Also called “chemo,” it’s a way to treat cancer that uses drugs to kill cancer cells.

It targets cells that grow and divide quickly, as cancer cells do. Unlike radiation or surgery, which target specific areas, chemo can work throughout your body. But it can also affect some fast-growing healthy cells, like those of the skin, hair, intestines, and bone marrow. That’s what causes some of the side effects from the treatment.

It depends on the kind of cancer you have and how far along it is.

Cure: In some cases, the treatment can destroy cancer cells to the point that your doctor can no longer detect them in your body. After that, the best outcome is that they never grow back again, but that doesn’t always happen.
Control: In some cases, it may only be able to keep cancer from spreading to other parts of your body or slow the growth of cancer tumors.
Ease symptoms: In some cases, chemotherapy can’t cure or control the spread of cancer and is simply used to shrink tumors that cause pain or pressure. These tumors often continue to grow back.

Sometimes, it treats cancer by itself, but more often it’s used in combination with:

Surgery: A doctor removes cancerous tumors or tissue, or organs contaminated with cancerous cells.
Radiation therapy: A doctor uses invisible radioactive particles to kill cancer cells. It may be delivered by a special machine that bombards parts of your body from the outside, or by putting radioactive material on, near, and even inside your body.
Biological therapy: Living material in the form of bacteria, vaccines, or antibodies are carefully introduced to kill cancer cells.
 
Chemotherapy may be used to:

Shrink a tumor before radiation therapy or surgery — called neoadjuvant chemotherapy
Destroy any remaining cancer cells after surgery or radiation therapy — called adjuvant chemotherapy
Make other therapies (biological or radiation) more effective
Destroy cancer cells that return or spread to other parts of your body

That depends on:

The type of cancer you have
How far along it is
The goal of treatment: cure, control growth, or ease pain
The type of chemotherapy
The way your body responds to the treatment
You may have chemotherapy in “cycles,” which means a period of treatment and then a period of rest. For example, a 4-week cycle may be 1 week of treatment and then 3 weeks of rest. The rest allows your body to make new healthy cells. Once a cycle has been planned out, it’s better not to skip a treatment, but your doctor may suggest it if side effects are serious. Then your medical team will likely plan a new cycle to help you get back on track.