Breast cancer is the most common neoplasm in women, with over 55,000 new diagnoses per year in the United Kingdom.1 The vast majority of patients present with disease localised to the breast and axillary lymph nodes, and are treated with the aim of cure, but for the 6–7% who present with de novo metastatic disease (dnMBC), treatment is usually with palliative intent.1,2 Overall, the median survival of those with metastatic breast cancer (MBC) is 2–3 years,3 although the range is wide, with some patients with ER + or HER2 + disease living much longer. This evidence concerns the gene ERBB2 and neoplasm.