A Study to Assess the Ability of a Novel Endocrine Treatment for Breast Cancer, Irosustat, to Slow Down Cancer Growth

Objectives Primary: To assess changes in \[18F\] fluorothymidine (FLT) uptake using Positron Emission Tomography (PET) following 2 weeks of Irosustat treatment in patients with early, treatment naïve, oestrogen receptor positive (ER +ve) breast cancer Secondary: To assess the: 1. Pharmacodynamic profile of Irosustat 2. Safety and tolerability of Irosustat Study Population: Postmenopausal women with early, treatment naïve, ER +ve breast cancer