Immunotherapy is a relatively recent treatment option that is used for an increasing number of cancers. Most cancer experts now consider immunotherapy to be one of the greatest breakthroughs in cancer therapy in many decades, probably since chemotherapy was first used more than 60 years ago.
Immunotherapy is now an established treatment options for several cancers including melanoma, kidney, bladder and lung cancers, but there are ongoing clinical trials in most cancers, and advances in the field are showing promise in many cancers where previous treatment options were limited.
How does immunotherapy work?
Immunotherapy works by encouraging the body's own self-defence mechanism – the immune system – to fight cancer cells more effectively. Often when a cancer has become established in the body, the immune system stops recognising the cancer cells and effectively stops fighting them. A range of different drugs have now been developed to encourage the immune system to work more effectively against cancer cells.
There are several types of immunotherapy including:
Immune checkpoint inhibitors
These are antibodies that attach themselves to cancer cells or immune cells in the body as a form of 'flag’ to allow the immune system to be re-activated and therefore destroy the abnormal and ‘foreign’ cancerous cells.
This is where white blood cell proteins involved in the immune response – 'cytokines' – are used to try and stimulate an immune response.
Cancer vaccines are of two types – 'prophylactic' (preventative) vaccines that stop infections linked to certain types of cancer, and 'therapeutic' vaccines that encourage the immune system to recognise or respond to cancer cells.
Immunotherapy can be delivered in a variety of different ways, but the most commonly used drugs are given as an intravenous infusion directly into the bloodstream. Immunotherapy, similar to other cancer therapies are given in treatment cycles, that is a treatment followed by a rest period, usually every 2-4 weeks and repeated as required.
Immunotherapy sometimes causes side effects, but are generally better tolerated than many conventional/traditional chemotherapy approaches. The most common side effects of immune checkpoint inhibitors include fatigue which is usually mild but can be more severe when multiple drugs are used, dry or itchy skin, and effects on the thyroid gland (under or overactivity). Less commonly, many other organs can also be affected including the gastro-intestinal system causing diarrhoea, inflammation of the joints or muscles causing aches, liver inflammation (hepatitis), and lung inflammation. The type and frequency of potential side effects depend on the type of treatment given and whether one drug only, or a combination of drugs is being used.
How successful is immunotherapy?
Immunotherapy does not work for all patients – however one trial has shown that around 60% of patients with advanced stage melanoma see their tumours shrink in size (in a trial of Ipilimumab and Nivolumab involving a group of 945 patients).
What has made immunotherapy such a major breakthrough is that patients who have a response to immunotherapy, especially those who achieve a significant response, can maintain this for long periods of time, up to ten years or more in patients with melanoma who had advanced disease initially but remain disease free for extended periods. Some may indeed have been cured of what was previously thought to be incurable disease, although longer periods of follow up will be needed until we know whether this is really cure or just extended remission.
Although immunotherapy treatments show great promise, immunotherapy drugs are funded in Australia for only a small proportion of patients with melanoma, lung and kidney cancers. Cost of unapproved drugs is currently a major obstacle, with treatments not covered by the PBS being prohibitively costly for most people.