Relationship between formalin reagent and success rate of targeted sequencing analysis using formalin fixed paraffin embedded tissues.

BACKGROUND

Tumor genetic alterations are determined to aid in selecting therapy and predicting prognosis. In routine clinical practice, targeted sequencing analysis is performed using formalin-fixed paraffin embedded (FFPE) tissues. However, successful genetic analysis remains challenging because FFPE DNA is fragmented during the sample preparation process.

METHODS

Real-time PCR was performed to assess DNA quality and quantities. Targeted sequencing was performed using FFPE tissues fixed with different types of formalin.

RESULTS

DNA was less fragmented from samples fixed in low formalin concentration (10% vs. 20%) and neutral buffered conditions (neutral buffered vs. non-neutral). DNA fragmentation increased over the fixation time. In a preliminary test study, we compared fixation using 10% neutral buffered formalin (n = 180) and 20% formalin (n = 26). The success rate of targeted analysis was higher using 10% neutral formalin (98.3%; 177/180) compared with 20% formalin (34.6%; 9/26). In a validation study with additional formalin-fixed paraffin embedded tissues fixed with 10% neutral buffered formalin (n = 860), we reproduced these results and achieved a high success rate for targeted sequencing analysis (98.4%; 846/860).

CONCLUSION

Our data show that 10% neutral buffered formalin is recommended for fixation of formalin-fixed paraffin embedded samples to achieve high success rate of targeted sequencing analysis.