A PoC Study to Evaluate Treatments' Efficacy by Monitoring MRD Using ctDNA in HR-positive/HER2-negative EBC Population

Eligibility criteria for surveillance phase: Note: Participants who had not participated in the surveillance phase but have an additional positive ctDNA test will be eligible for direct-to-treatment phase entry if they fulfill all the matching eligibility requirements. Therefore, these participants will not need to meet all the eligibility criteria for the surveillance phase. Inclusion criteria (surveillance phase): 1. Signed surveillance phase ICF prior to participation in any Study-related activities. 2. Male or female participants aged 18 years or older. 3. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1. 4. Histologically proven primary HR-positive according to the updated American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) 2020 guidelines and HER2-negative BC as per ASCO/CAP 2018 criteria based on local testing on the most recent analyzed biopsy. 5. Participants with high-risk early-stage BC according to at least one of the following criteria: 1. If no previous neoadjuvant chemotherapy: i. pN2-N3, or ii. pN1 (including micrometastasis - pN1mi) if: <!-- --> 1. pT3/T4, or 2. pT2 and high genomic risk, and/or histological grade III, and/or Ki 67 ≥ 30%. b. If participants have received previous neoadjuvant chemotherapy, they must have had residual invasive disease defined as at least one of the following: i. Residual invasive disease in lymph nodes (ypN+, including ypN1mi) ii. ypN0 with residual invasive disease in breast if: <!-- --> 1. cT3/T4, or 2. cT2 and high genomic risk, and/or histological grade III, and/or Ki67 ≥ 30%. Note: Genomic risk using platforms such as Oncotype Dx, Prosigna or Mammaprint won't be assessed for the screening to participate in the Study. However, participants with the detailed scores assessed prior to Study inclusion, may be eligible. 6\. On adjuvant treatment with ET for at least two years and no more than seven years at the time of Study enrolment with an additional three years of ET planned, and at least six months prior to enrolment on the same ET treatment with AI or tamoxifen (LHRH agonist is mandatory for male and premenopausal participants receiving AI or tamoxifen, except in cases of bilateral oophorectomy). Note: Premenopausal and male participants treated with tamoxifen alone are excluded. 7\. Prior treatment with cyclin-dependent kinases 4/6 inhibitors (CDK4/6i) in the adjuvant setting will be allowed in the case of an interval of at least 12 months between the last dose and inclusion in the trial. 8\. No prior treatment with selective estrogen receptor degraders (SERDs) will be allowed. 9\. Availability and willingness to provide the most recently available (archival formalin-fixed paraffin-embedded \[FFPE\]) tumor tissue sample (either from diagnostic biopsy, primary surgery, or where available from a residual disease post-neoadjuvant therapy) at the time of Study inclusion. Note I: Participants with multifocal BC may be enrolled, if archival tissue samples from at least two tumors are available and after histopathological examination, all tumors meet pathologic criteria for HR-positive and HER2-negative BC. Note II: Participants with bilateral carcinoma of the breast may be included as long as at least one of the tumors meets the criteria established by the protocol and both are HR-positive and HER2-negative tumors. 10\. Successful ctDNA assay designability, defined as the ability to generate a personalized, tumor-informed ctDNA assay based on sequencing of tumor tissue and matched germline DNA, enabling longitudinal ctDNA assessment. 11\. Absence of metastatic disease by routine clinical assessment (computed tomography \[CT\] scan of the thorax and abdomen, and bone scan or positron emission tomography \[PET\] scan) confirmed no longer than three months prior to Study inclusion. 12\. Participants must have had surgery for their primary BC with documented clear margins (as per local guidelines), and they must have received radiotherapy if indicated (as per local guidelines). 13\. Participants must be able and willing to adhere to Study procedures. Exclusion criteria (surveillance phase): 1. Participants with pathological complete response (pCR) after neoadjuvant treatment. 2. Receiving or planning to receive any concurrent anti-cancer treatment for the current BC diagnosis, other than permitted adjuvant ET and/or bone-modifying agents (denosumab or biphosphonates). 3. Diagnosis of an alternative cancer in the five years prior to primary BC diagnosis, other than for non-melanoma carcinoma of the skin or cervical carcinoma in situ. Other stage I tumors will be discussed case by case prior to inclusion with the Medical Monitor of the Study. 4. Active or prior documented inflammatory bowel disease (i.e. Crohn's disease, ulcerative colitis, or a preexisting chronic condition resulting in baseline grade ≥ 1 diarrhea) that may significantly alter the absorption of oral drugs. 5. Active cardiac disease or history of cardiac dysfunction including any of the following: a. History (within two years from screening) or presence of idiopathic bradycardia or resting heart rate \< 50 beats per minute at screening. b. History of angina pectoris or symptomatic coronary heart disease within 12 months prior to Study entry. c. QT interval corrected through use of Fridericia's formula (QTcF) \> 450 ms for women and \> 470 ms for men by at least three electrocardiograms (ECGs) \> 30 minutes apart. d. History or presence of an abnormal ECG that is clinically significant in the investigator's opinion, e. History of ventricular dysrhythmias or risk factors for ventricular dysrhythmias such as structural heart disease (e.g. severe left ventricular systolic dysfunction, left ventricular hypertrophy cardiomyopathy, infiltrative cardiomyopathy, moderate-to-severe valve disease), coronary heart disease (symptomatic or with ischemia demonstrated by diagnostic testing), clinically significant electrolyte abnormalities (e.g. hypokalemia, hypomagnesemia, hypocalcemia), or family history of long QT syndrome within 12 months. 6. History of pneumonitis, interstitial lung disease (ILD), or pulmonary fibrosis. 7. Known history of Human Immunodeficiency Virus (HIV) infection. 8. Clinically significant liver disease consistent with Child-Pugh C, including current known infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), current alcohol abuse, or cirrhosis. Participants with past HBV infection or resolved HBV infection (defined as having a negative hepatitis B surface antigen \[HBsAg\] test and a positive hepatitis B core antibody \[HBcAb\] test, accompanied by a negative HBV DNA test) are eligible. Participants positive for HCV antibody are eligible only if polymerase chain reaction (PCR) is negative for HCV RNA. 9. Active bleeding diathesis venous thrombo-embolism, previous history of bleeding diathesis or chronic anti-coagulation treatment, or any indications or history of Disseminated Intravascular Coagulation (DIC) or Deep vein thrombosis (DVT). Low molecular weight heparin (LMWH), low dose aspirin or clopidogrel are permitted. 10. Creatinine clearance \< 30mL/min. 11. Participants with renal dysfunction who require dialysis. 12. Participant who has any other concurrent severe and/or uncontrolled medical condition that would, in the Investigator' opinion cause unacceptable safety risks, contraindicate participation in the clinical trial or compromise compliance with the protocol. 13. Females who are known to be breastfeeding or pregnant as determined by a serum pregnancy test, Human chorionic gonadotropin (β-HCG), prior to the administration of any trial treatment (once during the treatment phase). 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). 14. Female or male participants planning a pregnancy. 15. Participation in another interventional clinical trial within 28 days prior to screening or concurrent participation in another interventional clinical trial. Eligibility criteria for participant entry into the treatment phase: Inclusion criteria (treatment phase): A. Inclusion criteria for direct-to-treatment-phase entry: Participants who have not participated in the molecular surveillance phase but have a positive ctDNA test (conducted under other circumstances) will be considered eligible to enter to the treatment phase directly if they fulfill all the inclusion criteria listed below: 1. Signed treatment phase ICF prior to participation in any Study-related activities. 2. Male or female participants aged 18 years or older. 3. Histologically proven primary HR-positive according to the updated ASCO/CAP 2020 guidelines and HER2-negative BC as per ASCO/CAP 2018 criteria based on local testing on the most recent analyzed biopsy. 4. Availability and willingness to provide the most recently available (archival FFPE) tumor tissue sample (either from diagnostic biopsy, primary surgery, or where available from a residual disease post-neoadjuvant therapy) at the time of Study inclusion. Note I: Participants with multifocal BC may be enrolled, if archival tissue samples from at least two tumors are available and after histopathological examination, all tumors meet pathologic criteria for HR-positive and HER2-negative BC. Note II: Participants with bilateral carcinoma of the breast may be included as long as at least one of the tumors meets the criteria established by the protocol and both are HR-positive and HER2-negative tumors. 5\. Successful ctDNA assay designability, defined as the ability to generate a personalized, tumor-informed ctDNA assay based on sequencing of tumor tissue and matched germline DNA, enabling longitudinal ctDNA assessment. 6\. Confirmation of ctDNA positivity by the Study test. Note: Only participants who are confirmed as ctDNA-positive by the SignateraTM Genome test will be eligible to enter the treatment phase. External ctDNA results may be used to identify potential candidates, but eligibility will be based solely on the ctDNA status determined by the SignateraTM Genome test. 7\. Participants must have had surgery for their primary BC with documented clear margins (as per local guidelines), and they must have received radiotherapy if indicated (as per local guidelines). 8\. Fulfillment of all general treatment phase eligibility criteria listed below. 9\. No participation in another interventional clinical trial within 28 days prior to screening or concurrent participation in another interventional clinical trial. B. Inclusion criteria for all participants to treatment phase entry: Participants will be considered eligible to enter to the treatment phase if they fulfill all the eligibility criteria listed below: I. General inclusion criteria for all Study arms: 1\. Signed treatment phase ICF prior to participation in any Study treatment phase-related activities. 2\. ctDNA positivity with no evidence of locoregional or contralateral clinical or radiologic recurrence by standard assessments (breast staging scans, e.g.: mammogram, breast ultrasound, breast magnetic resonance imaging \[MRI\]). 3\. ECOG performance status 0 or 1. 4. On adjuvant treatment with ET for at least two years and no more than seven years at the time of Study enrolment with an additional three years of ET planned. Participants must have received the same ET treatment with AI or tamoxifen during at least the last six months. A temporary discontinuation of \< 90 days during the surveillance phase is allowed. 5\. Receiving LHRH agonist therapy alongside the same ET treatment for at least 90 days prior to initiation of one of the available Study treatments if male or premenopausal female participant. 6\. Prior treatment with CDK4/6i in the adjuvant setting will be allowed in the case of an interval of at least 12 months between the last CDK4/6i dose and Study inclusion in the trial. 7\. No prior treatment with SERDs will be allowed. 8. Female of reproductive potential and male participants with female partners of childbearing potential, must remain abstinent and truly abstain from sexual activity (refrains from heterosexual intercourse) or use locally recognized adequate methods of contraception (described as that with a failure rate \< 1%) for the duration of trial treatment. In addition, participants must follow these guidelines for a certain period of time after the last dose of trial treatment, specified in the protocol depending on which treatment arm the participant is allocated in. During this period of time, female and male participants must as well refrain from donating eggs or sperm. Note: Female participants will be deemed not of childbearing potential if they are postmenopausal or have had irreversible sterilization. Well-defined premenopausal status refers to women who have not reached the postmenopausal state because they are not permanently infertile due to prior bilateral oophorectomy, age ≥ 60 years or age \< 60 years with amenorrhea for ≥ 12 months and estradiol and follicle-stimulating hormone (FSH) levels in the postmenopausal range. 9\. Resolution of all acute toxic effects of prior anti-cancer therapy to Grade ≤ 1 as determined by the National Cancer Institute - Common Terminology Criteria for Adverse Events version 5.0 (NCI-CTCAE v.5.0) (except for alopecia, or other toxicities not considered a safety risk for the participant at investigator's discretion). Adverse events (AEs) of current ET treatment are not included. 10\. 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 (RBC) transfusion, and/or granulocyte colony-stimulating factor support within seven 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; Bilirubin ≤ 1.5x the upper limit of normal (ULN) (≤ 3x ULN in the case of Gilbert's disease); aspartate transaminase (AST) and alanine transaminase (ALT) ≤ 2.5x ULN; alkaline phosphatase (ALP) ≤ 2 × ULN. * Renal: serum creatinine level ≤ 1.5x the ULN or an estimated glomerular filtration rate (eGFR) ≥ 30 mL/min/1.73 m², as calculated using the 2021 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) Creatinine Equation (National Kidney Foundation \[NKF\], 2021). Note: eGFR should be determined using the recommended standardized 2021 CKD-EPI Creatine Equation (without race adjustment): eGFR (mL/min/1.73 m²) = 142 × min (Scr/κ, 1) \^α × max (Scr/κ, 1) \^-1.200 × 0.9938\^Age × 1.012 \[if female\]. Scr = serum creatinine in mg/dL, κ = 0.7 for females; 0.9 for male; α = -0.241 for females; -0.302 for males; min (Scr/κ, 1) = the lesser of Scr/κ or 1; max (Scr/κ, 1) = the greater of Scr/κ or 1; Age = age in years; The multiplication factor 1.012 is applied only for females. 11\. Participants who are able and willing to swallow, retain, and absorb oral medication. 12\. Participants must be able and willing to adhere to Study procedures. II. Additional inclusion criteria for Arm C (giredestrant + abemaciclib arm): 1. Participants with prior diagnosis of thrombosis might be included as long as they are under stable anti-coagulation regimen therapy 28 days prior to starting treatment with abemaciclib. III. Additional inclusion criteria for Arm D (giredestrant + inavolisib arm): 1\. Central confirmation of biomarker eligibility (detection of specified PIK3CA mutation(s) via Qiagen therascreen® PIK3CA RGQ PCR kit \[CE-IVD\]) in tumor tissue sample. 2\. No prior treatment with any phosphatidylinositol 3-kinase (PI3K), Akt, or mammalian target of rapamycin (mTOR) inhibitors, or any agent whose mechanism of action is to inhibit the PI3K/Akt/mTOR pathway. Exclusion criteria (treatment phase): I. General exclusion criteria: 1. Known hypersensitivity reaction to any investigational or therapeutic compound or their incorporated substances. 2. Undergoing any concurrent anti-cancer treatment for the current BC diagnosis, other than permitted adjuvant ET and/or bone-modifying agents (denosumab or bisphosphonates). 3. Major surgery (defined as requiring general anesthesia) or significant traumatic injury within 28 days of start of Study drug, or participants who have not recovered from the side effects of any major surgery. 4. Treatment with strong Cytochrome P450 3A4 (CYP3A4) inhibitors or strong CYP3A4 inducers within 14 days or five drug-elimination half-lives, whichever is longer, prior to initiation of Study treatment. 5. Active cardiac disease or history of cardiac dysfunction including any of the following: a. History (within two years from screening) or presence of idiopathic bradycardia or resting heart rate \< 50 beats per minute at screening. b. History of angina pectoris or symptomatic coronary heart disease within 12 months prior to Study entry. c. QTcF \> 450 ms for women and \> 470 ms for men by at least 3 ECGs \> 30 minutes apart. d. History or presence of an abnormal ECG that is clinically significant in the investigator's opinion, e. History of ventricular dysrhythmias or risk factors for ventricular dysrhythmias such as structural heart disease (e.g. severe left ventricular systolic dysfunction, left ventricular hypertrophy cardiomyopathy, infiltrative cardiomyopathy, moderate-to-severe valve disease), coronary heart disease (symptomatic or with ischemia demonstrated by diagnostic testing), clinically significant electrolyte abnormalities (e.g. hypokalemia, hypomagnesemia, hypocalcemia), or family history of long QT syndrome within 12 months. 6. History of pneumonitis, ILD, or pulmonary fibrosis. 7. Known history of HIV infection. 8. Clinically significant liver disease consistent with Child-Pugh C, including current known infection with HBV or HCV, current alcohol abuse, or cirrhosis. Participants with past HBV infection or resolved HBV infection (defined as having a negative HBsAg test and a positive HBcAb test, accompanied by a negative HBV DNA test) are eligible. Participants positive for HCV antibody are eligible only if PCR is negative for HCV RNA. 9. Diagnosis of an alternative cancer in the five years prior to primary BC diagnosis, other than for non-melanoma carcinoma of the skin or cervical carcinoma in situ. Other stage I tumors will be discussed case by case prior to inclusion with the Medical Monitor of the Study. 10. Females who are known to be breastfeeding or pregnant as determined by a serum pregnancy test (β-HCG) prior to the administration of any trial treatment (once during the treatment phase). 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). 11. Participant who has any other concurrent severe and/or uncontrolled medical condition that would, in the Investigator' opinion cause unacceptable safety risks, contraindicate participation in the clinical trial or compromise compliance with the protocol. 12. Participant has a history of non-compliance to medical regimen. II. Additional exclusion criteria for Arm D (giredestrant + inavolisib): 1\. Type 2 diabetes requiring ongoing systemic treatment at the time of Study entry; or any history of Type 1 diabetes. 2\. Fasting glucose ≥ 126 mg/dL or ≥ 7.0 mmol/L and hemoglobin A1c (HbA1c) ≥ 6.0%. 3\. Any concurrent ocular or intraocular condition excluding cataracts (e.g. diabetic retinopathy) that, in the opinion of the investigator, would require medical or surgical intervention during the Study period to prevent or treat vision loss that might result from that condition. 4\. Active inflammatory (e.g. uveitis or vitritis) or severe infectious conditions (e.g. keratitis, scleritis, or endophtalmitis) in either eye or history of idiopathic or autoimmune-associated uveitis in either eye.