Advanced cancer typically involves multiple symptoms and seriously affects patients´ quality of life. Anxiety and depression are common. Medical care for patients with advanced cancer should be aimed at symptom control, psychosocial support, spiritual needs, and practical issues. Patients’ preferences regarding care should be central. Open and respectful communication are of key importance, but have been found to be a challenge for health care professionals as well as patients and relatives. Advance care planning (ACP) is a formalised process of communication between patients, relatives and caregivers about patients’ care preferences. It raises awareness of the need to anticipate future deterioration of health. ACP can improve current and future health care decision making, provide patients with a sense of control, increase adequate symptom control and improve quality of life.This project aims to study the effects of formalized ACP on symptom burden and quality of life of patients with advanced cancer. In a phase III multicentre cluster randomized controlled trial at least 20 hospitals in 6 countries will be randomized to provide patients with advanced cancer with either ACP or ‘care as usual’. 1334 patients diagnosed with lung or stage IV colorectal cancer will be included. Patients will fill in questionnaires at inclusion, and at 2.5 and 4.5 months post-inclusion. A relative will fill in a questionnaire after the patient’s death. Use of medical care will be assessed through medical files. Primary endpoints are quality of life (QLQ-C30 emotional functioning) and symptoms at 2.5 months post-inclusion. Secondary endpoints are the extent to which care as received was in line with patients’ preferences, patients’ evaluation of the decision making process, quality of dying and cost-effectiveness of the intervention. Our project will assess the impact of ACP on quality of life, and contribute to improving comfort and quality of care for patients with advanced cancer.