Cancer heterogeneity and “The Struggle for Existence”: Diagnostic and analytical challenges

► We discuss the challenges presented by intra tumour heterogeneity (ITH). ► We present the current evidence for the existence of intra tumour heterogeneity and also some examples of its absence. ► We examine in detail the problems faced in calling point mutations and present some possible solutions. ► The implications of ITH on mechanisms underlying the acquisition of drug resistance are discussed.