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Oncology is a broad term to describe the treatment of cancer, and is most often used to mean the non-surgical treatment of malignancy. These non surgical treatments include radiotherapy (X-ray treatment), chemotherapy (drug treatment), hormone drugs, targeted drugs, immunotherapy and supportive medications. These cancer treatments can be used individually as sole treatments, follow one another in a series of treatments, or be used together at the same time. They can also be used as the first treatment (called primary or neoadjuvant), after surgery (adjuvant), or when a cancer has relapsed. They can be used with the aim of trying to cure a cancer, or if incurable, controlling the cancer for as long as possible and helping to relieve symptoms caused by the cancer. How they are actually used will depend on the type of tumour, its stage and the patient's medical history and wishes.
An oncologist is someone who specialises in the treatment of cancer. In the UK there are two types of oncologist, clinical oncologists and medical oncologists. A clinical oncologist can prescribe all the treatments described above, including radiotherapy, whereas a medical oncologist cannot prescribe radiotherapy but can use all the other options.