The drug could improve the clinical outcome in some patients with head, neck or prostate cancer, compared to the current standard of chemotherapy. The new drug also appears to have fewer side-effects.
While typical chemotherapy involves directly killing cancer cells, immunotherapy anti-cancer drugs stimulate the body's immune system in to destroying cancer cells. It is currently only used as a standard treatment in some cancers (e.g. melanomas) but can also be used if chemotherapy fails to work. However, a recent trial found that it should be used more often.
Within a group of men with advanced prostate cancer, who had failed to respond to any other treatment, one in 20 saw a reduction in tumour size on pembrolizumab.
One in four patients, with advanced head and neck cancer, saw their cancer stabilise for an average of 23 months, which is longer than the average chemotherapy stabilisation of period of four and a half months. However, currently more patients respond to chemotherapy than to immunotherapy.
Professor Paul Workman, chief executive of The Institute of Cancer Research, describes the biggest obstacle with using immunotherapy: "A limitation with immunotherapy is that there's no good test to pick out those who are most likely to respond."
A recent study, however, has provided some early evidence that a prostate cancer patient's response to pembrolizumab could be predicted by looking at mutations in DNA repair genes. "Lucky" patients who are found to have these mutations could be classified as "super responders" to the treatment and be able to avoid the toxic effects of chemotherapy, something with Professor Workman is very excited about and keen to see studied further.