The process of medical decision implies the elaboration of a choice between alternatives. Who has the choice? The doctor? The patient? Both? That depends on the particular characteristics of the patient and of the tumour, but also of the characteristics of the doctor and of his approach of medical discipline. For that reason, we planned first to remind some principles. In our analysis, the patient-doctor's relationship ties with environment, culture and habits. Philosophical principles, moral, and models of the relation between patient and doctor concern first part. In the second part, these ideas are compared with our routine practice: surveys about patients' needs, the obstacles for complete information and participation, studies on patients' preferences. The authors' analysis is that we are going inescapably towards shared decision-making taking into account the patients preferences. This evolution is not only tied with ethical principles, but with medical reason, i.e. the variability of patients' preferences led to tailor the treatment to the individual patient especially when benefit is limited. Of course, the applicability of a shared model depends on the particular situation of the patient and of his demand. It is all the easier as the consequences of the treatment are well known the riks tiny and distant. In the classical paternalistic model, there is no choice for the patient because the doctor(s) give the treatment. In the ideal model of the shared decision, doctor and patient progress together towards medical decision, in this case, the patient is not alone facing a choice, and in all cases, he is never alone.