SEQUence of Endocrine Therapy in Advanced Luminal Breast Cancer (SEQUEL-Breast)

Inclusion Criteria: * Adult women and men (≥ 18 years of age) with proven diagnosis of adenocarcino-ma of the breast withlocoregional recurrent or metastatic disease not amenable to resection or radiation therapy with curative intent andfor whom chemotherapy is not clinically indicated * Estrogen receptor (ER) expression \>10% and/or progesterone receptor (PR) expression \>10% breast cancerbased on local la-boratory results. Tumor must be HER2- as defined by ASCO-CAP guidelines * Patients must have progressed on fulvestrant as a preceding treatment line (as first or second line therapy) * Previous treatment with a CDK4/6 inhibitor in the advanced setting * The presence of an activating PIK3CA mutation * Evaluable disease\* as defined per RECIST v.1.1 * Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0, 1 or 2 Exclusion Criteria: * Patients with advanced, symptomatic, visceral spread, who are at risk of life-threatening complications in theshort term * Known active uncontrolled or symptomatic CNS metastases, carcinomatous meningitis, or leptomeningealdisease as indicated by clinical symptoms, cerebral edema, and/or progressive growth * Prior treatment with a PI3K /AKT/mTOR inhibitor * Type 1 diabetes or uncontrolled type 2 diabetes (Hba1C \> 68 mmol/mol) * Clinically significant, uncontrolled heart disease and/or recent cardiac events