Cancer is uncontrolled harmful growth of our own cells. It always happens in all of us, but normal healthy systems clean it out. If enough damage is sustained by our systems, such as from radiation, malnourishment, toxins and/or parasites, we are no longer able to maintain ourselves.

Thus there are many kinds of cancer, and unless the sources of the damage to our immune systems are resolved, it will absolutely return. Radiative and chemical attacks upon us, such as "chemotherapy" will cause lasting damage and make the body more susceptible to all sorts of problems, including harder cancer.