The role of IL-1B in breast cancer bone metastasis.

Interleukin-1B (IL-1B) is a potent pro-inflammatory cytokine that plays multiple, pivotal roles, in the complex interplay between breast cancer cells and the bone microenvironment. IL-1B is involved in the growth of the primary tumours, regulation of inflammation within the tumour microenvironment, promotion of epithelial to mesenchymal transition (EMT), migration and invasion. Moreover, when breast cancer cells arrive in the bone microenvironment there is an upregulation of IL-1B which promotes the creation of a conducive niche for metastatic breast cancer cells as well as stimulating initiation of the vicious cycle of bone metastasis. Pre-clinical studies have demonstrated that inhibition of IL-1 signalling reduces bone metastasis from oestrogen receptor positive/triple-negative breast cancers in various mouse models. However, effects on primary tumours and soft tissue metastasis remain controversial with some studies showing increased tumour growth in these sites, whilst others show no effects. Notably, combining anti-IL-1 therapy with standard-of-care treatments, such as chemotherapy and immunotherapy, has been demonstrated to reduce the growth of primary tumours, bone metastasis, as well as metastatic outgrowth in other organs. This review focuses on the mechanisms by which IL-1B promotes breast cancer bone metastasis.