A Study to Investigate the Biological Effects of AZD9833 in Women With ER-positive, HER2 Negative Primary Breast Cancer

The study will be conducted in approximately 20 study centers across 3 countries and will be conducted in three stages (stage 1, stage 2 and stage 3). After the screening visit and confirmation of eligibility, evaluable participants will be enrolled across treatment groups. In stage 1, up to 24 evaluable participants across two treatment groups will be enrolled. A Safety and Data Monitoring Committee will convene to review stage 1 data and decide whether further treatment groups are required in stage 2. Stage 2 will include participants across up to 3 treatment groups. Stage 3 will include two treatment groups:

Stage 1 Group 1: AZD9833 Dose A once daily Group 2: AZD9833 Dose B once daily

Stage 2 Group 1: AZD9833 Dose A once daily Group 2: AZD9833 Dose B once daily Group 3: AZD9833 Dose C once daily

Stage 3 Group 1: AZD9833 Dose A once daily Group 2: AZD9833 Dose B once daily

Adverse events and concomitant medications information will be collected throughout the study. Thereafter there will be 28-day follow-up visit after discontinuation of study treatment

Inclusion criteria

• Provision of written informed consent prior to study entry
• Female participants aged at least 18 years
• Post-menopausal status defined as meeting at least one of the following criteria:

• Have undergone a bilateral oophorectomy
• Age ≥ 60 years
• Age ≥ 50 and < 60 years and with cessation of menses ≥ 12 months and follicle-stimulating hormone and oestradiol levels in the post-menopausal range and with an intact uterus in the absence of oral contraception or hormone replacement therapy prior to the diagnosis of breast cancer
• Female participants with newly diagnosed primary breast cancer scheduled to undergo treatment with curative intent by surgery and irrespective of clinical node status
• Histologically confirmed invasive breast cancer involving a palpable tumour of any size, or a tumour with an ultrasound assessed diameter of ≥ 1.0 cm
• Participants with adequately treated non-melanoma skin cancer, curatively treated in-situ cancer of the cervix, or other solid tumours curatively treated with no evidence of disease for ≥ 3 months can be considered for the study
• According to the local laboratory participants must have:

• ER positive breast cancer
• HER2-negative breast cancer
• Eastern Cooperative Oncology Group (ECOG) performance status 0 to 1

Exclusion criteria

• Previous systemic or local treatment for the new primary breast cancer currently under investigation (including surgery, radiotherapy, cytotoxic and endocrine treatments)
• Intervention with any of the following:

• Use of sex-hormone-containing drugs within 6 months prior to the first dose of study treatment
• Medications or herbal supplements known to be strong inhibitors/inducers of CYP3A4/5, sensitive CYP2B6 substrates and drugs which are substrates of CYP2C9 and/or CYP2C19 which have a narrow therapeutic index
• Drugs that are known to prolong QT and have a known risk of torsades de pointes
• Inflammatory breast cancer
• Any evidence of severe or uncontrolled systemic diseases which in the investigator's opinion makes it undesirable for the participant to participate in the study
• Any of the following cardiovascular criteria: Mean resting QTcF > 470 msec; resting heart rate of < 50 bpm for stages 1 and 2 at screening;resting heart rate <60 bpm at screening for Stage 3; any clinically important abnormalities in rhythm, conduction, or morphology of resting ECG; any factors that increase the risk of QTc prolongation or risk of arrhythmic events; known left ventricular ejection fraction < 50%; significant cardiovascular procedure or event within the last 6 months; uncontrolled hypertension or symptomatic hypotension
• Inadequate bone marrow reserve or organ function
• Refractory nausea and vomiting, uncontrolled chronic gastrointestinal diseases, inability to swallow the formulated product, or previous significant bowel resection that would preclude adequate absorption of AZD9833
• History of hypersensitivity to active or inactive excipients of AZD9833
• Previous randomisation in the present study
• Judgement 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