It takes (usually) four to six oncogene activations to take a cell (or its progeny) into serious, lifethreatening, mofo cancer mode. Things need to be turned of

It takes (usually) four to six oncogene activations to take a cell (or its progeny) into serious, lifethreatening, mofo cancer mode. Things need to be turned off - programmed cell death (apoptosis), DNA repair, sensitivity to growth-suppressing signals from neighbours, etc - and turned on - ability to 'eat' through neighbouring tissues so it can metastasize via your bloodstream, ability to send out vascularisation signals so that the growing tumour can co-opt the body to send some capillaries and minor veins its way before it starves and chokes from being too big - and so on. Apoptosis (suicide) of a cell before it gets more/all of these (assuming they're irreperable, which is the first resort, of course) is a fantastic safety mechanism. Override it at your peril.