Chemotherapy for Breast Cancer May Increase Risk of Common Infections

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Chemotherapy treatment uses medicine to weaken and destroy cancer cells in the body, including cells at the original cancer site and any cancer cells that may have spread to another part of the body. Chemotherapy is systemic therapy, which means it affects the whole body by going through the bloodstream.

Cancer cells tend to grow and divide very quickly, with no order or control, and chemotherapy destroys these rapidly dividing cells. Most normal cells in your body grow and divide in an orderly way. But some normal cells do divide quickly, including cells in hair follicles, nails, the mouth, digestive tract, and bone marrow. Chemotherapy can affect these cells, too. So this is why most women lose their hair, have mouth sores, or other side effects during chemotherapy.


Your bone marrow makes blood cells, including specialized white blood cells called lymphocytes. Lymphocytes are part of your body’s immune response and help you fight infections.

Because chemotherapy can affect bone marrow, researchers wondered if being treated with chemotherapy for breast cancer could affect how the immune system functions.

A study has found that women diagnosed with breast cancer who were treated with chemotherapy had lower levels of lymphocytes for at least 9 months after chemotherapy ended.

The research was published in the January 2016 issue of Breast Cancer Research. Read “Lymphocyte depletion and repopulation after chemotherapy for primary breast cancer.”

In the study, the researchers measured the lymphocyte levels of 88 women who had been diagnosed with breast cancer before they started chemotherapy and several times after chemotherapy was completed, starting 2 weeks after chemotherapy ended. The final measurement was 9 months after chemotherapy was finished.

The women ranged in age from 24 to 74 and 60% of them had lumpectomy. About 30% of the women were smokers. Characteristics of the cancers were:

  • 48% were smaller than 2 cm and 37% were 2-5 cm in size
  • 65% were hormone-receptor-positive
  • 82% were HER2-negative

Most of the women had one of two chemotherapy regimens:

  • 44% had either Ellence (chemical name: epirubicin) and Cytoxan (chemical name: cyclophosphamide) (called EC) or fluorouracil, Adriamycin (chemical name: doxorubicin), and Cytoxan (called FAC)
  • 50% of the women had Ellence and Cytoxan followed by Taxol (chemical name: paclitaxel) (called EC+T)

Most of the women (80%) had chemotherapy after surgery. The women who were diagnosed with hormone-receptor-positive disease also were treated with tamoxifen or an aromatase inhibitor. Most of the women (83%) also were treated with radiation therapy.

The researchers found that all the women had normal levels of lymphocytes before chemotherapy started.

There are several different kinds of lymphocytes, including T cells, helper T cells, B cells, and natural killer cells, all of which protect the body against bacterial and viral infections.

Two weeks after chemotherapy ended, the researchers found that levels of T cells, helper T cells, B cells, and natural killer cells had dropped dramatically.

Nine months after chemotherapy ended, levels of some kinds of lymphocytes had returned to normal. Still, the researchers said that chemotherapy seemed to have a long-term effect on:

  • B cells -- cells that ultimately produce antibodies
  • helper T cells -- cells that help with antibody production

Six months after chemotherapy ended, levels of B cells and helper T cells were only at 65% of their original levels, and these levels hadn’t gone up when the researchers measured them 3 months later, 9 months after chemotherapy ended.

The women’s levels of antibodies against the bacteria that can cause tetanus and pneumonia were lowered by chemotherapy and stayed low even 9 months after chemotherapy ended. So even if the women had received a tetanus or pneumonia vaccine, they might still be susceptible to the infections. The researchers said that more studies need to be done to figure out if women who’ve been treated with chemotherapy would benefit from being revaccinated.

The researchers also looked to see if one chemotherapy regimen affected the immune system more than the other.

The EC/FAC regimen was more damaging to B cells and helper T cells at first, but both types of lymphocytes returned to normal levels after chemotherapy ended. The EC+T regimen lowered levels of all the measured lymphocytes and these lower levels continued even after chemotherapy ended.

Smoking also seemed to slow down immune system recovery after chemotherapy. Women who smoked had lymphocyte levels that were about half their original levels 9 months after chemotherapy ended. Women who didn’t smoke had lymphocyte levels that were about 80% of their original levels 9 months after chemotherapy ended.

"We were surprised that the impact of chemotherapy is so long lived,” said Thomas Hughes of the School of Medicine at the University of Leeds and the lead author of the paper. “We also were surprised that smoking and choice of chemotherapy agent influenced the dynamics of the recovery of the immune system. We might need to take into account the future immune health of breast cancer patients when planning treatments, but more research is needed to determine whether this would improve patient outcomes."

If you’ve been diagnosed with breast cancer and will be having chemotherapy treatment, you may be wondering if there are things you can do to boost your immune system to help it recover. We don’t have good evidence that there’s anything you can do to boost your immune system. Still, there’s a growing body of evidence that suggests you can take steps to help your immune system do its job, including:

  • getting 7 or more uninterrupted hours of sleep per night
  • eating a healthy diet that’s full of fresh, whole foods and avoid processed foods and foods with added sugar and salt
  • exercising daily at the highest intensity you can
  • reducing stress through meditation, yoga, massage, support groups or other techniques

For more information, including how to protect yourself against infection, visit the Understanding Your Immune System pages.

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