Oncology is the study of cancer. An oncology doctor who treats cancer and provides medical care for a person diagnosed with cancer. The three major field of oncology has: medical, surgical, and radiation. The types of cancer are carcinoma, sarcoma, melanoma, lymphoma, and leukemia, Carcinomas. The most commonly diagnosed cancers - originate in the skin, lungs, breasts, pancreas, and other organs and glands.