Oncology is the branch of medicine that specializes in the study, diagnosis, treatment, and prevention of cancer. The term comes from the Greek word 'onkos' meaning bulk or mass, referring to tumors. Oncologists are medical doctors who treat cancer through various methods including chemotherapy, radiation therapy, immunotherapy, and surgery. Ornithology studies birds, mammalogy studies mammals, and pedology studies soil - making 'Cancer' the correct answer among the given options.