Address for correspondence: Dr. Dave S.B. Hoon, Department of Molecular Oncology, John Wayne Cancer Institute, 2200 Santa Monica Blvd., Santa Monica, CA 90404, USA. Voice: 310-449-5267; fax: 310-449-5282. hoon{at}jwci.org
Ann. N.Y. Acad. Sci. 1022: 17-24 (2004).
A variety of tumor-genetic alterations have been identified
circulating free-form in the plasma and serum of cancer patients
that may have diagnostic and prognostic implications. Currently,
no consensus exists as to whether plasma or serum is preferable
for circulating nucleic acid analysis, and the impact of collection
and processing on yield is unknown. We prospectively assessed
DNA content in paired plasma and serum obtained from 10 patients
with AJCC stage IV advanced metastatic melanoma. Blood (30 mL)
was collected from each patient as follows: 10 mL each was processed
immediately for serum and plasma and an additional 10 mL was
incubated overnight at 37°C and processed for serum. In
addition, blood was collected from 25 normal healthy donor volunteers
to determine the concentration of free DNA circulating in paired
plasma and serum. DNA was isolated from 800 µl of plasma
or serum and quantified. Median-free DNA concentrations were
fourfold greater in serum than in the corresponding plasma sample.
Serum isolated from blood allowed to clot overnight yielded
four times more DNA than serum processed immediately. Among
normal healthy volunteers, only serum contained detectable free
DNA. These findings provide conclusive evidence that elevated
levels of circulating DNA could be identified consistently in
patients with cancer than in normal healthy donors. Furthermore,
the method of blood processing may significantly affect the
levels of circulating nucleic acids and impact the investigator's
results. Significant consideration must be given to the methods
by which circulating nucleic acids are obtained for clinical
analysis.
