Enhancement of pathologist's routine practice: Reuse of DNA extracted from immunostained formalin-fixed paraffin-embedded (FFPE) slides in downstream molecular analysis of cancer

Background/Aim: To date, the conventional formalin-fixed, paraffin-embedded (FFPE) technique is the gold-standard for preserving histomorphology. Once FFPE tissues are stained, slides are routinely archived along with their blocks at biobanks/hospitals. However, the reuse of fixed and stained biospecimens as DNA source is not a common routine practice worldwide and, thus, indicates the need of studies to investigate the feasibility of extracting DNA from already immunohistochemistry (IHC) FFPEstained slides and its possible reuse in subsequent downstream molecular analyses. Materials and Methods: FFPE IHC slides from colorectal cancer (CRC) patients were prepared and stored in the CEGMR Biobank. The workflow consists of digitalization of IHC stained slide's image, removing the slide cover-slip, crude dissection and DNA extraction. Following DNA quality assessment, mutation analysis of CTNNB1 and methylation profile of CDH1 were performed. Results: High-quality DNA was obtained allowing 60% concordance between CDH1 methylation and membranous E-cadherin expression pattern. Clean CTNNB1 DNA chromatograms with evenly-spaced peaks were observed. Conclusion: This study is a proof of concept to recycle and reuse DNA from IHC stained slides with suitable concentration and integrity for further downstream molecular applications. These findings will enhance the pathologists' knowledge, attitudes and practices (KAP) towards the use of these biospecimens and support the implementation of this approach in clinical pathology practice. Therefore, the scientific community will benefit from the largest comprehensive database of human fully annotated FFPE biospecimens already available at their disposal in order to demystify the complexity and the heterogeneity of many challenging diseases and foster the transition towards precision medicine.