Frequency of base transition in formalin-fixed paraffin-embedded (FFPE) samples.

<p><b>A</b>: A strategy for estimation of rates of sequencing errors/background DNA damage and overall base alteration rates. The discrepant bases at homozygous sites in control samples are likely to be sequencing errors or background DNA mutation. Conversely, discrepant bases at homozygous sites in frozen or FFPE tissue samples could be either sequencing errors/background DNA damage or base alteration caused by preservation methods. <b>B</b>: The rate of base alterations caused by formalin fixation. High frequencies of C>T and G>A were observed in FFPE tissue samples only.