Des-acyl ghrelin is the unacylated form of the well-characterized appetite-stimulating hormone ghrelin. It affects a number of physiological processes, including increasing adipose lipid accumulation and inhibiting adipose tissue inflammation. Breast adipose tissue inflammation in obesity is associated with an increase in the expression of the estrogen biosynthetic enzyme, aromatase, and is hypothesized to create a hormonal milieu conducive to tumour growth. We previously reported that des-acyl ghrelin inhibits the expression and activity of aromatase in isolated human adipose stromal cells (ASCs), the main site of aromatase expression in the adipose tissue. The current study aimed to examine the effect of des-acyl ghrelin on the capacity of macrophages to stimulate aromatase expression in primary human breast ASCs and effects breast tumour growth in vitro and in vivo. Results demonstrate that, in addition to direct effects on aromatase expression, des-acyl ghrelin inhibits the capacity of macrophages to stimulate aromatase. Moreover, des-acyl ghrelin also inhibits the growth of multiple breast cancer cell lines, in vitro and in vivo, independent of effects on estrogen production. Overall, these studies provide a novel mechanism for potential effects of des-acyl ghrelin to break the linkage between obesity and breast cancer.