Irosustat

70% of breast cancers that occur in postmenopausal women rely on the hormone oestrogen to grow and are likely to respond to hormone treatment. This type of treatment reduces the amount of oestrogen in the body, slowing the growth of cancer or stopping it altogether. One type of hormone treatment, aromatase inhibitors (AIs), works by stopping the body from making oestrogen. Currently, women with locally advanced or metastatic breast cancer that is not being controlled by one class of AI are switched to the other class of AI. The reason for this is that some cancer cells can become resistant to one class but are still sensitive to the other class. However, oestrogen can be made in the body by two pathways and AIs block only one of these pathways. A new drug called Irosustat can reduce the production of oestrogen in the body by blocking the second pathway. This study is investigating whether adding Irosustat to AI treatment i.e. blocking both pathways at the same time, can further reduce the amount of oestrogen in the body and therefore control the breast cancer better.
27 postmenopausal women with oestrogen receptor positive locally advanced or metastatic breast cancer that is not being controlled by their current AI treatment will be recruited in this study from 9 United Kingdom (UK) hospitals. Eligible patients will receive 40mg of Irosustat once daily in addition to the AI on which they progressed. Patients will receive Irosustat for as long as it controls their cancer or until they have side effects that stop them from taking treatment. Patients will be seen monthly for the first 6 months and every 3 months thereafter. Participating patients will also be given the option to take part in the exploratory part of this study by donating tissue and blood samples.