Somatic mutations leading to cancer are related to endogenous or exogenous DNA damaging processes. The resultant mutations can be separated into two categories - (i) mutations that provide selective advantage for clonal expansion and (ii) mutations that do not result in growth advantage [12]. The latter have been termed passenger mutations, while the former are referred to as driver mutations. It is widely believed that the number of driver mutations in a cancer sample is limited to a handful, usually two or more but less than ten [13]. In contrast, the genome of a cancer can harbour more than a million somatic mutations [14] most of which are considered to be passengers.