Abstract 3760: The importance of optimizing DNA extraction conditions for formalin fixed paraffin embedded tissues

Abstract The pre-analytic extraction of Formalin Fixed Paraffin Embedded Tissues (FFPETs) appears to have a profound effect on the ability to obtain meaningful data from the DNA therein. FFPETs represent important materials in Pathology that are used to diagnose and analyze cancer. As part of preparing FFPETs, the formalin fixation step preserves the structure of tissues through covalent modifications but can also damage nucleic acids through that same process. Over the last decade, the emergence of Molecular Pathology, which benefits from gentler fixation compared to Histopathology and especially Immunohistopathology, has led to changes in how FFPETs are prepared. However, the remnant FFPETs from over a decade ago may be far from representative of what is now prepared for Molecular Pathology by many laboratories. Here we discuss our optimization of FFPET extraction for gently fixed samples. When we prepared our Seraseq FFPE Homologous Recombination Deficiency (HRD) reference standards using fixation conditions that are recommended for Molecular Pathology and extracted the resulting FFPETs using generic conditions, our initial coverage data from Whole Genome Shotgun (WGS) sequencing was difficult to analyze for changes in copy number across the genome. A major contributor to nonuniform coverage was identified as the formalin reversal step, where deparaffinized proteinase K-digested tissue is heated in water to near boiling to attempt to detach formaldehyde from nucleic acids through hydrolysis. Given the gentler fixation conditions, this step was found to be mostly unnecessary, and omitting it improved the resulting data substantially. A reason for this appears to be that the gentler fixation conditions that are now in use may not protect the DNA from the effects of near-boiling water, where the lack of salt lowers the melting temperature of double stranded DNA fragments and causes them to denature unless they have a higher GC content. Different kits used for the extraction of nucleic acids from FFPETs may benefit from different optimizations to obtain improved sequencing data from today’s Molecular pathology samples, and reference standards that represent such samples provide a useful tool for such optimizations. Citation Format: Matthew G. Butler, Benedicta Forson, Maria Cowen, Jayanthi Ramprakash, Dana Ruminski Lowe, Yves Konigshofer. The importance of optimizing DNA extraction conditions for formalin fixed paraffin embedded tissues abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3760.