What are toxic substances? Asbestos, weed killers, DDT, substances listed in Prop 65 that was enacted in 1976, and many others all have been found to increase the risk of cancer. Frankly, sugar is toxic to the brain, so are many artificial sweeteners.
Prevention? Evaluate your environment for the possible presence of cancer-promoting substances. Be careful about the type of water you drink—get the best source possible. Take antibiotics only when absolutely necessary and as ordered. Then take steps to replace healthy bacteria in your small and large intestines because ONE dose of antibiotics can wipe out all positive bacteria in your large bowel.