Chemotherapy and radiation can weaken the immune system

How Does Cancer Treatment Affect the Immune System? Chemotherapy (chemo) and radiation therapy (also called radiotherapy) kill cancer cells. The problem is, they also kill rapidly dividing healthy cells. Each treatment has its own effects. When the two treatments are combined, which is common, you can end up with side effects of both.

Chemotherapy. Chemotherapy is a systemic treatment, meaning it affects your whole body. Many types of chemo are given as injections or infusions. It can also be given by mouth, in pill form. Cancer cells grow and divide quickly. Chemo is designed to go after fast-growing cells like cancer. However, it can’t tell one fast-growing cell from another. That means it kills many types of cells in your body. That includes bone marrow cells. One of their jobs is to produce white blood cells for the immune system. White blood cells are responsible for attacking and killing viruses, bacteria, and other pathogens. But when chemo kills off bone marrow cells, your immune system doesn’t have enough white blood cells to fight off infections. The most common chemo-related problem is neutropenia. This is a decrease in neutrophils (white blood cells), which are important for immunity.

Radiation. Radiation works differently than chemo. It exposes your cells to high doses of radiation (high-energy beams) that damage their DNA (genetic material). This means cells either die or become unable to divide, which is how cells reproduce. This shrinks tumors or slows their growth. As with chemo, healthy cells are damaged by radiation, too.1 But radiation may have less of a damaging effect on the immune system in general. That’s because radiation isn’t systemic. Rather, it is targeted right at your tumor. Oftentimes, however, radiation does have to travel through areas of healthy cells to get to the tumor, so either those cells or cells nearby the tumor can be affected.

Depending on where the tumor being treated is located in the body, radiation may directly damage your immune system. It may also cause other conditions that harm the immune system. For example, radiation near the underarm can damage lymph nodes, which are part of the immune system. The damage can lead to an increased risk of infection in the arm. Radiation can deal a lot of damage when it’s aimed at bones. The effect on bone marrow is similar to that of chemo. Neutropenia is common.

How Strong Is Your Immune System After Cancer Treatment? After chemo and radiation, your immune system can stay suppressed for several months. A study of people who had chemo for breast cancer found the immune system often took nine months or more to fully recover. Several types of immune-system cells were depleted. In people who smoked, some immune cells were only at 50% of normal levels after nine months. That’s compared to an 80% rate in nonsmokers. Researchers say the immune-system damage could leave you vulnerable to some illnesses even if you’ve been vaccinated. These include tetanus (a bacterial infection) and pneumonia (inflection causing inflammation of the air sacs of the lungs).

Specific chemo drugs have different effects. In the study, people given the drug anthracycline (a type of chemotherapy that is an antibiotic) had normal immune function by the end of the study period. Those who took anthracycline plus taxane, a more traditional chemo drug, recovered much more slowly. While newer research has been illuminating, much remains to be learned about the specific immune-system effects of cancer treatments.

Chemotherapy kills fast-growing cells, which includes many healthy cells, along with cancer cells. Bone marrow cells are frequently damaged and unable to produce white blood cells. This hampers your immune system. Radiation damages the genetic material of cells. This kills both cancer and immune-system cells. Effects tend to be less than with chemo. Radiation may directly damage the immune system or may cause other conditions that impair your immunity. Much of this depends on where the cancer is. Your immune system may take months to rebound after chemo and radiation. Be sure to take steps to protect yourself from infection. If you notice symptoms of infection, get medical attention right away.

More people are surviving and thriving after cancer all the time. Once you beat the disease, though, you can’t let up your guard. Impaired immunity can pose a real threat. Just being aware of the problem is a start. Adopting good habits, enlisting friends and family to help, and staying in touch with your care team can help you stay healthy until your immune system is strong enough to protect you again.