Phylogenetic Analysis

Phylogenetic analysis was performed as previously described³. In brief, using the pigeon-hole principle (if the average cancer cell fraction of two subclones sums to more than 1, the smaller subclone must be nested within the larger) as well as the crossing rule (if the cancer cell fraction of subclone A and subclone B sums to less than 1 and the cancer cell fraction of subclone A exceeds that of subclone B in one region but the inverse is true in another region, subclone A and B must exist on separate branches of the evolutionary tree), the evolutionary relationships between subclones was determined and a phylogenetic tree inferred.