Evaluating the restoration of DNA derived from archival formalin-fixed paraffin embedded tissues for genomic profiling by SNP-CGH analysis

Pathology archives contain vast resources of clinical material in the form of formalin-fixed paraffin embedded (FFPE) tissue samples. Due to the methods of tissue fixation and storage, the integrity of DNA and RNA available from FFPE tissue is compromised, meaning obtaining informative data regarding epigenetic, genomic and expression alterations can be challenging. Here we have investigated the utility of repairing damaged DNA derived from FFPE tumours prior to single nucleotide polymorphism (SNP) arrays for whole genome DNA copy number analysis. To investigate whether repairing the DNA might improve performance in SNP array assay, we used the DNA Restore protocol from Illumina as a pre-treatment step prior to applying the DNA to the Infinium assay using the Human CytoSNP FFPE-12v2.1 arrays. DNA was extracted from FFPE samples spanning five decades involving tumor material obtained from surgical specimens and post-mortems. Various aspects of the protocol were assessed, including the method of DNA extraction, the role of Quality Control quantitative PCR in predicting sample success and the effect of DNA restoration on assay performance, data quality and the prediction of copy number aberrations (CNAs). In total 8 cases were analysed in this experiment, involving 43 SNP arrays of tumour and matched normal DNA samples, replicates and other control arrays.