Cancer (Chemotherapy)
Chemotherapy
Chemotherapy is the use of chemical substances to treat disease. In its modern-day use, it refers primarily to cytotoxic drugs used to treat cancer.
Chemotherapy is a treatment used for some types of cancer, leukaemia and lymphoma.
Sometimes Chemotherapy is used to treat non-cancerous conditions but often the doses are lower and the side effects may be reduced. This section does not cover the use of Chemotherapy for conditions other than cancer.
The section is divided into sections about how the treatment works, how it is given and how to deal with some of the more common side effects.
There are over 50 different Chemotherapy drugs. Some are given on their own but often several drugs may be combined (this is known as combination Chemotherapy).
The type of Chemotherapy treatment you are given for your cancer depends on many things, particularly the type of cancer you have, where in the body it started, what the cancer cells look like under the microscope and whether they have spread to other parts of the body.
Principles
Cancer is the uncontrolled growth of cells coupled with maglignant behavior: invasion and metastasis. Cancer is thought to be caused by the interaction between genetic susceptibility and environmental toxins. Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body - in other words, the body attacks its own cells. In contrast, transplant rejection happens because a normal healthy human immune system can distinguish foreign tissues and attempts to destroy them. Also the reverse situation, called graft-versus-host-disease, may take place.
Broadly, most chemotherapeutic drugs work by impairing mitosis (cell division), effectively targeting fast-dividing cells. As these drugs cause damage to cells they are termed cytotoxic. Some drugs cause cells to undergo apoptosis (so-called "programmed cell death").
Unfortunately, scientists have yet to identify specific features of malignant and immune cells that would make them uniquely targetable (barring some recent examples, such as the Philadelphia chromosome as targeted by imatinib). This means that other fast dividing cells such as those responsible for hair growth and for replacement of the intestinal epithelium (lining) are also often affected. However, some drugs have a better side-effect profile than others, enabling doctors to adjust treatment regimens to the advantage of patients in certain situations.
As Chemotherapy affects cell division, tumours with high growth fractions are more sensitive to Chemotherapy, as a larger proportion of the targeted cells are undergoing cell divisionat any time. Malignancies with slower growth rates, such as indolent lymphomas, tend to respond to Chemotherapy much more modestly.
Drugs affect "younger" tumors (i.e. more differentiated) more effectively, because mechanisms regulating cell growth are usually still preserved. With succeeding generations of tumour cells, differentiation is typically lost, growth becomes less regulated, and tumours become less responsive to most chemotherapeutic agents. Near the center of some solid tumours, cell division has effectively ceased, making them insensitive to Chemotherapy
Over time, cancer cells become more resistant to Chemotherapy treatments. Recently, scientists have identified small pumps on the surface of cancer cells that actively move Chemotherapy from inside the cell to the outside.
How Chemotherapy drugs work
Chemotherapy drugs can stop cancer cells dividing and reproducing themselves. As the drugs are carried in the blood, they can reach cancer cells anywhere in the body but are also taken up by healthy cells. Healthy cells can repair the damage caused by Chemotherapy but cancer cells cannot and so they eventually die.
Different Chemotherapy drugs damage cancer cells in different ways. If a combination of drugs is used, each drug is chosen because of its different effects. Unfortunately, as the Chemotherapy drugs can also affect some of the healthy cells in your body, they can cause unpleasant side effects. However, damage to the healthy cells is usually temporary and most side effects will disappear once the treatment is over.
Normal cells grow and die in a controlled way. When cancer occurs, cells in the body that are not normal keep dividing and forming more cells without control. Anticancer drugs destroy cancer cells by stopping them from growing or multiplying. Healthy cells can also be harmed, especially those that divide quickly. Harm to healthy cells is what causes side effects. These cells usually repair themselves after Chemotherapy.
Because some drugs work better together than alone, two or more drugs are often given at the same time. This is called combination Chemotherapy.
Other types of drugs may be used to treat your cancer. These may include certain drugs that can block the effect of your body's hormones. Or doctors may use biological therapy, which is treatment with substances that boost the body's own immune system against cancer. Your body usually makes these substances in small amounts to fight cancer and other diseases. These substances can be made in the laboratory and given to patients to destroy cancer cells or change the way the body reacts to a tumor. They may also help the body repair or make new cells destroyed by Chemotherapy.
Healthy cells in certain parts of the body are especially sensitive to Chemotherapy drugs:
- the lining of the mouth
- the bone marrow (which makes blood cells)
- the hair follicles
- and the digestive system.
Chemotherapy is carefully planned and is usually given as a series of sessions of treatment. Each session is followed by a rest period. The session of Chemotherapy and the rest period is known as a cycle of treatment. A series of cycles makes up a course of treatment.
Each session of Chemotherapy destroys more of the cancer cells, but the rest period allows the normal cells and tissues to recover. Depending on the type of cancer and how advanced it is, Chemotherapy can be used for different goals:
- To cure cancer - with some types of cancer, Chemotherapy is likely to destroy all the cancer cells and cure the disease.
- Cancer is considered cured when the patient remains free of evidence of cancer cells.
- To reduce the chance of a cancer coming back - Chemotherapy may be given after surgery or radiotherapy so that if any cancer cells remain, but are too small to see, they can be destroyed by the Chemotherapy. This is done by keeping the cancer from spreading; slowing the cancer's growth; and killing cancer cells that may have spread to other parts of the body from the original tumor.
To shrink a cancer, reduce symptoms and prolong life - if a cure is not possible, Chemotherapy may be given.
Relieving symptoms such as pain can help patients live more comfortably
Chemotherapy may be given in different ways, depending on the type of cancer you have and the Chemotherapy drugs used:- Most often it is given by injection into a vein (intravenously). This is known as intravenous Chemotherapy.
- Some drugs are given as tablets or capsules (orally).
- Some are injected into a muscle (intramuscular injection).
- Others may be injected just under the skin (subcutaneous injection).
Drugs given in the above ways are absorbed into the blood and carried around the body so they can reach all the cancer cells.
- For some types of cancer, Chemotherapy may be injected into the fluid around the spine. This is known as intrathecal Chemotherapy.
- Sometimes the Chemotherapy may be injected into particular body cavities such as the pelvic cavity or bladder: this is known as intracavity Chemotherapy.
Drugs given in this way tend to stay in the area in which they are given and do not affect cells in other parts of the body.
Chemotherapy creams may be used for some cancers of the skin: they only affect the cells in the area of skin to which the cream is applied. Topically applied
Sometimes, two or more types of Chemotherapy may be used together; for example, intravenous and oral Chemotherapy.Which Drugs Are Given?
Some Chemotherapy drugs are used for many different types of cancer, while others might be used for just one or two types of cancer. Your doctor recommends a treatment plan based on:
- What kind of cancer you have.
- What part of the body the cancer is found.
- The effect of cancer on your normal body functions.
- Your general health.
What About Clinical Trials?
Clinical trials, also called cancer treatment studies or research studies, test new treatments in people with cancer. Clinical trials test many types of treatments such as new drugs, new approaches to surgery or radiation therapy, new combinations of treatments, or new methods such as gene therapy. The goal of this research is to find better ways to treat cancer and help cancer patients. There are different types of clinical trials, called Phase I, Phase II, and Phase III trials. Each is one of the final stages of a long and careful cancer research process. If your doctor does not suggest you take part in a clinical trial, you may want to ask about clinical trials as a treatment choice for you.
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