Reconstruction of clonal trees and tumor composition from multi-sample sequencing data.
Bottom Line: We derive a combinatorial characterization of the solutions to this problem and show that the problem is NP-complete.We derive an integer linear programming solution to the VAF factorization problem in the case of error-free data and extend this solution to real data with a probabilistic model for errors.The resulting AncesTree algorithm is better able to identify ancestral relationships between individual mutations than existing approaches, particularly in ultra-deep sequencing data when high read counts for mutations yield high confidence VAFs.
Affiliation: Center for Computational Molecular Biology and Department of Computer Science, Brown University, Providence, RI 02912, USA.Show MeSH
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Mentions: Figure 5A shows the clonal tree inferred by AncesTree for CLL patient 077 previously analyzed with both PhyloSub and CITUP. The structure of our clonal tree closely resembles the trees reported by the other algorithms (Fig. 5C); in particular, both trees have two branching lineages containing mutations in the same genes. Furthermore, AncesTree returns purity estimates within 0.04 and 0.05, respectively, of those reported by PhyloSub and CITUP across all five tumor samples. However, there are also important differences between the trees. PhyloSub and CITUP group together multiple pairs of mutations that AncesTree separates into successive clones. For instance, PhyloSub and CITUP cluster MAP2K1, HMCN1 and NOD1 into a single clone, whereas the tree produced by AncesTree shows these mutations as the result of three successive clonal expansions. The extremely high read counts (>450 K) for these three mutations across all five samples give high confidence in the posterior probability of the ancestral relationships: the minimum posterior probabilities over all samples are 0.86 and 1 for the two edges. Similarly, PLA2G16 EXOC6B as is reported in AncesTree’s clonal tree (Fig. 5B).Fig. 5.
Affiliation: Center for Computational Molecular Biology and Department of Computer Science, Brown University, Providence, RI 02912, USA.