Despite the tremendous improvement in early diagnosis and treatment of breast cancer, a large proportion (up to 40%) of patients with breast cancer will eventually develop metastases. Patients with metastatic breast cancer (MBC) have a median overall survival of 2-3 years, and a relative 5-year survival of 34%. Current advances in therapy have extended the life of those patients with MBC, however these patients still suffer (for longer periods) from deleterious side-effects (either related to the disease itself or to the treatment) such as fatigue, pain, nausea and vomiting, insomnia, dyspnoea, emotional, social and cognitive dysfunction. Among all these side-effects, fatigue is the most common and distressing treatment-related side-effect, as up to 90% of patients with MBC experience fatigue over the course of treatment. All these symptoms negatively affect patients’ QoL and thus an urgent solution is needed to help those with advanced breast cancer to “live well” for as long as possible. PREFERABLE’s vision is to improve the standard of care in MBC by improving the quality, effectiveness and cost-effectiveness for patients in a palliative setting using a non-pharmacological intervention combining supervised and unsupervised app-based exercise. Based on the results from a multinational randomised controlled phase 3 clinical trial (EFFECT trial; (cost)- effectiveness study), the different perspectives of patients with MBC on exercising (PERSPECTIVE study), and through mapping the differences in the European healthcare systems, the PREFERABLE project will generate solid and conclusive evidence of the beneficial effect of exercise on cancer-related side effects and patients’ quality of life in the palliative setting. By this, PREFERABLE will contribute towards reshaping medical practice and improving clinical guidelines and recommendations.