ERBB2 and breast cancer: The combination of endocrine therapy with inhibitors of the cyclin-dependent kinases (CDKs) 4 and 6 is firmly established as the standard upfront treatment approach for metastatic luminal/HER2-negative breast cancer; the SOLAR-1 study established the activity of alpelisib, an alpha-specific inhibitor of phosphatidylinositol 3‐kinase (PI3K), when added to fulvestrant in pretreated patients with tumours harbouring PIK3Ca mutations [11].