Oncology is the study of tumour or cancer. Most of the tumours are not cancerous. The cancerous tumours are called malignant tumours. Commonly oncology implies the study of malignant tumours or cancer. The doctor who practices oncology is an oncologist. There are different kinds of oncologists. Those who practiced in surgery are called surgical oncologists. Those who practiced in radiation therapy are called radiation oncologists. Those who practiced in the care of persons with cancer and administer chemotherapy are medical oncologists.