Oncology is a branch of medicine that deals with the study, treatment, diagnosis, and prevention of cancer. A medical professional who practices oncology is called an oncologist. The name "oncology" comes from the Greek word "onkos," which means "tumor," "volume," or "mass". Oncology is concerned with the diagnosis of any cancer in a person, including its type and stage. There are several sub-specialties in oncology, including:

• Medical oncology: focuses on treating cancer with chemotherapy, targeted therapy, immunotherapy, and hormonal therapy.
• Surgical oncology: focuses on treating cancer with surgery, including removing the tumor and nearby tissue during an operation.
• Radiation oncology: focuses on treating cancer with radiation therapy, which is the use of high-energy x-rays or other particles to destroy cancer cells.
• Clinical oncology: focuses on treating cancer with both systemic therapies and radiation.
• Sub-specialties in Oncology: include neuro-oncology, ocular oncology, dermatological oncology, genitourinary oncology, gynecologic oncology, pediatric oncology, adolescent and young adult (AYA) oncology, and hemato oncology.

Oncologists manage a patients care throughout the course of the disease, starting with the diagnosis. Their role includes recommending tests to determine whether a person has cancer, explaining a cancer diagnosis, talking about all treatment options and the patients treatment choice, delivering quality and compassionate care, and helping the patient manage symptoms and side effects of cancer and its treatment. A persons cancer treatment plan may include more than one type of oncology treatment. If a person is diagnosed with cancer or is suspected to have cancer, a general practitioner may provide a referral to an oncologist.