Chemotherapy

I

Introduction

Chemotherapy, treatment of an illness or other medical condition using drugs. The term most commonly refers to the treatment of cancer using specific drugs designed to destroy cancer cells, thereby slowing or reversing the growth rate of tumors. The drugs used in chemotherapy attack a specific tumor, but they also travel to the entire body through the bloodstream, destroying cancerous cells that have spread and which might otherwise form new tumors.

Chemotherapy is just one of the weapons used to treat cancer. Depending on the type of cancerous growth and its location in the body, oncologists (physicians who specialize in cancer treatment) can also use surgery to remove tumors. Another treatment is radiation, using concentrated X rays or other energy particles to destroy cancer cells (see Radiology). Unlike chemotherapy, however, surgery and radiation are local treatments only, useful for attacking a specific tumor and any cancerous threat in immediately surrounding tissue.

Many of the chemotherapeutic drugs used today are cytotoxic (cell-killing) for both malignant and normal cells. As normal cells die off, unpleasant side effects commonly result. But current biomedical research is making considerable strides in designing and introducing new drugs that specifically attack cancer cells while not affecting healthy cells. Such drugs have already begun to transform cancer treatment. Chemotherapy has achieved marked success in curing some forms of cancer, including Hodgkin’s disease, non-Hodgkin’s lymphoma, some forms of leukemia, and testicular cancer. It has also, alone or in combination with other forms of therapy, achieved significant results against cancers of the breast, ovary, and bladder.

II

How Chemotherapy Works

At any given moment in the human body, billions of healthy cells undergo a balanced, orderly cycle of renewal and replacement. Old cells die and new ones—created through the process of cell division—take their place. In cancerous cells, however, the mechanisms regulating cell division break down, and cells divide rapidly without control, ultimately massing into tumors.

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Chemotherapy drugs work by interfering with this cell cycle. Some drugs affect specific phases of the cell cycle, such as the replication of deoxyribonucleic acid (DNA), the coiled molecule that contains the cell’s hereditary instructions. Other drugs attack cancerous cells at any part of the cell cycle. Chemotherapeutic drugs have the greatest effect on cells that undergo rapid division. While this means that the drugs effectively kill cancerous cells, they also attack healthy cells that tend to divide rapidly, such as those found in hair follicles, the mouth, the digestive system, and bone marrow.

As these healthy cells die, unpleasant side effects develop. One common side effect is hair loss. Sores of the mouth are another frequent side effect. Nausea and vomiting are also common, due to the drugs’ effect on the cells of the stomach and other organs of the digestive system. Antinausea and antianxiety drugs can help with these symptoms. If chemotherapy affects the bone marrow, the production of infection-fighting white blood cells of the immune system is reduced or halted. Physicians must carefully monitor a chemotherapy patient’s white-cell count and be prepared to treat opportunistic infections, usually harmless infections that can overwhelm the body and cause disease in those with damaged immune systems.

III

Types of Chemotherapy

There are several types of chemotherapeutic drugs available for the treatment of malignancies. Alkylating agents, for example, are effective in all phases of the cell cycle. These drugs bind to DNA inside the cell and prevent the cell from dividing. Alkylating agents are used to treat cancers of the lymph system (such as Hodgkin’s disease), certain forms of leukemia, and other malignancies.

Drugs in the class known as nitrosoureas interfere with DNA repair. They are primarily used in treating brain cancer. Another group of chemotherapy drugs, referred to as antimetabolites, interfere with cell replication by preventing the cell from assembling the building blocks of DNA and ribonucleic acid (RNA), the molecule that directs protein synthesis. Antimetabolites are used to treat breast cancer, ovarian cancer, and cancers of the gastrointestinal tract.

Mitotic inhibitors constitute another class of chemotherapeutic agents. As their name implies, these drugs interfere with mitosis, the part of the cell cycle when the cell actually divides. These agents are used to treat lung cancer, breast cancer, and testicular cancer. Another class of cancer drugs, known as antitumor antibiotics, treat a variety of cancers, including leukemias. These drugs work by inhibiting the synthesis of RNA.

Still another class of drugs works by raising or lowering the body’s production and processing of sex hormones. These naturally occurring substances can increase or inhibit the growth of tumors. For instance, some breast and ovarian cancers in females need estrogen to grow, while prostate cancer in males needs testosterone to grow. Some chemotherapeutic compounds, therefore, are designed to interfere with these hormones. The drug tamoxifen, for example, blocks the action of estrogen in females and is used to treat breast cancer.

IV

How Chemotherapy Is Administered

A cancer patient often receives two or more chemotherapy drugs at the same time. Such combination therapy provides a maximum assault on cancer cells, since each drug attacks different parts of the cell cycle. This approach enables physicians to prescribe lower dosages of each drug than would be needed if one drug was used alone, lessening the toxic side effects of chemotherapy. Combination therapy can also prevent cancer cells from developing resistance to chemotherapeutic agents, as might occur after prolonged exposure to a single drug.

Chemotherapy is also frequently combined with surgery and radiation to fight cancer. In some instances, chemotherapy can render cancer cells more prone to the effects of radiation. Chemotherapy can also enhance the effects of surgery, since the drugs can reach and destroy cancerous cells near the site of a surgically removed tumor. Ideally, the combination of surgery, radiation, and chemotherapy will attack and neutralize cancer while maintaining as much of the body’s healthy cells and tissue as possible.

Depending on the drug and the type of cancer, chemotherapy can be administered in pill form or by a needle injected into a muscle, under the skin, or into a vein (known as an intravenous injection). In the case of an intravenous injection, the drug may be injected into the body all at once or allowed to drip slowly into the body from a bag suspended above the patient.

To save a patient from repeated sticks of a needle each time an intravenous drug is given, doctors sometimes install vascular access devices. One such device consists of a flexible tube called a catheter. One end of the catheter is inserted under the skin and the other end is attached to a port, an opening through which medicine is inserted. The catheter permits not only the administration of drugs but also the drawing of blood. Ports can also be surgically inserted beneath the skin, often near the collarbone. Some patients use miniature pumps containing chemotherapy drugs. These pumps are small enough to fit unobtrusively in a pocket or on a belt, enabling patients to leave a treatment facility and go about their normal routines while the pump automatically feeds a steady dosage of drugs through a port.

Chemotherapy is usually administered in cycles, in which treatment periods alternate with periods when the body is given the chance to rest and recover. Chemotherapy schedules vary widely, depending on the patient’s illness. One patient may receive medication one day a month, another patient five times a week, and another in three-week intervals. An entire course of chemotherapy treatment can last from a matter of weeks to several months or longer.

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