Effect of Capivasertib on ctDNA in ER Positive Breast Cancer

Inclusion Criteria: 1. Written informed consent prior to any study specific procedures 2. Female aged \>18 years 3. Histologically confirmed ER positive HER2 negative breast cancer 4. Post menopausal (or biochemically post-menopausal) 5. Completed standard initial treatment and established on aromatase inhibitor (AI) for \> 6 months and planned for at least 2 more years 6. Tolerating AI well 7. Eastern Cooperative Oncology Group (ECOG) performance status 0-1 (see Appendix 1) with no deterioration over the previous 2 weeks prior to baseline or day of first dosing 8. Minimum life expectancy of 12 weeks 9. Availability of tissue from diagnosis/treatment to assess ctDNA status 10. Relatively high risk for relapse (all except T1N0 or T2N0) using a risk stratified recruitment process 11. Adequate organ and bone marrow function as follows (a-c cannot be met with transfusions or growth factor support administered within 14 days of starting the first dose): 1. Haemoglobin ≥9.0 g/dL (\>5.59 mmol/L). 2. Absolute neutrophil count ≥1.0×109/L. 3. Platelet count ≥100×109/L. 4. Total bilirubin ≤1.5×the upper limit of normal (ULN) or ≤3×ULN in the presence of documented Gilbert's syndrome (unconjugated hyperbilirubinemia). 5. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≤2.5×ULN; for participants with hepatic metastases, ALT or AST ≤5×ULN.Elevated alkaline phosphatase (ALP) is not exclusionary if due to the presence of bone metastasis and liver function is otherwise considered adequate in the investigator's judgement. 6. f) Creatinine clearance (CrCL) \>50 mL/min per the Cockcroft-Gault formula (using actual body weight) without the need for chronic dialysis therapy. Exclusion Criteria: 1. Metastatic disease at screening 2. ECOG performance status \>1 (see Appendix 1) 3. History of another primary malignancy except for malignancy treated with curative intent with no known active disease ≥ 5 years before the first dose of study intervention and of low potential risk for recurrence. Exceptions include basal cell carcinoma of the skin and squamous cell carcinoma of the skin that has undergone potentially curative therapy 4. Known to have active hepatitis infection, positive hepatitis C antibody, hepatitis B virus surface antigen or hepatitis B virus core antibody, at screening. Known to have human immunodeficiency virus (HIV) with a CD4+ T-cell count \< 350 cells/uL or a history of an acquired immunodeficiency syndrome (AIDS)-defining opportunistic infection within the past 12 months. (HIV inclusion criteria may be adjusted to lower CD4+ count values if clinically indicated if the patient has a potentially curable malignancy or for interventions in a later stage of development that have demonstrated prior activity within a given cancer, please adjust if necessary.) Known to have active tuberculosis infection (clinical evaluation that may include clinical history, physical examination and radiographic findings, or tuberculosis testing in line with local practice) 5. Known history of drug or alcohol abuse within 2 years 6. History of interstitial lung disease 7. Any other disease, physical examination finding, or clinical laboratory finding that, in the investigator's opinion, gives reasonable suspicion of a disease or condition that contraindicates the use of an investigational drug, may affect the interpretation of the results, render the patient at high risk from treatment complications or interferes with obtaining informed consent 8. Clinically significant abnormalities of glucose metabolism as defined by any of the following at screening: 1. Patients with diabetes mellitus type I or diabetes mellitus type II requiring insulin treatment 2. HbA1c ≥ 8.0% (63.9 mmol/mol) 9. Prior treatment with any of the following: 1. Participation in another clinical study with an IMP administered in the last \<\<2 weeks or 5 half-lives, whichever is longer 2. AKT, PI3K and MTOR inhibitors 3. Any other chemotherapy, immunotherapy, immunosuppressant medication (other than corticosteroids) or anticancer agents (other than current endocrine therapy with AI +/- LHRH analogies) within 3 weeks of the first dose of study treatment. A longer washout may be required for drugs with a long half-life (eg biologics) as agreed with the sponsor 4. Palliative radiotherapy within 2 weeks; or radiotherapy to more than 30% of the bone marrow within 4 weeks before the first dose of study intervention 5. Major surgical procedure (excluding placement of vascular access) or significant traumatic injury within 4 weeks of the first dose of study intervention or an anticipated need for major surgery during the study 6. Potent inhibitors or inducers of CYP3A4 within 2 weeks prior to the first dose of study treatment (3 weeks for St John\'s Wort) or sensitive substrates of CYP344, CYP2C9 and/or CYP2D6 with a narrow therapeutic window within 1 week prior to the first study dose 10. Currently pregnant or breast feeding 11. As judged by the investigator, any evidence of diseases (such as severe or uncontrolled systemic diseases, including uncontrolled hypertension, renal transplant and active bleeding diseases which, in the investigator's opinion, makes it undesirable for the participant to participate in the study or that would jeopardise compliance with the protocol 12. Judgment by the investigator that the participant should not participate in the study if the participant is unlikely to comply with study procedures, restrictions and requirements 13. Participants with a known hypersensitivity to Capivasertib or any of the excipients of the product 14. Refractory nausea and vomiting, chronic gastrointestinal disease, inability to swallow the formulated product, or previous significant bowel resection that would preclude adequate absorption, distribution, metabolism, or excretion of Capivasertib 15. Persistent toxicities (CTCAE Grade ≥2) caused by previous anticancer therapy, excluding alopecia. Participants with irreversible toxicity that is not reasonably expected to be exacerbated by study intervention may be included (e.g. hearing loss) 16. Investigator judgment of 1 or more of the following: 17. Mean resting corrected QT interval \>470 ms, obtained from ECG performed at screening. 18. Medical history significant for arrhythmia (e.g., multifocal premature ventricular contractions, bigeminy, trigeminy, ventricular tachycardia), which is symptomatic or requires treatment (CTCAE Grade 3), symptomatic or uncontrolled atrial fibrillation despite treatment, or asymptomatic sustained ventricular tachycardia. Participants with atrial fibrillation controlled by medication or arrhythmias controlled by pacemakers may be permitted to enter the study. 19. Any factors that increase the risk of QTc prolongation or risk of arrhythmic events such as heart failure, hypokalaemia of Grade ≥1, potential for Torsades de Pointes, congenital long QT syndrome, family history of long QT syndrome or unexplained sudden death under 40 years of age in first-degree relative, history of QT prolongation associated with other medications that required discontinuation of the medication (see section 6.5 for guidance on participants receiving any concomitant medication known to prolong the QT interval). 20. Experience of any of the following procedures or conditions in the preceding 6 months: coronary artery bypass graft, angioplasty, vascular stent, myocardial infarction, angina pectoris, congestive heart failure New York Heart Association (NYHA) grade ≥2. 21. Uncontrolled hypotension: systolic blood pressure \<90 mmHg and/or diastolic blood pressure \<50 mmHg. 22. Involvement in the planning and/or conduct of the study (applies to both Investigator staff and/or staff at the study site) 23. Previous enrolment in the study