According to recently published work in Nature, the Cancer Genome Atlas has revealed that many tumors are heterogeneous. More mutations might mean more drug targets, says Derek Lowe, but that's not necessarily a good thing, he writes at In the Pipeline. "Just doing the math on the possible interactions of several dozen mutations with a list of possible treatment regimes is enough to make you pause." The biggest challenge for drug discovery will be finding out what all these mutations do and how they interact with one another.