The EU has delivered some good news to AstraZeneca's oncology business, approving its oral selective oestrogen receptor degrader (SERD) for breast cancer, even as it faces obstacles on its path to market in the US. It can be used in patients who develop an ESR1 mutation, without disease progression, during standard first-line endocrine therapy, such as an aromatase inhibitor in combination with a CDK 4/6 inhibitor. Specifically, it is looking at data on ESR1 mutations in circulating tumour DNA (ctDNA), specifically how well ctDNA clearance data aligns with efficacy outcomes. Around one in three patients with this form of advanced breast cancer have tumours that develop ESR1 mutations before disease progression. AZ's head of oncology and haematology, Dave Fredrickson, said the EU approval "marks an important shift in the first-line treatment paradigm" for this type of breast cancer and provides "a new standard-of-care to address emerging resistance ahead of disease progression."