Colorectal cancer: how does it start? How does it metastasize?

Colorectal carcinogenesis is a multistep process with an apparently orderly progression from benign tissue to invasive malignancy and metastases. Yet at the genome level, a considerably more chaotic situation exists, with order arising through the process of natural selection in the midst of genomic instability. Major pathways for colorectal carcinogenesis begin with suppressor loss or acquisition of a mutator phenotype, but there are other pathways known and yet to be described. These pathways result in the natural selection of cells with unstable genomes leading to malignancy and metastases.