Currently, GDC-0077, another second-generation PI3K-α inhibitor, is being tested in a phase I clinical trial in patients with PIK3CA mutant solid tumours that are locally advanced or metastatic, including breast cancer, and GDC-0077 is being tested in combination with targeted therapies focused on the ER/PR+Her2– subtype (NCT03006172). Here, ESR1 is linked to breast cancer.