This chapter discusses how quantified predictions of risk and efficacy, produced and used by artifacts and humans in the field of personalized medicine, reflect forms of power. It reviews a case study of a specific cancer clinical trial in which a personalized method to tailor treatment is applied. The chapter describes the scope and methodology of the research in brief. It also discusses how risk and power are related analytically, focusing on the conceptualization of risk in governmentality studies which draw on Foucault's formulation of power. As implied by Langdon Winner, a detailed understanding of the technological artifact in its social setting is necessary for uncovering its inner political mechanisms. The chapter argues that risk can be viewed as power through the performativity of various artifacts when these are placed in the context of practices which enable them to 'perform'. Objects and discourses can be simultaneously located in an existing set of practices and viewed as performing a calculative action.