The fundamental role of the mammary gland is to produce milk to feed young. Considering this is only required for a certain length of time, the mammary gland must undergo substantial preparatory remodelling during pregnancy, and, similarly, the architecture of the gland must be restored to its pre-pregnant state when milk production is no longer required. This post-lactation regression of the mammary gland (Involution) has a distinct inflammatory signature, whereby immune cells are recruited to the gland to assist with the remodelling process. I am an immunologist and I am interested in how this post-pregnancy inflammation of the mammary gland can be tumourigenic. I am particularly interested in how this process is exacerbated in older first-time mothers, as this may be of great importance in today’s society, where starting a family is often delayed.