Oncology is the study of cancer. An oncologist is a doctor who treats cancer and provides medical care for a person diagnosed with cancer. The field of oncology has three major areas: medical, surgical, and radiation. A medical oncologist treats cancer using chemotherapy or other medications, such as targeted therapy or immunotherapy. A surgical oncologist removes the tumor and nearby tissue during surgery. He or she also performs certain types of biopsies to help diagnose cancer. A radiation oncologist treats cancer using radiation therapy. Other types of oncologists include:A gynecologic oncologist treats gynecologic cancers, such as uterine, ovarian, and cervical cancers. A pediatric oncologist treats cancer in children. Some types of cancer occur most often in children and teenagers. This includes certain brain tumors, leukemia, osteosarcoma, and Ewing’s sarcoma. Types of cancer more common in children sometimes also occur in adults. In these situations, an adult may decide to work with a pediatric oncologist. A hematologist-oncologist diagnoses and treats blood cancers, such as leukemia, lymphoma, and myeloma.