Our immune systems are wonderful things, fighting disease for us all the time. Cancerous cells have the ability to switch off an immune system if attacked. We’ve focussed on chemotherapy and radiotherapy amongst other treatments to defend against cancer, but could using our own immune systems (immunotherapy) be the answer?
Naturally the immune system fights to remove unknown or undesirable cells/microbes from our bodies. The immune system can remove cells which are not functioning properly, and does this efficiently most of the time. This process generally works to prevent the development of cancer. However, cancer can develop and does so when:
- the immune system is not strong enough to kill cancerous cells
- the cancerous cells produce signals (i.e. a protein called PD-L1) to stop the immune system from attacking it
- the cancerous cells hide from the immune system
How could immunotherapy change this? Immunotherapy uses drugs to reactivate our own immune systems when they are not fighting disease properly. The treatment has been used for a few cancer types to date, but is usually a third line of defence when other chemotherapy and radiotherapy methods have failed.
However, this month the media covered immunotherapy being used to treat prostate cancer with reasonable success. Prostate cancer is now the second most common cancer in men worldwide, with ~130 new cases diagnosed in the UK every day. Currently, 31 men die every day in the UK due to prostate cancer. These statistics are shocking in such a developed country. Prostate cancer was in fact the first cancer type for which an immunotherapy drug was approved. A recent trial was conducted by the Institute of Cancer Research in London with 258 men who had ‘untreatable’ prostate cancer. These patients tried an immunotherapy drug: pembrolizumab. The drug works to stimulate the immune system to recognise cancerous cells and fight against them as our immune systems normally would when faced with a foreign body. One year after treatment, 1/3 of the candidates in the trial were still alive, and one in ten had no further tumour growth. Overall, the drug increased the men’s survival rates dramatically. Although the drug did not stop tumour growth for all participants, this study has highlighted that for some individuals immunotherapy could be a great treatment.
Why does immunotherapy work for some and not others? Cancer is not the same for everyone, it will vary based on which genes you carry. For example, certain men saw tumour shrinking when given the above immunotherapy drug. These men had specific DNA repair mutations in their genetic code (i.e. for these men, the DNA repair switch had been turned off and thus, resulted in tumour growth). Another study conducted against bowel cancer, demonstrated that patients who had a genetic defect in their DNA repair mechanism had better results from immunotherapy than those who didn’t. Therefore, genetics can help us to deduce who is more likely to be susceptible to cancer development in the first place. If certain cancer types/genetic patterns are shown to respond well to immunotherapy in trials, it could be possible to test a patient for these markers when they present with cancer. Therefore, eventually we could deduce if their cancer is likely to respond well to immunotherapy based in their genetics, avoiding chemo/radiotherapy treatments. Research is currently working to deduce more genetic markers which would indicate if a patient is likely to respond to immunotherapy as a first use treatment, but requires much more testing.
So far, only 20% of all cancer patients are thought to respond to immunotherapy. Although this is not a huge percentage, for patients who could benefit from immunotherapy with first use, this would limit their time spent trying other harsh methods (chemo/radiotherapy) and improve quality of life. Therefore, instead of turning to chemo/radiotherapy at the first sign of cancer, helping to get our own immune systems to recognise cancerous cells again could in fact be the answer for some patients even with terminal prognosis.