case study:
PSA Testing: Yes, No, Maybe?
Recent Research, Guideline Updates Add to Controversy
By Gina Rollins
"PSA is found in normal prostate tissue and at elevated levels when the gland is
inflamed. Since PSA is not specific to prostate malignancy, a diagnosis of prostate
cancer based on rising PSA serum levels results in a high rate of false positives-up
to 75% according to some studies. False positive values are highly undesirable
because they trigger costly, invasive medical interventions that divert healthcare
resources that could be better spent.
Biopsies of 100 suspected prostate cancer patients with PSA readings of 3 ng/mL or
higher will yield only 25 confirmed cases. In addition, 40% of PSA-negative readings
are false negative. The FDA approved PSA testing at a time when prostate cancer
diagnostics were essentially nonexistent. Were the PSA test to come up for regulatory
review today, it is unlikely it would be approved for use in prostate cancer screening.
Diagnostic tests that are approved for a single purpose are often used in situations
for which the test was not designed. The PSA test is a prime example. PSA was
originally approved in 1985 as a test to detect the recurrence of prostate cancer in
men who had been previously treated for the disease with radiation or surgery.
Today the test is routinely prescribed as a screening tool despite the fact that
evidence linking PSA testing to improved outcomes is lacking."
