Association of fragmentation of DNA in FFPE samples with low sequencing coverage. Coverage of each sample (number of reads) versus the copies of the FTH1 gene as assessed by a Taqman PCR assay (copies per microlitre). n = 253. There was a positive correlation between the FTH1 result and coverage (Spearman correlation, r = −0.29, p < 0.0001). The 50 samples with the highest C>T/G>A levels in the 1-10% allele frequency range are shown in red.