A system approach termed P4 medicine has recently been proposed in the field of oncology. This approach has been advanced as an extension of what is usually called ‘personalized’ or ‘genomic medicine’. P4 medicine creates effective predictive, personalized, preventive and participatory models to treat patients. In order to give more relevance to the behavioural component that impinges on the way individuals act to prevent, cope and react to illnesses, how they decide between different therapeutic options and interact with physicians and adhere to treatment, we propose that P4 medicine should be transformed into P5 medicine. The fifth P represents the psycho-cognitive aspects to be considered in order to empower the patient, increase his/her quality of life and transform him/her from a passive recipient into an active decision-maker in the treatment process.