Different pathways of colorectal carcinogenesis and their clinical pictures.

An entertaining debate in cancer genetics concerns the relative importance of selection for a growth advantage and genomic instability in tumorigenesis. Below, I present evidence that shows that selection is more important, particularly in the early stages of tumorigenesis, but that genomic instability is also an indisputable feature of many cancers. One attractive possibility is that some mutations may have pleiotropic effects both on cell replication or apoptosis and on genomic instability.