Oncologists are doctors that deal with the prevention, diagnosis, and treatment of cancer. You will see an oncologist if your usual doctor suspects you have cancer. Your oncologist will order tests, confirm, diagnose, and stage your cancer. They will also develop and oversee your treatment plan. Many other people will be involved in a cancer care team, but an oncologist is the leader of that team. Oncologists have a wide range of specialties, and almost all of them further specialize once they complete their oncology training. Oncologists can specialize in most types of cancer.