The effect of storage duration on the preservation of DNA and the feasibility of genetic studies in formalin-fixed paraffin-embedded tissue samples

Objective. To determine the concentration of isolated DNA from archived paraffin blocks of cervical cancer using real-time PCR and to study its relationship with the storage period of samples. Material and methods. DNA was extracted from paraffin blocks of 62 cervical cancer samples using a commercial DNA extraction kit (BioLink LLC, Russia). The amount of HER2/neu gene DNA extracted was assessed by real-time PCR using the Real-time-PCR-HER2/neu kit (BioLink LLC, Russia) according to the manufacturer’s instructions. All samples were divided into 3 groups depending on the storage period of the paraffin blocks: group 1 (0—5 years), group 2 (5—8 years), group 3 (8—10 years). Results. The concentration of DNA extracted from paraffin blocks of cervical cancer stored for 0—5 years was 10.00 ng/μl [2.70—10.00], which is statistically significantly higher than the values obtained for blocks stored for 5-8 years (0.20 ng/μl [0.20—0.40]) and 8—10 years (0.20 ng/μl [0.20—0.20]) (P=0.019631 and P=0.000003, respectively), no significant differences were found between samples stored for 5-8 years and 8-10 years. When studying the dynamics of DNA concentration over time in groups with storage periods of 0-5 years and more than 5 years, a decrease of 9.80 ng/μl (98.0%) (p<0.01) was detected. Conclusion. The concentration of extracted DNA from paraffin blocks of cervical cancer significantly decreases over time and reaches threshold values after more than 5 years of storage, which must be taken into account when planning retrospective study.