Comparing ARomatase Inhibition when given with or without SaracaTinib as an Advanced breast CAncer Therapy (ARISTACAT)

INTERVENTION: The patients will be allocated to a treatment using a minimisation algorithm. Stratification factors will be: 1. AI sensitivity strata 2. Disease site (bone metastases alone versus any other sites 3. Bisphosphonate use 4. Performance status (0 v 1 v 2) 5. Treatment centre Patients will be enrolled into one of two strata: 1. AI‐sensitive/ naïve These patients with have potentially AI‐sensitive tumours Treatment = anastrazole 1mg daily + saracatinib 175 mg daily OR exemestane 25mg daily + saracatinib 175 mg daily 2. Prior‐AI These patients will have cancers which have already progressed on an AI, but for whom there is likely to still be some endocrine sensitivity Treatment = anastrazole 1mg daily + placebo daily OR exemestane 25mg daily + placebo daily Saracatinib (AZD0530) is an oral src inhibitor and can be administered with or without food. The choice of either anastrazole or exemestane is driven by what would be an acceptable standard therapy for the patient, and then the patients are randomised to either get saracatinib or placebo. CONDITION: Advanced Breast Cancer ; Cancer ; Malignant neoplasm of breast PRIMARY OUTCOME: 1. Progression free survival; 2. Time to progression will be measured through standard, regular, clinical assessment SECONDARY OUTCOME: 1. Toxicity; 2. Change in tumour size analysed using a Waterfall plot in the two strata separately; 3. Overall survival INCLUSION CRITERIA: 1. Females who are clearly post menopausal with Estrogen Receptor (ER) positive (Allred score = 3) advanced breast cancer with at least one lesion which is measurable. They may also have additional evaluable but non‐measurable lesions. 2. Patients must be performance status 0 ? 2 3. Suitable for treatment with an aromatase inhibitor 4. Life expectancy > 3 months 5. Cancer must be HER2‐ (by FISH and/or IHC as appropriate), OR if the cancer is HER2+ the patient must not be a candidate for ant‐HER2 therapy 6. All patients will need to also meet inclusion criteria for one of the two main strata: 6.1. ?AI‐sensitive/naive? group ? either never previously treated with an aromatase inhibitor, but if treated with tamoxifen must not have rapid progression on tamoxifen (i.e. treated for at least 24 months adjuvant or = 6 months in metastatic setting); or, if previously treated with an AI, only in the adjuvant or neo‐adjuvant setting AND have remained free of