New research that looks at the long-term effects of chemotherapy on breast cancer survivors finds it weakens parts of the immune system for at least 9 months after treatment. This could leave patients with insufficient resilience to common infections, such as pneumonia and tetanus, even if they were immunized previously, say the researchers. Share on Pinterest Chemotherapy works by attacking cells that divide quickly. But cancer cells are not the only cells that do this – some cells in the immune system also divide quickly, such as those made in the bone marrow. The study – published in the journal Breast Cancer Research – comes from the University of Leeds and Leeds Teaching Hospitals NHS Trust in the UK. One of the senior authors, Thomas Hughes, an associate professor in the Faculty of Medicine at Leeds, says: “We were surprised that the impact of chemotherapy is so long lived.” He and his colleagues suggest the findings indicate breast cancer survivors who have undergone chemotherapy would likely benefit from post-treatment monitoring. Breast cancer is the most common cancer in women and claims over half a million lives worldwide every year, note the authors. Typical treatment for primary tumors involves surgery to remove the tumor, combined with other therapies, such as hormone therapy, radiotherapy and/or chemotherapy to kill any remaining cancer cells. Around 30% of breast cancer patients receive chemotherapy. Chemotherapy drugs work by attacking cells that divide quickly, which is what cancer cells do. But other cells – such as those in the bone marrow where white blood cells are made – also divide quickly and are likely to be affected by chemotherapy.

Some lymphocytes and antibodies stayed weak for 9 months For their study, the researchers monitored 88 primary breast cancer patients at various intervals from 2 weeks to 9 months after chemotherapy completion. They also had data on all but 26 of the patients before they started chemotherapy. They monitored levels of various parts of the immune system, including antibodies and a group of white blood cells called lymphocytes. The data showed that levels of major lymphocytes, such as T cells, B cells and natural killer cells – which protect against infection by viruses and bacteria – fell significantly following chemotherapy. The effect was only short term for most types of lymphocyte – they returned to pre-chemotherapy levels by the 9-month mark. But the B cells and helper T cells only returned to 65% of their pre-chemotherapy levels by 6-month mark, and they were still at that level 3 months later. B cells are important for producing antibodies, and T helper cells assist in that task. Antibodies are important for helping the immune system identify and eliminate pathogens like viruses and bacteria. There are different antibodies for different pathogens. The team also found that levels of antibodies against the types of bacteria that cause tetanus and pneumonia fell following chemotherapy and were still reduced at the 9-month mark.