Cancer treatment and infection risk

Most cancer treatments used today can increase your risk for infection.

Surgery

Any type of major surgery can suppress the immune system, but the reason for this is not very clear. Researchers have seen decreases in immune function within hours of surgery. Anesthesia (the drugs used to make the patient sleep) may play a role. It may take from 10 days to many months for an immune system to recover completely.

Surgery also breaks the skin and mucous membranes and can expose internal tissues to germs. The wound caused by surgery (the incision) is a common place for infection.

Surgery is often used to diagnose, stage, or treat people with cancer. Because surgery is often used to treat people with cancer, it is important to know that surgery can increase the risk of certain infections.

Things that raise the risk of infection after surgery include:

• How long the person was in the hospital
• The extent of the surgery (how much cutting was done)
• How long the operation lasted
• The amount of bleeding during surgery
• The person’s nutritional status
• Prior cancer treatment, such as chemotherapy or radiation
• Other medical problems, such as diabetes, or heart or lung problems

People with cancer may get antibiotics before and for a short time after having surgery to help protect them from infection.

Chemotherapy

Chemotherapy (often called chemo) is the most common cause of a weakened immune system in people getting cancer treatment. The effects on the immune system depend on many things, including:

• Which chemo drugs are used
• Chemo dose (how much of each drug is given at once
• How often chemo is given
• Prior treatments for cancer
• The person’s age
• The person’s nutritional status
• The type of cancer
• The stage of the cancer (how much cancer there is)

Some drugs affect the bone marrow and immune system more than others. But chemo drugs may have different effects on how well the body makes white blood cells, red blood cells, and platelets. In most cases, white blood cells are the ones most affected by chemo drugs.

The chemo’s effect on your blood cells doesn’t last. After treatment ends, your blood cell counts usually go back to normal over time.

Radiation therapy

The effects of radiation therapy on the cells of the bone marrow can be much like the effects of chemo. Both of these treatments may cause low white blood cell counts (including neutropenia), which increases the risk for infections.

Many things affect the degree of neutropenia from radiation therapy. These include:

• The total radiation dose
• The radiation schedule
• The part of the body being treated with radiation
• How much of the body is treated with radiation

Total body irradiation or TBI (where a person’s entire body is treated with radiation) is the only type of radiation likely to cause very low blood counts. Radiation is most often given to just one area of the body, so the whole immune system is not damaged by it. Still, depending on the dose and the part of the body being treated with radiation, the skin or mucous membranes may be damaged, so you’re less able to keep germs out.

Today, radiation treatments are most often given over many sessions rather than in one large dose. This helps decrease the amount of skin and tissue damage, immune suppression, and the risk of infections.

Biotherapy or immunotherapy

Biotherapy is also known as biologic therapy or immunotherapy. It is given to make your immune system better able to recognize and attack cancer cells. This can be done by helping your own immune system work harder or smarter, or by giving you things like man-made immune system proteins. Immunotherapy is sometimes used by itself to treat cancer, but it is often used along with or after another type of treatment to add to its effects.

These treatments promote immune reactions against cancer cells, but sometimes they change the way the immune system works. Because of this, people who get biologic therapies may be at risk for immune suppression and neutropenia. In fact, some immunotherapy drugs lower the levels of all white blood cells (not just neutrophils).

When the lymphocyte levels become low, the chance of getting certain serious viral and fungal infections become very high. Absolute neutrophil counts may also drop. Most of the time the neutrophil counts return to normal soon after the treatment is stopped, but the lymphocyte counts can stay low for months. (For more information see our document Immunotherapy.)

Hematopoietic stem cell transplant (bone marrow transplant)

Hematopoietic stem cell transplant (HSCT) is the term now used to include bone marrow transplant (BMT), peripheral blood stem cell transplant (PBSCT), and umbilical cord blood stem cell transplant (UCBSCT). These transplants require very high doses of chemo and/or total body irradiation (TBI) to try to kill all the cancer cells in the body.

In the process of killing the cancer cells, the blood-forming stem cells of the patient’s normal bone marrow are also killed. Because of this, stem cells (either from the blood or bone marrow) are removed from the patient and saved before the high-dose chemo is given. Or, they may be taken from a donor or banked umbilical cord blood. Once the cancer cells are killed, the saved or donated stem cells are given to the patient so that blood cells can be made and the immune system rebuilt.

High-dose chemo is sometimes used with TBI for transplants. This causes more severe neutropenia that lasts for a longer time. These treatments, especially when used together, also damage the skin and mucous membranes and make them less able to keep germs out of the body.

For these reasons, very strict precautions are taken to try to protect transplant patients from getting infections and treating them quickly if they do. This usually includes:

• Keeping the transplant patient in a special area of the hospital until WBC counts begin to reach normal (this often takes weeks)
• Limiting their exposure to other people or other sources of germs
• Watching them closely for signs of infection, such as fever

Patients who get stem cells from other people may also need medicine to prevent a serious problem called graft-versus-host disease. These medicines suppress the immune system. For more information on transplants, see our document called Stem Cell Transplant (Peripheral Blood, Bone Marrow, and Cord Blood Transplants).