Treatments that stimulate the immune system to attack tumours have revolutionised the treatment of some cancer types. However, these treatments have not yet been used effectively in breast cancer. More than three quarters of women with breast cancer present with the hormone-sensitive form of the disease and are subsequently treated with anti-oestrogen therapy. We have previously shown that treatment with anti-oestrogen drugs leads to infiltration of immune cells into breast tumours. We plan to investigate whether using either of two different immunotherapies in conjunction with anti-oestrogen therapies can stimulate an immune response directed against the tumour. This work will help assess whether these therapies are appropriate for treating oestrogen receptor positive tumours and, if so, whether they should be administered at the same time or separately.