I don't think that evolve is the right word here. It is not that cancers generally will develop to the point where this is no longer useful in humans. In a single human it is possible that some collection of cancer cells mutates in a way that makes them resistant or immune from this effect (e.g.: by not having the mutated PCNA), and so that strain will become the dominant cancer in that one person. It is also possible that this pathway is pretty common, and this drug does not help out much because of that. But because cancer is not spread (outside of some rare cases), this is not really going to "evolve" like viruses do.