Chemotherapy
Chemotherapy (chemo) is one of the most common treatments for cancer. Learning about how it works and what to expect can help you prepare for treatment and make informed decisions about your care.
What is chemotherapy?
Chemotherapy is a treatment that uses medicines to destroy cancer cells. There are many different types of chemo. They don’t all work exactly the same way, so different types of chemo might be used for different types of cancer. Most are given as an infusion into a vein (IV), but some are given as an injection, taken as pills, or applied to the skin.
What is the goal of chemo?
If your doctor has recommended chemo, it’s important to understand the goal of treatment. This can depend on your type of cancer, its stage (size and location), and how far it has spread. Chemo can have 3 possible treatment goals:
Whenever possible, the goal of chemo is to cure the cancer – destroying it completely so it doesn’t come back. Doctors may call this “treatment with curative intent.” They may avoid saying “cure” because it can take many years to know for sure if the cancer is truly gone. Cure is the hope, but it’s not always possible.
If a cure is not possible, chemo may be used to slow the cancer down or shrink it. This can help people feel better and live longer. The cancer might not go away completely, but it can often be controlled and managed as a chronic disease like heart disease or diabetes. Sometimes the cancer may go away for a while but come back later.
Chemo might be given to improve comfort and quality of life, even when the cancer has spread or can’t be controlled. For example, it may help shrink a tumor that’s causing pressure or pain. This is called palliative chemo.
Palliative chemo is just one part of palliative care, which includes things like pain relief and anti-nausea medicine. Palliative treatments can be used at any stage of cancer.
How is chemo different from other cancer treatments?
Chemo is a systemic treatment. It travels through the bloodstream to reach all parts of your body. It can kill cancer cells that have spread (metastasized) to parts of the body far away from the original (primary) tumor or cancer cells in blood cancers, such as leukemia, that have spread throughout the body. This makes chemo different from local treatments like surgery and radiation, which only affect one part of the body.
How chemotherapy works
Understanding how chemotherapy works can help you know what to expect during treatment.
Chemotherapy interrupts the cell cycle
Chemotherapy works by affecting cells when they are growing and dividing to make new cells. During this process (called the cell cycle), cells:
- Grow in size
- Make copies of their genetic material (DNA)
- Divide to form new cells
Some cells, such as skin cells, are fast growing, meaning they move through this process quickly. Other cells, such as muscle cells, complete it more slowly. Cancer cells tend to be faster growing, moving through the cell cycle very quickly.
Different types of chemo target cells at different phases of the cell cycle. This is why certain chemo drugs work better for different types of cancer cells, and sometimes different combinations of chemo work better together. Understanding how chemo works also helps doctors plan how often each chemo should be given, and how those doses should be timed.
Chemo affects normal cells, too
Chemo interrupts the cell cycles of normal cells, too – especially cells that grow faster, like hair or skin cells. This is why chemo often causes certain side effects, like hair loss.
The good news is that most normal cells will recover from chemo. Chemo is a useful cancer treatment because cancer cells are abnormal (mutated) and less able to recover from its effects.
To work best, chemo treatments must be at just the right dose to kill the cancer cells while sparing as many normal cells as possible.
Are all medicines used to treat cancer called chemo?
Not all cancer medicines are chemotherapy. Other medicines and biological treatments may be used alone or with chemo or other treatments. They work differently and often have different side effects.
- Targeted therapy: These find and attack specific proteins or receptors that some cancer cells have, without affecting most normal cells.
- Hormone therapy: These block or lower hormones that help some cancers (like breast, prostate, and endometrial (uterine) cancers) grow. They either stop the body from making the hormone or block the cancer cells from using it.
- Immunotherapy: These help a person's immune system recognize and attack certain types of cancer cells.
Although these treatments can be very effective, they are more specialized than traditional chemo. They might only work on certain types of cancer, often based on specific traits of the cancer cells. And because many of them are newer, less is known about their long-term side effects. Sometimes they are used only when chemo isn’t working or is no longer effective.
What is it like to get chemo?
Most people get chemo as infusions at a clinic or hospital. But some types of chemo can be taken by mouth or applied to the skin at home. Each type has its own routine, side effects, and safety steps. Learn what it’s like to get each type of chemo and how to stay safe during treatment.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
American Society of Clinical Oncology. What is Chemotherapy? Accessed at cancer.net. Content is no longer available.
Anderson MK, Dickman E, Schmitt ML. Overview of cancer and cancer treatment. In Olsen MM, LeFebvre KB, Walker SL, Dunphy EP, eds. Chemotherapy and Immunotherapy Guidelines and Recommendations for Practice. 2nd ed. Pittsburgh, PA: Oncology Nursing Society; 2023:29-52.
Gilson S. Chemotherapy. In Maloney-Newton S, Hickey M, Brant JM, eds. Mosby’s Oncology Nursing Advisor: A Comprehensive Guide to Clinical Practice. 3rd ed. St. Louis: Elsevier; 2024:388-408.
National Cancer Institute (NCI). Chemotherapy to treat cancer. Updated August 23, 2022. Accessed from https://www.cancer.gov/about-cancer/treatment/types/chemotherapy on April 3, 2025.
Olsen MM, Fritzsche D, O’Connor SL. Chemotherapy. In Olsen MM, LeFebvre KB, Walker SL, Dunphy EP, eds. Chemotherapy and Immunotherapy Guidelines and Recommendations for Practice. 2nd ed. Pittsburgh, PA: Oncology Nursing Society; 2023:67-100.
Last Revised: May 15, 2025
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