Biology Reference
In-Depth Information
6.
Sample collection, handling, and storage
whatever is shed, leaked, or secreted from the
tumor will be found in the urine. Also, the amount
of urine produced in 24 hours is less than the
amount of blood circulating in the body, so the
“
7.
Method of sample analysis
Each of these steps should be given a careful
consideration prior to the initiation of any study.
are more diluted in blood
than in urine. Blood contains larger amounts of
proteins than urine, making it a much more
complicated sample to characterize. Also, blood
contains albumin, which makes the analysis of
the blood proteome dif
biomarker molecules
”
Cancer Type and Stage
The
first step in any search for a biomarker is
to decide which disease condition to study. In
this chapter, the discussion is limited to cancer
because it is a very complicated and devastating
disease that affects millions of people of all ages,
genders, and ethnicities. Also, early detection of
cancer means a higher survivor rate and less
suffering. The decision is therefore to decide
which cancer type to study and whether to
analyze all stages together as one experiment
or each stage separately. It is preferable to
conduct the experiment on each stage separately
in order to
cult and can mask low-
abundance proteins, and its removal may cause
the loss of interacting proteins. The best sample
for a successful search of a biomarker for a solid
tumor, although invasive and not easily accessible,
is tumor tissue and its adjacent normal tissue.
Careful consideration should be given to
blood specimen analysis (i.e., whether the blood
sample should be converted to serum or plasma
prior to analysis). Serum and plasma are not
directly comparable in a proteomic analysis.
14,15
As mentioned, serum and plasma cannot be
directly compared in a proteomic study because
their protein pro
find out at what stage the biomarker
(protein or metabolite) can be detected.
les differ.
16
Another difference
between serum and plasma is that plasma is the
liquid portion of unclotted blood that is left
behind after all the various cell types are
removed. To prepare plasma, blood is with-
drawn from the patient into a vial in the presence
of an anticoagulant and the sample is centrifuged
to remove cellular elements. The most commonly
used anticoagulants include heparin, ethylene-
diaminetetraacetic acid (EDTA), and sodium
citrate. Serum is blood plasma without
Sample Type
After the decision has been made as to which
cancer and stage to study, the next decision is
related to the type of sample: tissue, blood, urine,
cells, or other
fluid. An important objective of
biomarker research is to
find a biomarker using
a noninvasive (e.g., urine, tears, saliva, etc.) or
minimally invasive (e.g., serum, plasma, etc.)
sample and to avoid, if at all possible, using inva-
sive procedures (e.g., tissue, cerebrospinal
fibrinogen
or the other clotting factors. It is prepared by col-
lecting blood in the absence of any coagulant.
Under these conditions, a
fluid,
etc.). Aliterature searchof thebiomedical literature
indicates that the most commonly used samples
for cancer biomarker discovery are urine, blood
(serum and plasma), and tissues.
13
Blood is prefer-
able to urine because blood
fibrin clot forms. This
clot is then removed using centrifugation, leaving
behind serum.
17
Removal of the clot results in
lower protein content in serum than plasma.
ows throughout the
body and its composition is stable and re
ects
the state of the patient at the time of collection.
Although urine is easily accessible, its composition
is subject to variation and dilution. Urine is prefer-
able, however, when studying bladder cancer,
especially transitional cell carcinoma, because
Selection of Patients and Controls
Subjects selected for a study should be checked
by a physician to ensure the presence or absence
of
the disease. Tissue samples
should be
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