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Long-Term Storage of Plasma Causes DNA Degradation

Quality-control programs needed for future plasma DNA biomarker studies

TUESDAY, Dec. 20 (HealthDay News) -- DNA levels in whole plasma and purified plasma drop substantially in frozen storage, up to 30% annually, Italian scientists report in the Dec. 21 issue of the Journal of the National Cancer Institute. The finding could have an impact on clinical trials that assess levels of plasma DNA, they say.

Gabriella Sozzi, Ph.D., and colleagues from the Istituto Nazionale per lo Studio e la Cura dei Tumori in Milan, examined free circulating DNA levels in whole plasma and purified DNA using real-time polymerase chain reaction. The researchers examined two sets of patients: 34 lung cancer patients and 28 matched controls; and 117 cancer-free heavy smokers. Samples were stored frozen, with a median time between assessments of 41 months for the first group and nine months for the second group.

DNA levels in both plasma and isolated DNA samples dropped by about 30% per year in all patients.

The results "should be taken into account during planning and execution of large prospective clinical trials that involve the analysis of circulating plasma DNA or when stored plasma specimens are used for retrospective analyses that involve comparison of amounts of plasma DNA or detection of biomarkers in plasma DNA," Sozzi and colleagues conclude.

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