How cancer affects your immune system

Posted on 1 October 2020

Cancer cells often get past your body’s defence system because they mimic normal cells. Cancer treatment helps your body fight back – but can also affect your immune response.

Your immune system comprises an intricate network of cells, molecules, tissues, and organs that work hard to prevent infection or disease, including cancer. This remarkably efficient system keeps you healthy by getting rid of pathogens (agents that cause disease) and abnormal cells (such as cancer cells).

‘A healthy immune system attacks “foreign invaders” – cells or organisms it does not recognise,’ says Dr Keorapetse Tabane, a medical oncologist at Sandton Oncology Centre and Mediclinic Morningside. However, as Dr Tabane explains, because cancer cells develop from your own cells, your immune system doesn’t always know it should attack them. In addition, cancer can weaken your immune system by spreading into your bone marrow and preventing it from making infection-fighting white blood cells. ‘Although this happens most often in cases of leukaemia or lymphoma, it can happen with other cancers too,’ says Dr Tabane, adding that certain cancer treatments can also temporarily weaken your immune system.

The most common treatments for cancer are surgery, chemotherapy, radiation therapy and, more recently, immunotherapy and targeted treatments. ‘Immunotherapy harnesses the immune system to fight the cancer, as opposed to chemotherapy which often involves toxic drugs,’ Dr Tabane explains. ‘The benefit of immunotherapy is that the side effects are less severe than those associated with chemotherapy – and the benefits tend to be maintained over a long period. Targeted therapies are specific against certain cancer-driving mutations, taking us into the exciting era of personalised oncology. Some immunotherapy drugs and targeted therapies are already registered and available in South Africa.’

Chemotherapy involves chemical drugs that are designed to destroy cancer cells. It may reduce the number of white blood cells produced by your bone marrow, affecting your body’s ability to fight infection during and after treatment. ‘While chemotherapy affects cancerous and non-cancerous cells, targeted treatment targets cells that harbour a specific cancer-driving mutation,’ says Dr Tabane. ‘The benefit is there is less toxicity compared to chemotherapy and, most cases, better efficacy.’

You are at risk of getting an infection 7 to 14 days after having chemotherapy, when your white blood cell count is at its lowest. Most patients recover their blood counts before the next chemotherapy, but if you experience persistently low blood counts, your doctor can prescribe treatment to boost your blood counts.

‘Radiation therapy is a therapeutic treatment that uses ionising radiation to eradicate or damage cancer cells,’ says Dr Tabane. ‘High energy X-rays or electron beams of varying energies are used in accordance with your doctor’s prescription.’ Local radiation therapy usually has only a mild, temporary effect on your immune system. However, if it is directed at your pelvic bones, where the marrow helps manufacture infection-fighting white blood cells, your immune system might be compromised.

Remember, regular mammograms, colonoscopies, Pap smears, and prostate cancer screening help your doctor detect cancer in its earliest stages, which means it is easier to treat. Don’t delay routine screenings or defer cancer treatment because of Covid-19 concerns. Mediclinic hospitals and emergency centres are equipped to deal with all patients and strict policies and procedures are in place to limit the risk of infection.



Published in Cancer

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