One of the most effective ways to kill off cancer cells is with toxic chemicals called chemotherapy agents, which are drugs developed to target fast-growing cells. There are many different chemotherapy drugs, and some attack a variety of types of cancer while others focus on particular cancers, such as breast cancer or lung cancer.

Chemotherapy drugs work by targeting all fast-growing cells, so they also affect rapidly dividing cells in other parts of the body, such as the hair, the mouth, and the digestive system, which is what leads to common side effects such as dry mouth and hair loss. Unlike radiation and surgery, which are site-specific, or "local," chemotherapy is considered a "systemic" treatment, since the medications travel throughout the body.

• Chemotherapy drugs. Some chemotherapy drugs, called "nonspecific," are capable of killing cancer cells during any phase of growth; others, called "specific," can kill cancer cells only during a specific phase and not while the cell is resting. Doctors often create a chemotherapy regimen by combining specific and nonspecific chemo agents for maximum effect.

When a patient's doctor chooses a drug, she also makes decisions about dosage level, frequency of dosage, and length of treatment. These decisions can affect how easy or difficult it is for the patient to tolerate his chemo regimen. The more you can find out about exactly which drugs will be used, in what dosages, and for how long, the better prepared you and he will be to cope with the side effects to come. Some chemotherapy drugs are given through an IV while others can be taken orally or by injection.

• Chemotherapy schedules. Nowadays, chemotherapy is most often performed on an outpatient basis, though if your friend or relative has to be hospitalized for surgery, the doctor may start chemo while he's still in the hospital.

Chemotherapy is usually given in cycles, with periods of treatment followed by periods of rest to let his body recover. He might receive three weeks of chemo followed by one week of rest, or one week of chemo followed by three weeks of rest. Either way, a full four weeks makes up one cycle. Sometimes a patient has to meet certain health criteria in order to go through the next round of chemotherapy. For example, the doctor may monitor his blood cell counts, and if his white or red blood cell count drops too low, the doctor may have to postpone the next round of chemo until the count rises again.