Oncology is the branch of medicine dealing with tumors (cancer). A medical professional who practices oncology is an oncologist. The term originates from the Greek onkos (ονκος), meaning bulk, mass, or tumor, and the suffix -logy, meaning "study of".

Oncology is concerned with:

• The diagnosis of any cancer in a person
• Therapy (e.g., surgery, chemotherapy, radiotherapy and other modalities)
• Follow-up of cancer patients after successful treatment
• Palliative care of patients with terminal malignancies
• Ethical questions surrounding cancer care
• Screening efforts:
-of populations, or
-of the relatives of patients (in types of cancer that are thought to have a hereditary basis, such as breast cancer) .