Every year, more than 285 000 people are diagnosed with cancer in the United Kingdom, and the current estimate is that more than one in three people will develop a form of cancer at some point in their lifetime. There are more than 200 different types of cancer, but four particular tumour types: breast, lung, colorectal and prostateconstitute over half of all new cases diagnosed (Figure 1.1). Cancer incidence, defined as the number of new cases arising in a period of time, is gender and age specific. In males, prostate cancer is the most prolific, where almost 35 000 new cases were diagnosed in 2004, followed by lung cancer, with around 22 000, and bowel cancer, with around 20 000 new cases per year. However, in females, breast cancer continues to be the most common tumour type, the disease accounting for nearly one in three female cancers, with over 44 000 new cases diagnosed in the year 2004.