Genes do not cause neither disease nor cancer.
They indicate a predisposition to disease.
Gene mutation is a creative response to a perturbation. Not an error.
    Living entities are controlled by  two conservation  laws:
1. Conservation of the individual
    A living system  responds to an external
    perturbation by restructuring its processes so as to
    improve its survival
2. Conservation of the community
    Reproduce by all means