Cancer is widespread among eukaryotes, and can be successfully tackled only by understanding its place in the story of life itself – especially the evolution of multi-cellularity. In this seminar I will propose a new theory of cancer, drawing on insights from astrobiology. The central hypothesis is that cancer is an organized pre-programmed process driven by a cassette of highly conserved, deeply-evolved ancient genes – genes that are active in early-stage embryo development, and which become inappropriately re-awakened in the adult form. In effect, cancer tumors are atavisms, recapitulating an ancient life form – “Metazoa 1.0” – dating back to the dawn of multi-cellularity. This hypothesis differs fundamentally from the popular notion that cancers are deregulated rogue cells running amok, and explains cancer’s well-known robustness and resilience. It also offers a well-defined target for therapy.