False positive somatic calls could arise from sequencing and mapping errors. More false positives tend to be called in the non-coding regions of the genome because these regions are enriched for repeats and low sequence complexity regions. As the downstream mutation recurrence analysis is extremely sensitive to recurrent artefacts in somatic mutation calling, we applied additional post-processing filters to eliminate potential false positive calls. We removed candidate somatic mutation calls that:Are found at >1% allele frequency in the 1000 Genomes Project69 (potential germline mutations)Are found in more than 10% of the matched normal samples (potential systematic sequencing errors)Are found in more than 1% of the matched normal samples and are within 20 bp to a common indel in the 1000 Genomes Project (potential errors arising from mapping errors near indels).