Adipocytes account for the largest proportion among the cells that comprise 
breast tissue; therefore, they are considered to be a critical cell type in the 
tumor microenvironment of breast cancer. In breast cancer, adipocytes are not 
only found adjacent to cancer cells, but they also play an active role in the 
entire process of cancer development, progression, metastasis, and treatment 
response. Factors including the secretion of adipokines such as leptin and 
adiponectin, as well as autotaxin, interleukin 6, tumor necrosis factor alpha, 
and hepatic growth factor, metabolic remodeling that supports the growth of 
breast cancer by transfer of fatty acids to increase mitochondrial β-oxidation, 
extracellular matrix remodeling and endotrophin production from type IV 
collagen, and cancer-associated fibroblast phenotype changes have all been 
implicated in this comprehensive process. Moreover, adipocytes may act as 
obstacles to therapy, as they are involved in mechanisms of resistance against 
various breast cancer treatments. Adipose tissues may also be a reservoir for 
dormant tumor cells during postsurgical autologous fat grafting. Thus, 
adipocytes, and the processes and pathways in which they are involved, could be 
effective therapeutic targets for breast cancer. In this review, we focus on the 
current understanding of adipocyte biology as it affects breast cancer.