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