PIK3CA/PTEN-altered Advanced Breast Cancer Treated With MEN1611 Monotherapy or in Combination With Eribulin (SABINA)

Inclusion Criteria: Signed Informed Consent Form (ICF) prior to beginning specific protocol procedures. Age ≥18 years at time of signing ICF. Histological confirmed MpBC as per local assessment. Known HR status Prior treatment with at least one, but no more than four, prior lines of systemic therapy for advanced disease. No prior treatment with a PI3K/AKT/mTOR inhibitor. Patient has a PIK3CA mutation or evidence of PTEN loss by immunohistochemistry (IHC) Eastern Cooperative Oncology Group (ECOG) performance status of 0-1. Life expectancy greater or equal to 12 weeks. Unresectable locally advanced/metastatic MpBC documented by computed tomography (CT) scan or magnetic resonance imaging (MRI) Patients with clinically stable metastatic central nervous system (CNS) tumors who are not receiving steroid therapy or anticonvulsant at baseline are not eligible if stereotactic radiotherapy within 7 days prior to initiation of study treatment; whole-brain radiotherapy within 14 days prior to initiation of study treatment; or neurosurgical resection within 28 days prior to initiation of study treatment. Resolution of all acute toxic effects of prior anti-cancer therapy to grade ≤ 1 as determined by the US National Cancer Institute-Common Terminology Criteria for Adverse Events (NCI-CTCAE) version 5.0. Available archival tumor sample (FFPE tissue) of the most recent biopsy/surgery since last progression. No prior treatment with eribulin. Adequate hematologic and organ function within 14 days before the first study treatment on Day 1 of Cycle 1, defined by the following: Hematological (without platelet, red blood cell transfusion, and/or granulocyte colony-stimulating factor support within 7 days before first study treatment dose): White blood cell (WBC) count > 3.0 x 109/L, absolute neutrophil count (ANC) ≥ 1.5 x 109/L, platelet count ≥ 100.0 x109/L, and hemoglobin ≥ 9.0 g/dL (≥ 5.6 mmol/L). Hepatic: Serum albumin ≥ 3 g/dL; total bilirubin ≤ 1.5 times the upper limit of normal (ULN) (≤ 3 x ULN in the case of Gilbert's disease); aspartate transaminase (AST) and alanine transaminase (ALT) ≤ 2.5 × ULN (in the case of liver metastases ≤ 5 × ULN); alkaline phosphatase (ALP) ≤ 2 × ULN (≤ 5 × ULN in the case of liver and/or bone metastases). Renal: serum creatinine ≤ 1.5 x ULN or creatinine clearance ≥ 50 mL/min based on Cockcroft-Gault glomerular filtration rate estimation. Urinalysis: including dipstick (specific gravity, pH, glucose, protein, ketones, and blood) and microscopic examination (sediment, red blood cells [RBC], white blood cells [WBC], casts, crystals, epithelial cells, and bacteria). For women of childbearing potential: agreement to remain abstinent (must refrain from heterosexual intercourse) or use highly effective contraceptive methods, or two effective contraceptive methods, as defined in the protocol, during the treatment period and for at least 7 months after the last dose of study treatment, whichever is longer. Women of childbearing potential must have a negative serum pregnancy test within 7 days before study treatment initiation, and must agree to refrain from donating eggs during the entire study treatment period and for 3 months after the last administration of the study drug. Being male subjects, surgically sterile or having agreed with true abstinence (must refrain from heterosexual intercourse), or whose female partners are willing to agree with true abstinence or use barrier contraceptive measures mentioned above during the entire study treatment period and for 7 months after the last administration of the study drug. Males must agree to refrain from donating sperm during the entire study treatment period and for 3 months after the last administration of the study drug. Patient must be accessible for treatment and follow-up. Measurable, or non-measurable but evaluable, disease (in case of cohort A) and measurable disease (in case of cohort B) as defined by the local site Investigator as per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 (v1.1) criteria. Exclusion Criteria: Current participation in another therapeutic clinical trial. Extra-cranial radiotherapy or limited-field palliative radiotherapy within 7 days prior to study enrolment, or patients who have not recovered from radiotherapy-related toxicities to baseline or grade ≤ 1 and/or from whom ≥ 25% of the bone marrow has been previously irradiated. Major surgery (defined as requiring general anesthesia) or significant traumatic injury within 21 days of start of study drug, or patients who have not recovered from the side effects of any major surgery. Patient with a concurrent malignancy or malignancy within 5 years of study enrollment except for carcinoma in situ of the cervix, non-melanoma skin carcinoma, or stage I uterine cancer. Treatment with approved chemotherapy/immunotherapy/ targeted agents within 21 days prior to initiation of study, or treatment with an investigational cancer therapy for 21 days or 5 half-lives (whichever is longer) prior to initiation of any study treatment. Patient with cerebrovascular accident or transient ischemic attack within 6 months prior to the start of any study treatment. Congenital long QT syndrome or screening QT interval corrected using Fridericia's formula (QTcF) > 480 milliseconds. Patient with an active cardiac disease or a history of cardiac dysfunction or conduction abnormalities including any of the following: Unstable angina pectoris or documented myocardial infarction within 6 months prior to study entry. Symptomatic pericarditis. Documented congestive heart failure (New York Heart Association functional classification III- IV). Left ventricular ejection fraction (LVEF) < 50% as determined by multiple gated acquisition (MUGA) scan or echocardiogram (ECHO). Ventricular arrhythmias except for benign premature ventricular contractions. Supraventricular and nodal arrhythmias requiring a pacemaker or not controlled with medication. Conduction abnormality requiring a pacemaker. Other cardiac arrhythmia not controlled with medication. Patient with uncontrolled hypertension. Uncontrolled diabetes mellitus (glycated haemoglobin [HbA1c] >7%) and/or fasting plasma glucose (FPG) >120 mg/dL or 6.7 mmol/L. Known concurrent severe and/or uncontrolled concomitant medical conditions (i.e. influenza or any other active infections) that could cause unacceptable safety risks or compromise compliance with the protocol. Known active or uncontrolled pulmonary dysfunction. Current known infection with human immunodeficiency virus (HIV), hepatitis B virus (HBV), or hepatitis C virus (HCV). Patients with past HBV infection or resolved HBV infection (defined as having a negative hepatitis B surface antibody [HBsAg] test and a positive hepatitis B core antibody [HBcAb] test, accompanied by a negative HBV DNA test) are eligible. Patients positive for HCV antibody are eligible only if polymerase chain reaction (PCR) is negative for HCV RNA. Known hypersensitivity reaction to any investigational or therapeutic compound or their incorporated substances. Patient with serious and/or unstable pre-existing psychiatric or neurologic illness or other conditions that could interfere with subject safety. History of significant gastrointestinal disease, including but not limited to abdominal fistula, gastrointestinal perforation or other malabsorption syndromes that would impact on drug absorption. Grade ≥ 2 diarrhea should resolve at least 7 days prior to the start of any study treatment. Subject receiving chronic treatment with steroids, as immunosuppressant, or another immunosuppressive agent. Subject receiving treatment with drugs known to be moderate and strong inhibitors or inducers of cytochrome P450 3A isoenzyme (CYP3A) as well as moderate or strong inducers of cytochrome P450 1A2 (CYP1A2) within 2 weeks of the first administration of MEN1611. Breastfeeding or pregnancy as determined by a serum pregnancy test (β-HCG) at screening, prior to the administration of MEN1611 either in monotherapy or in combination with eribulin. Since β-HCG over expression can be also elevated in some tumor types, a positive result should be confirmed with a validated alternative test (e.g., ultrasound).