Attacking cancer with chemotherapy or radiation will kill a great number of the fast-growing cancer cells, but not all. There will always be a certain percentage that will survive. Focusing only on the immediate gratification of tumor shrinkage can leave you handicapped in fighting the long-term battle. The strategy cannot just focus on the cancer, it needs to take into account the individual in which it develops.
Cancer is a multifactorial, complex, intelligent, and adaptive disease.