Oncology ♦ What is Oncology? Oncology is a branch of medicine that deals with the diagnosis and treatment of cancer. A person who is involved in the practice of Oncology is called an oncologist. Oncology is formed with the words ONKOS : BULK, MASS : TUMOR, LOGY MEANING : STUDY OF is. There are three main branches of Oncology: 1) Medical oncology: In this, treatment begins with drugs and chemotherapy.