Why are most mutations in cancer cells called 'passengers.'?

What allows cancer live at high mutation rate? Which mutations make it weaker? Is there a way to exploit its natural mechanisms to make it less evolvable? Harvard Associate Professor, Leonid Mirny, on clinical phenomena we can now explain using the balance between ‘drivers’ and ‘passengers’.

Cancer is an evolutionary process. There are accumulations of mutations and then there is selection from mutations that make cells more malignant, more like cancer cells. Mutations come at random.