Clinical Trial Finder

Inclusion Criteria:

Patients will be eligible for study participation only if they comply with the following criteria: 1. Written informed consent prior to beginning specific protocol procedures, including expected cooperation of the patients for scheduled visit, the treatment and follow-up, must be obtained and documented according to the local regulatory requirements. 2. Female or male patients. 3. Age at study entry of at least 18 years. 4. Centrally confirmed locally advanced or metastatic breast cancer that is HR-positive (ER and/or PgR ≥ 10% of stained cells at IHC) and HER2-negative (IHC 0 or 1+, or 2+ and ISH negative according to ASCO/CAP guidelines). 5. Patients with deleterious or suspected deleterious g/tBRCA1/2 and/or g/tPALB2 mutations, detected upon local testing. 6. Willingness and ability to provide archived formalin fixed paraffin embedded tissue (FFPE) block or a partial block from archived tumor or metastasis. 7. Patients who received at least one prior line of chemotherapy or endocrine-based therapy for irresectable, locally advanced, or metastatic disease, or patients with recurrent, unresectable, locally advanced, or metastatic disease after adjuvant treatment with CDK4/6 inhibitor therapy. 8. Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-2. 9. Resolution of all acute toxic effects of prior anti-cancer therapy including endocrine therapy or surgical procedures to NCI CTCAE version 5.0 grade ≤ 1 (except alopecia or other toxicities not considered a safety risk for the patient at investigator's discretion). 10. Life-expectancy > 6 months. 11. For female patients: patients need to be either A) of non-childbearing potential (documented postmenopausal or post hysterectomy or surgical sterilization), or B) of childbearing potential with negative serum or urinary pregnancy test within 72 hours before starting treatment in this study (in this case, patients need to use highly effective non-hormonal contraceptive methods as specified in the protocol). For male patients: during the intervention period and for at least 120 days after the last dose of study treatment, patients should refrain from heterosexual intercourse or use a condom (and should also be advised of the benefit for a female partner to use a highly effective method of contraception as a condom may break or leak), and they should refrain from donating sperm.

Exclusion Criteria:

Patients will be ineligible for study participation if they fulfill any of the following criteria: 1. Known hypersensitivity reaction to one of the compounds, excipients, or substances used in this protocol. 2. Active or newly diagnosed CNS metastases, including leptomeningeal carcinomatosis, carcinomatous meningitis, or radiographic signs of CNS hemorrhage. Note: Patients with stable brain metastases are allowed. Radiotherapeutic treatment must be completed 1 week before planned day 1 of study therapy. 3. Presence of symptomatic metastatic visceral disease that are at risk of life-threatening complications in the short term, including but not confined to massive uncontrolled effusions (peritoneal, pleural, pericardial), pulmonary lymphangitis, or fulminant liver involvement. 4. Inadequate organ function prior to enrolment including:

• - Hemoglobin < 9 g/dL (< 5.6 mmol/L) - Absolute neutrophil count (ANC) < 1500/mm³ (< 1.5 x 109/L) - Platelets < 100,000/mm³ (< 100 x 109/L) - Alanine aminotransferase (ALT/SGPT) and/or aspartate aminotransferase (AST/SGOT) > 3 x upper normal limits (ULN).

If the patient has liver metastases, ALT and AST should not be ≥ 5 x ULN.

• - Alkaline phosphatase (ALP) > 2.5 x ULN.

• - Total serum bilirubin > 1.5 x ULN (exception: patients with Gilbert's syndrome permitted up to ≤ 3 x ULN) - Serum creatinine > 1.5 x ULN or estimated creatinine clearance < 50 mL/min as calculated using the standard method for the institution.

5. Existing contraindication against the use of the elacestrant or niraparib. 6. Prior treatment with PARP inhibitors. 7. Female patients: pregnancy or lactation at the time of randomization or intention to become pregnant during the study and for a predefined period after the end of treatment (as described in protocol). Male patients: intention to get a child during the study and for a predefined period after the end of treatment (as described in protocol). According to the treatment received during the study, required contraception timelines for female and male patient after the end of therapy differ (refer to the study protocol). 8. Any of the following within 6 months prior to enrolment: myocardial infarction, severe/unstable angina, ongoing grade ≥ 2 cardiac dysrhythmias, prolonged QT corrected by Fridericia's formula (QTcF) grade ≥ 2, uncontrolled atrial fibrillation of any grade, coronary/peripheral artery bypass graft, heart failure of New York Heart Association (NYHA) Class II or greater, or cerebrovascular accident including transient ischemic attack. 9. Uncontrolled hypertension at the time of screening (systolic BP > 140 mmHg or diastolic BP > 90 mmHg that has not been adequately treated or controlled). 10. Active and current anticoagulation for treatment purposes of thrombotic events occurring <6 months before enrolment is not allowed (prophylactic anticoagulation, however, is acceptable). Treatment with an anticoagulant for a thrombotic event occurring > 6 months before enrolment, or for an otherwise stable and allowed medical condition (e.g., well controlled atrial fibrillation) is acceptable, provided dose and coagulation parameters (as defined by local standard of care) are stable for at least 28 days prior to the first dose of study drug. 11. Known difficulty in tolerating oral medications or conditions which would impair absorption of oral medications such as: uncontrolled nausea or vomiting (i.e., CTCAE ≥ grade 3 despite antiemetic therapy), ongoing gastrointestinal obstruction/motility disorder, malabsorption syndrome, or prior gastric bypass. 12. History of endometrial intraepithelial neoplasia in patients who have not undergone a hysterectomy. 13. Malignant disease other than breast cancer, active or being disease-free for less than 5 years (except carcinoma in situ of the cervix, DCIS, and non-melanomatous skin cancer adequately treated). 14. Any known history of myelodysplastic syndrome (MDS) or a pretreatment cytogenetic testing result at risk for a diagnosis of MDS/acute myeloid leukemia (AML). 15. Increased bleeding risk due to concurrent conditions (e.g., major injuries or major surgery within the past 28 days before start of study treatment). 16. Received a transfusion (platelets or red blood cells) within 4 weeks before the first dose of study treatment. 17. Received radiotherapy encompassing > 20% of the bone marrow within 2 weeks, or any radiation therapy (including radiation therapy for CNS metastases) within 1 week before planned day 1 of study therapy. 18. Uncontrolled significant active infections including HBV, HCV, and/or HIV. Patients with a positive hepatitis B surface antigen result or a positive hepatitis C antibody test result at screening or within 3 months before first dose of study treatment are excluded, except for the following:

• - Participants with positive anti-HBs antibody titer and confirmatory negative hepatitis B DNA polymerase chain reaction.

• - Participants with positive hepatitis C antibody due to prior resolved disease can be enrolled only if they have both completed curative therapy and have a hepatitis C viral load < quantifiable limit.

19. Current active pneumonitis or any history of pneumonitis requiring steroids (any dose) or immunomodulatory treatment within 90 days of planned start of the study. 20. Any severe, acute, uncontrolled, or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation or investigational or non-investigational products administration, or may interfere with the interpretation of study results, and, in the judgment of the investigator, would make the patient inappropriate for entry into this study. 21. History of significant neurological or psychiatric disorders including psychotic disorders, dementia, or seizures that would prohibit the understanding and giving of informed consent. Also, prior history of posterior reversible encephalopathy syndrome (PRES) excludes patients from this study. 22. Unable or unwilling to avoid medications, supplements (e.g., St. John's wort), or foods (e.g., grapefruit, pomegranate, pomelos, star fruit, Seville oranges and their juices) that are moderate/strong inhibitors or inducers of CYP3A4 activity. Participation will be allowed if the medication, supplements, or foods are discontinued for at least 14 days prior to study entry and for the duration of the study. 23. Concurrent treatment with other experimental drugs. Participation in another clinical trial with any investigational not marketed drug within 30 days prior to study entry. 24. Receipt of live attenuated vaccination within 30 days prior to study entry. COVID-19 vaccines that do not contain live viruses are allowed (at least one week prior to study entry).

Patients with HR-positive, HER2-negative advanced or metastatic breast cancer and g/tBRCA1/2 and/or g/tPALB2 mutations have a low progression-free survival (PFS) and represent a patient population with a high unmet need, hence further treatment options should be explored to improve patient outcomes. Elacestrant is a novel, nonsteroidal, orally bioavailable estrogen receptor antagonist (SERD) that has shown efficacy in heavily pretreated patients with HR-positive, HER2-negative breast cancer, and in those with ESR1 mutations known to confer endocrine resistance, and has thus gained approval in 2023 by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for postmenopausal women or adult men with ER-positive, HER2-negative, ESR1-mutated advanced or metastatic breast cancer with disease progression following at least one line of ET. Niraparib is a poly-adenosine diphosphate ribose polymerase (PARP) inhibitor that has shown promise in patients with gBRCA mutated, HER2-negative locally advanced or metastatic breast cancer, previously treated with ≤2 prior lines of chemotherapy, as well as in patients with platinum-sensitive, recurrent ovarian cancer, regardless of the presence or absence of gBRCA1/2 mutations, with moderate bone marrow toxicity. The purpose of the proposed study is to investigate if the addition of elacestrant to niraparib could potentially lead to an improvement in PFS compared to niraparib alone in patients with HR-positive, HER2-negative locally advanced or metastatic breast cancer with g/tBRCA1/2 and/or g/tPALB2 mutations. ELEMENT is a phase II, prospective, multi-center, randomized, open label, parallel group study in patients with HR-positive, HER2-negative locally advanced or metastatic breast cancer with g/tBRCA1/2 or g/tPALB2 mutation, with 2:1 randomization into Arm A (niraparib + elacestrant) or arm B (niraparib). Treatment in either arm will be given until disease progression, unacceptable toxicity, withdrawal of patient´s consent to study participation, or end of study.

Arms

Experimental: Arm A: Niraparib + elacestrant*

Treatment will be given until disease progression, unacceptable toxicity, withdrawal of patient´s consent to study participation, or end of study. * Together with GnRH analogue in pre- and perimenopausal women, and in men, at least two weeks prior to treatment. Elacestrant tablets 400 mg orally daily Niraparib 200 mg orally daily The protocol provides procedures for specific adverse events requiring dose modifications or delays.

Active Comparator: Arm B: Niraparib

Treatment will be given until disease progression, unacceptable toxicity, withdrawal of patient´s consent to study participation, or end of study. • Niraparib 200 mg orally once daily The protocol provides procedures for specific adverse events requiring dose modifications or delays.

Interventions

Drug: - Niraparib + Elacestrant

Niraparib 200mg orally daily and elacestrant 400mg orally daily

Drug: - Niraparib

Niraparib 200mg orally daily