Mutational spectra and tumor composition. (A) The mutational opportunity spectrum of the human genome across 96 trinucleotide channels and the mutational signatures found in the breast cancer data. For each mutation, the 16 sequence contexts are ordered by the 5' and then the 3' base in the order A, C, G and T, that is, from ApCpA, ApCpC to TpCpG, TpCpT. The error bars were estimated analytically (see Additional file 1). (B) The contributions of each mutational process towards the mutations for each tumor. The correlation with cancer subtype matches that reported in .