They aggressively modify their behavior based on whatever it takes to survive. Surgically, we can excise a tumor, examine the usual course of metastases, and appear to have stopped the disease. An awareness of the biological unknowns is what drives the use of cytotoxins and ionizing radiation as prophylaxis tools pre and post op. Medical care in the US is absolutely the best in the world for many reasons, but primarily because we are a wealthy country. The profit motive drives hospital, physician, drug company, and research, generally weeding out under-performing segments and rewarding success.
Oncologists deal with a very serious set of diseases with relatively high failure rates.
I credit all of them for being good practitioners and generally superb humans, who deal with patients in a compassionate and helpful manner. So does failure. The guidelines for clinical practice have been established over time by professional peer groups, governmental oversight, and torts. Medical ethics are, in fact, increasingly defined by court actions that punish inappropriate conduct - exactly as in every other industry. Annually, Oncologists meet, review and publish new and recommended Standard of Care protocols which are almost universally implemented at the clinical practice level.