EORTC Metastatic Breast Cancer Module Development

Inclusion Criteria: * Adult females aged 18 years or over. * Have a diagnosis of MBC (Breast cancer that has spread to another part of the body), including de novo MBC patients. Patients with brain metastases will be included, providing there is no associated major cognitive impairment. * Have received (patients under observation) or currently receiving treatment for MBC, including chemotherapy, hormone therapy, targeted agents (anti-HER2, CDK4/6 inhibitors, mTOR/PIK3CA inhibitors, PARP inhibitors, immune therapy), radiotherapy and combinations. * Conversant in the language of questionnaire administration. * Have the capacity to give informed consent. Exclusion Criteria: * Patients diagnosed with early stage breast cancer. * Patients with any psychiatric condition or cognitive impairment, as determined by the treating physician, that would hamper participation in interviews. * Patients previously involved in Phase I.