Its main functions are:

- To slow cell growth down in order to control and diminish the secondary effects of the disease.

- To avoid the propagation of the cancer cells (the ability to metastasise).

- To kill malignant cells and achieve a cure.

Although chemotherapy treatment protocols vary for each condition, one or more drugs are normally administered in cycles. That is to say, the patient receives, for example, chemotherapy on one or more days (consecutive or with a gap in between) every three or four weeks, so that the body has time to recover its healthy cells and be better able to tolerate the treatment.

Depending on the type of chemotherapy in question, it can be administered at home, or on an out-patient basis, although in some cases it is necessary for the patient to be admitted to hospital.

It can be administered in different ways:

- Oral: in the form of a tablet, capsule or solution.

- Topical: in the form of creams or lotions.

- Intrathecal: to reach the cells present in the central nervous system the drugs are applied directly to the cerebrospinal fluid by means of a lumbar puncture (the lower part of the vertebral column).

- Subcutaneous: as an injection.

- Intravenous: for those patients for whom it is necessary to administer the drugs repeatedly, it is sometimes necessary to install a catheter in one of the large veins in the arm, thorax or neck.

Since these drugs do not act selectively only on cancer cells, they also affect the body's rapidly reproducing healthy cells. This partly explains chemotherapy's side effects, which can vary from patient to patient, and which are usually resolved once the treatment comes to an end. It is important to ask the doctors about the specific side effects of the drugs the patient will receive.

Some of the most frequent side effects are as follows:

- Nausea and vomiting: this tends to happen during the administration of the drugs and can last until a few days after treatment stops. The medicines used to prevent this are quite effective.

- Hair loss: it is common for this to affect the whole body. When treatment stops, hair may grow back with a different colour, shape and texture to what it had before.

- Alteration in the blood count: the number of cells in the blood tends to decrease. A drop in the number of red blood cells will lead to symptoms of anemia, a decrease in the number of white blood cells will make the patient susceptible to infections, and a decrease in the number of platelets can lead to spontaneous bleeding. For this reason it is necessary, in some cases, to perform a blood and platelet transfusion, as well as to administer antibiotics.

- Mucositis: chemotherapy produces desquamation of the cells lining the entire gastrointestinal tract and may cause mouth ulcers and diarrhoea. It is therefore essential to take delicate care of the gums and teeth and to stay well hydrated.

- Fertility and sex life: sexual desire normally decreases during treatment. It tends to affect the menstrual cycle in women, causing irregular periods, which may even disappear. It can also cause symptoms associated with menopause such as hot flushes and vaginal dryness. In some cases it is possible to freeze fertilised eggs and ovarian tissue with a view to possible future pregnancy. In men, sperm production can be affected and the recommendation is to have it frozen before treatment starts. It is advisable to use contraception during treatment, because chemotherapy can cause congenital defects.

- Changes in mood: chemotherapy changes the course of daily life and in some cases patients present alterations to their emotional state, such as experiencing sadness or fear. It is important for patients to tell their doctors about this so that the necessary assistance can be given, both to the patient, and their carers.

During treatment, it is very important for patients to follow a healthy lifestyle, rest sufficiently, eat well, and follow the recommendations of their doctors. Before starting any other medication or taking any food supplements, patients should ask their doctors whether this could interfere with their treatment.