Due to uncertainty in tumor phylogeny inference from sequencing data, many methods infer multiple, equally plausible phylogenies for the same cancer. To summarize the solution space
of tumor phylogenies, consensus tree methods seek a single best representative tree
S
under a specified pairwise tree distance function. One such distance function is the ancestor–descendant (AD) distance
, which equals the size of the symmetric difference of the transitive closures of the edge sets
and
. Here, we show that finding a consensus tree
S
for tumor phylogenies
that minimizes the total AD distance
is NP-hard.