Cancer pain is undertreated despite a good access to opioids in France. Although many factors are involved, the barriers related to the patient (and his family) are often reported .the reluctance of the patient or the family to take the prescribed medication is linked to misconceptions about the opioids , cultural barriers; or the lack of explanations provided by the physician. Some patients can have undiagnosed slight cognitive impairment .The situation is now more complicated as appear on the market the new form of opioids for the cancer breakthrough pain drug, adding one more opioid formulation in the prescription. The goal of the study is to measure the adherence to opioids in cancer out patients and the associated factors.