Effect on DNA stability of a novel pellet storing method for liquid-based cytology specimens fixed using an alcohol-based preservation solution: Studies using EGFR mutation detection on a lung adenocarcinoma cell line.

Introduction: Liquid-based cytology (LBC) specimens of lung cancer are increasingly being used for genetic analyses. Preservation conditions of specimens until DNA extraction are important because they can affect DNA quality. We investigated whether a novel method of storing residual LBC specimens as pellets using an alcohol-based preservation solution would improve DNA stability.

Methods: Lung adenocarcinoma cell line cells fixed in PreservCyt® solution were either stored using the conventional method (suspended in PreservCyt®; Susp group) or washed in phosphate-buffered saline and stored as cell pellet (novel method; cell pellet [CP] group). We analyzed the DNA quality of the cells after storage at ambient temperatures for 7, 14, and 28 days and compared DNA stability in dry cell pellets (d-CP) versus wet cell pellets (CP) after 7 days of storage. DNA stability was evaluated based on epidermal growth factor receptor mutation detection efficiency using the Cycleave PCR method.

Results: The dsDNA yield and DNA integrity number (DIN) in the CP group were significantly higher than those in the Susp group at all time points. However, the UV absorbance of DNA from the CP group was lower than that from the Susp group. Mutation detection analysis indicated that DNA from the CP group had significantly lower Ct values than that from the Susp group on days 14. The DIN of DNA from the d-CP group was comparable to that from the CP group; however, the dsDNA yield in the d-CP group was reduced to less than half.

Conclusion: The storage of LBC specimens as cell pellets after fixation in alcohol-based preservation solutions offers improved DNA stability and is a promising strategy for genetic analysis.