Metastatic breast cancer—breast cancer that has spread from the breast to other parts of the body—is the most common invasive cancer in women.⁵ It comprises more than one-fifth of invasive cancers in women and 16 per cent of all female cancers.⁵ The prognosis of metastatic breast cancer is often poor; distant metastases are the cause of about 90 per cent of deaths due to breast cancer.⁶ Around 15 to 30 per cent of breast cancers are HER2-positive,⁷ and amplification of the HER2 gene is associated with aggressive biological behaviour and a poorer prognosis.⁸ Clinically, HER2-positive disease often features poorly differentiated, high-grade tumours, lymph node involvement, increased rates of cell proliferation and a relative resistance to certain types of chemotherapy. As a result, HER2 is an important target for therapy.⁹

Notes to editors:

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