How Chemotherapy Drugs Work

Medically Reviewed By William C. Lloyd III, MD, FACS
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senior Caucasian male receiving chemotherapy in hospital speaking with doctor

You probably know that chemotherapy is often used to treat cancer, but do you know how chemotherapy works? Understanding how chemo drugs work can help you understand how and why chemotherapy causes side effects, such as nausea and hair loss.

How Chemotherapy Treats Cancer

Chemotherapy kills cancer cells because it interrupts their abnormal growth cycle.

Cancer cells grow and divide very quickly. Chemo drugs target rapidly dividing cells and can stop or slow the spread of cancer. The hope is that the drugs destroy cancer cells more quickly than the cells can reproduce.

Doctors can use chemotherapy to cure cancer or put it into remission. Sometimes, doctors treat patients with chemotherapy before surgery because the chemo may shrink the tumor and make it easier to remove. Healthcare providers can also use chemotherapy to ease cancer-related symptoms. Chemotherapy treatment may be worthwhile even if a cure is unlikely, as chemo may shrink tumors that are causing pain and other uncomfortable symptoms.

Chemotherapy vs. Radiation

Chemotherapy and radiation both kill cancer cells, but they do so in a different manner. Chemotherapy drugs interfere with the biological processes that allow cells to divide and reproduce. Radiation damages the DNA, or deoxyribonucleic acid (the genetic material) inside cells. There is enough damage that the cells can longer divide. They die over the course of treatment and even after radiation therapy ends. Radiation also damages the microcirculation that provides nourishment and oxygen to tumors.

One big difference between chemotherapy and radiation is that chemotherapy works throughout the body; radiation is directed toward a specific area. Because chemotherapy travels through the body, it can prevent the spread of cancer and treat tumors in different areas. Radiation is targeted at a focused area and only works there. A person who has breast cancer, for instance, may receive radiation to the chest, directed very specifically at the area of the tumor.

Because chemotherapy affects the whole body, it can cause side effects in many parts of the body, especially to healthy cells that are constantly dividing, such as cells in the skin or mucosal surfaces. In contrast, radiation-related side effects are typically confined to the area targeted by the radiation. A woman undergoing treatment for breast cancer might develop skin irritation or radiation burns on her chest; her lungs may also experience radiation-related side effects.

Some patients receive both chemotherapy and radiation therapy.

Chemotherapy Side Effects

Chemotherapy drugs can effectively kill cancer because they kill or slow the growth of quickly dividing cells. They do not exclusively target cancer cells; all quickly dividing cells in the body can be affected, including the hair cells, intestinal cells, and the cells that line the inside of the mouth.

Many of chemotherapy’s side effects are the result of damage to fast-growing cells. Nausea and vomiting are caused by damage to the lining of the digestive tract. Hair loss occurs because chemotherapy attacks the rapidly growing cells in hair roots. Mouth sores result when chemo affects the cells inside the mouth.

Chemotherapy and blood health

The bone marrow is another part of the body that is constantly producing new cells. Bone marrow makes red blood cells (which carry oxygen throughout the body), white blood cells (which help fight infection), and platelets (which aid blood clotting).

Because chemotherapy attacks different rapidly-proliferating cell lines, the bone marrow’s ability to produce new red and white blood cells and platelets is decreased during chemo treatment. As a result, people are vulnerable to infection (due to a lower-than-usual number of white blood cells) and fatigue (due to a lack of oxygen-carrying red blood cells) while undergoing chemotherapy.

Most side effects of chemotherapy go away when treatment is over. There are many different types of chemotherapy drugs, and some have more severe side effects than others. If you have specific questions about your chemotherapy or its side effects, talk with your oncologist.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Feb 9
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