The announcement of the cancer diagnosis and his treatment is an important moment in the set up of the doctor–patient relationship. The law of contracts has long governed the relationship between the doctor and the patient. But the legislature clearly demonstrated its will to consider the patient as full actor of his health, leaving the regime of medical decision, the shared decision. This shared decision is based on an obligation to inform the patient on his health and knows many exceptions (minor patients or adults under guardianship, emergency). In Oncology, the medical decision is a decision coordinated between doctors in the multidisciplinary consultation meetings. This decision is considered as a guarantee of the quality of the medical care. It does not preclude the time of the doctor–patient relationship.