Normally, your cells grow and die in a controlled way. Cancer cells keep forming without control. Chemotherapy is drug therapy that can stop these cells from multiplying. However, it can also harm healthy cells, which causes side effects.

During chemotherapy you may have no side effects or just a few. The kinds of side effects you have depend on the type and dose of chemotherapy you get. Side effects vary, but common ones are nausea, vomiting, tiredness, pain and hair loss. Healthy cells usually recover after chemotherapy, so most side effects gradually go away.

Your course of therapy will depend on the cancer type, the chemotherapy drugs used, the treatment goal and how your body responds. You may get treatment every day, every week or every month. You may have breaks between treatments so that your body has a chance to build new healthy cells. You might take the drugs by mouth, in a shot or intravenously.

Chemotherapy: Drug treatment uses chemicals to kill cancer cells

Chemotherapy — the use of medications to treat cancer — has played a major role in cancer treatment for half a century. Years of testing and research have proved chemotherapy to be an effective cancer treatment. It may be your only treatment, or it may be used in combination with other treatments, such as surgery and radiation therapy.

Chemotherapy works by killing rapidly dividing cells. These cells include cancer cells, which continuously divide to form more cells, and healthy cells that also divide quickly, such as those in your bone marrow, gastrointestinal tract, reproductive system and hair follicles. Healthy cells usually recover shortly after chemotherapy is complete, so for example, your hair starts growing again.

Chemotherapy can serve varying goals

One of chemotherapy's main advantages is that — unlike radiation, which treats only the area of the body exposed to the radiation — chemotherapy treats the entire body. As a result, any cells that may have broken away from the original cancer are treated.

Depending on what type of cancer you have and whether it has spread, your doctor may use chemotherapy to:

• Eliminate all cancer cells in your body, even when cancer is widespread
• Prolong your life by controlling cancer growth and spread
• Relieve symptoms and enhance your quality of life

In some cases, chemotherapy may be the only treatment you need. More often, it's used in conjunction with other treatments, such as surgery, radiation or a bone marrow transplant, to improve results. For example, you may receive:

• Chemotherapy before other treatments (neoadjuvant chemotherapy). The goal of neoadjuvant therapy is to reduce the size of a tumor before surgery or radiation therapy.
• Chemotherapy after other treatments (adjuvant chemotherapy). Given after surgery or radiation, the goal of adjuvant therapy is to eliminate any cancer cells that might linger in your body after earlier treatments.

How your doctor chooses a chemotherapy regimen

Chemotherapy may not be limited to a single drug. Most chemotherapy is given as a combination of drugs that work together to kill cancer cells. Combining drugs that have different actions at the cellular level may help destroy a greater number of cancer cells and might reduce the risk of your cancer developing resistance to one particular drug. Your doctor will recommend drug combinations that have been tested in people with similar conditions and have been shown to have some effect against your particular type of cancer.

What chemicals your doctor recommends is generally based on the type, stage and grade of your cancer, as well as your age, general health and your willingness to tolerate certain temporary side effects.

How chemotherapy is given

You usually receive chemotherapy in cycles, depending on your condition and which drugs are used. Cycles may include taking the drugs daily, weekly or monthly for a few months or several months, with a recovery period after each treatment. Recovery periods allow time for your body to rest and produce new, healthy cells.

Chemotherapy drugs can be taken in a number of forms. Your doctor decides what form or forms to use primarily based on what type of cancer you have and what drug or combination of drugs will best treat your cancer. Examples of different forms of chemotherapy include:

• Intravenous (IV). Chemotherapy is injected into a vein, using a needle inserted through your skin. This allows rapid distribution of the chemotherapy throughout your entire body.
• Oral. You swallow this form of chemotherapy as a pill.
• Topical. This type of drug is applied to your skin to treat localized skin cancers.
• Injection. Using a needle, your doctor injects the drug directly into a muscle, under your skin or into a cancerous area on your skin.

Chemotherapy medications, regardless of how they're given, generally travel in your bloodstream and throughout your entire body. The intravenous route is the most common, allowing chemotherapy drugs to spread quickly through your system. In cases in which your doctor wants to direct chemotherapy to a more confined area — for example, to ensure a tumor is exposed to more of the drug — he or she may insert a tube (catheter) directly into that area or into a blood vessel supplying the tumor.