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

This study is investigating the effects of a new hormone treatment for breast cancer called Irosustat. Seventy percent of breast cancers in post-menopausal wome rely on oestrogen to grow therefore are likely to respond to hormone therapy. Irosustat blocks a different pathway of steroid synthesis to Aromatase, reducing in this way oestrogen levels in the body. As less oestrogen reaches the breast cancer, it grows more slowly or stops growing altogether. IPET will recruit postmenopausal women with early, hormone sensitive, treatment naive breast cancer will receive 40mg of Irosustat once daily for 2 weeks. The effects of Irosustat on breast cancer will be evaluated by PET scans (Positron Emission Tomography) using a radioactive substance called FLT as a tracer. The scans will be performed in a PET-CT scanner which combines a PET scan and a CT scan (Computer Tomography) into one scan. This type of scan can show how body tissues are working, as well as what they look like. FLT-PET scans will be performed before and following treatment with Irosustat. As cancer cells grow faster than the normal cells around them, they will take up more of the radioactive substance, and so stand out clearly on the scan. If Irosustat is slowing down the cancer growth, the cancer will take up less of the tracer. Blood samples will be taken at regular intervals to assess what the new drug does to the body and the safety and tolerability of Irosustat will be assessed. The study incorporates translation aspects/endpoints which are based on the collection of tumour biopsies before and after treatment with Irosustat although the later biopsy is not mandatory.