Trial of BKM120/Tamoxifen-combination in Patients With HR-pos, HER2-neg Breast Cancer

Inclusion Criteria: * Patient has histologically and/or cytologically confirmed diagnosis of breast cancer * Patient has radiologic or objective evidence of inoperable locally advanced, or metastatic breast cancer * Patient has a known hormone receptor status HR-positive (ER and/or PR positive) and HER2-negative status * Patient has a representative archival formalin-fixed tumor biopsy (metastasis or primary tumor) * Patient has prior exposure to antihormonal therapy * Patient has received ≤ 2 prior antihormonal treatments in the metastatic setting * Prior treatment with tamoxifen in the (neo-)adjuvant setting is allowed but has to be discontinued for at least 1 year. * Patient may have received up to one prior chemotherapy in the metastatic setting * Measurable or non-measurable lesions according to RECIST v1.1 criteria * Patient has an Eastern Cooperative Oncology Group (ECOG) performance status score ≤ 2 Exclusion Criteria: * Patient has received previous treatment with a PI3K- or AKT-inhibitor or mTOR-inhibitors * Prior treatment with Tamoxifen in the metastatic setting. Treatment with tamoxifen in the (neo-)adjuvant setting is allowed, but has to be discontinued for at least 1 year * Patient has symptomatic CNS metastases * Patient has a medically documented history of or active major depressive episode, bipolar disorder (I or II), obsessive-compulsive disorder, schizophrenia, a history of suicidal attempt or ideation, or homicidal ideation (e.g. risk of doing harm to self or others), or patients with active severe personality disorders (defined according to DSM-IV). * Patient has a known history of HIV infection (testing not mandatory) infection