Chemo weakens the immune system for up to nine months, especially in smokers, one study finds
Most cancer patients know that chemotherapy weakens their immune systems, putting them at risk for viral and bacterial infections.
A month or two after chemo ends, however, most people assume their immune system has returned to normal. Now, new research suggests that the effects of chemotherapy can compromise part of the immune system for up to nine months after treatment, leaving patients vulnerable to infections – at least when it comes to early-stage breast cancer patients who’ve been treated with a certain type of chemotherapy.
The small, observational study, conducted at the U.K.’s University of Leeds and Leeds Teaching Hospitals NHS Trust, also demonstrated that smoking exacerbates this effect.
“This study has demonstrated that the adaptive immune system is altered following chemotherapy for at least nine months post-therapy,” the authors wrote in their study, published Tuesday in the journal Breast Cancer Research. “We were surprised that the impact of chemotherapy is so long-lived."
Researchers looked at the immune systems of 88 breast cancer patients, measuring their levels of lymphocytes – white blood cells that work together to fight viral and bacterial infections – before and up to nine months after receiving chemotherapy. Predictably, the level of lymphocytes, which included various types of NK (or natural killer cells), T cells and B cells, dropped significantly after chemo, but the impact was short-term. Nine months later, most of the immune cells were up and running at pre-chemo levels.
When it came to certain types of NK, T and B cells, however, the researchers found chemo had a long-term effect. After nine months, B cells (important for creating antibodies) and CD4 T cells (also known as helper T cells) had only “partial recovery,” reaching only 69 percent and 60 percent of pre-chemo levels respectively, potentially leaving patients vulnerable. In smokers, B cell recovery “was substantially and significantly impaired,” the researchers wrote, reaching only 51 percent of pre-chemo levels after 9 months.
Dr. Steve Pergam, an infectious disease researcher at Fred Hutchinson Cancer Research Center and director of infection control at Seattle Cancer Care Alliance, said the study results were “not totally surprising.”
“I think many of us who look at infections do see that there are late infections that occur in patients and we don’t always understand why they occur,” he said. “Generally, the risk we see is in our bone marrow transplant patients. It’s really well documented that they have a delayed immune recovery after that process. With solid tumor malignancies like breast cancer, this study suggests there are potential similarities to a lesser degree.”
But Pergam was quick to point out that this was a preliminary study, that different chemotherapies have different effects on the immune system and that the therapies used during the study period, June 2011 to January 2012, might be different from therapies used now.
He also noted that the decreased immune function observed by researchers might not make that much of a difference to breast cancer patients’ health.
“They’re decreased, but the question is, are they decreased enough to affect clinical risk for infection?” he said. “Let’s say somebody has 4,000 CD4 cells and it’s a 50 percent reduction. They still have 2,000, plenty of CD4 cells for an appropriate immune response.”
Researchers found that the type of chemo used did seem to make a difference in the recovery of patients’ immune systems.
For instance, lymphocyte levels in patients treated with certain anthracycline-based regimens (in this case, epirubicin and cyclophosphamide) followed by the taxane docetaxel (also known as taxotere) “remained significantly depressed,” measuring at 64 percent of pre-chemo levels.
Dr. Julie Gralow – a breast cancer oncologist at SCCA, Fred Hutch's treatment arm – said she thought patients would be very interested in the study, but she felt the “clinical implications of the finding remain to be seen,” noting that the study looked at chemo agents that may not be commonly used in the U.S.
At the SCCA, for example, “We don’t use epirubicin as the anthracycline, we use doxorubicin,” she said. “And when we give anthracyclines, we generally favor taxol over taxotere as the taxane. So we don’t give the same chemo.”
She also suggested that while the study showed the immune system was impacted by chemo, the study didn’t prove that patients were more at risk for infection.
“Most of the effect has recovered within nine months, if you don’t smoke,” she said. “[But] it seems that smoking has a big effect, and we always encourage patients to stop smoking.”
While the researchers did not investigate this effect in other cancers, they said patients treated with the same chemotherapy agents would most likely experience the same thing.
“We have no reason to believe that it would vary according to different cancer types treated with the same chemotherapy regimen, although that was beyond the scope of this current study,” said lead author Dr. Clive Carter of the University of Leeds School of Medicine via email.
Pergam said he was not convinced “we can extrapolate this yet” but added that he would love to see further studies into the long-term effects of chemotherapy on cancer patients’ immune systems.
“This is an emerging area of interest especially as cancer patients are living longer,” he said. “Most of the focus has been around the period where patients are most at risk, when they’re actively in treatment. But it’s important for us to understand the long-term complications.”
In the meantime, Pergam said patients (and their loved ones) may want to be mindful that post-chemo, the body’s immune system is still repairing itself.
“This isn’t saying you can’t go back to leading a normal life,” he said. “I don’t want people to socially isolate themselves. You just need to be more cautious and make sure you get your preventive care.”
He also offered the following chemo recovery tips:
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Diane Mapes is a staff writer at Fred Hutchinson Cancer Research Center. She has written extensively about health issues for NBC News, TODAY, CNN, MSN, Seattle Magazine and other publications. A breast cancer survivor, she also writes the breast cancer blog doublewhammied.com. Reach her at firstname.lastname@example.org.