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

Irosustat will be administered once daily in 40mg tablets. Treatment will start the day after the baseline FLT-PET and will be continued for a minimum of 2 weeks until the follow up FLT PET scan. For those patients who have consented to a repeat tumour biopsy, treatment will be extended to the day before the procedure. Study medication should be taken in the morning under fasting conditions with a glass of water, 30 minutes before breakfast.