Abstract:

Objective To explore the influences of storage status （original sample or genomic DNA） and time on the mutations of EGFR gene in non-small cell lung cancer （NSCLC）. Methods Ten fresh frozen tissues and 10 formalin-fixed paraffinembedded （FFPE） tissues of NSCLC harboring EGFR mutations were collected. During the twelve months after the first detection， DNA was drawn from fresh frozen tissues （new frozen extraction group） and FFPE tissues （new FFPE extraction group） at an interval of one month. The remaining genomic DNA from fresh frozen tissues （reserved frozen group） and FFPE tissues （reserved FFPE group） were chosen as control after the first detection. The detection kits were used to qualitatively and quantitatively measure the mutations of EGFR gene in four groups， and real time PCR was performed to quantify the Ct value of reference gene to reflect the contents of genomic DNA. The mutation frequencies of EGFR gene and Ct values of reference gene were compared among 4 groups. Results The mutation of EGFR gene could be detected in 20 tissues of original samples， which were consisting with the clinical data. The concentrations of DNA drawn from fresh frozen tissues and FFPE tissues were above 50ng／μl with A260／A280 around 1.8±0.2. The Ct values were high in the reserved frozen group versus the new frozen extraction group after 10 months （P＜0.05）. No significant difference of Ct value was observed between the new FFPE extraction group and the reserved FFPE group （P＞0.05）. The mutation frequencies of EGFR gene in the new frozen extraction group after 6 months and the new FFPE extraction group after 4 months were significant higher than those in the corresponding reserved group （P＜0.05）. Conclusion Original samples are better resources than reserved genomic DNA in retrospective studies.