Researchers and doctors know that 1 in 3 of the male population over the age of 50 has cancer cells in their prostate. However, most of these men will never know they have it and it will not affect their quality of life or their life expectancy. However, some cancers can be aggressive. These are more likely to spread outside of the prostate and cause problems. Doctors do not have an accurate way to tell the difference between aggressive cancer and those which will not cause any problems. Even within one prostate some tumours are aggressive and others do not cause a problem during the lifetime of a patient. In fact, even within one tumour, different cells may behave differently. In other words, one part of the tumour may be aggressive and spread, whilst another part of the same tumour does not. This project will try to find out more about what makes different tumours and different parts of the same tumour aggressive or harmless.