When fat becomes an ally of the enemy: adipose tissue as collaborator in human breast cancer.

Since the discovery of leptin in 1994, our vision of adipose tissue as a static organ regulating mainly lipid storage and release has been completely overthrown, and adipose tissue is now seen as an active and integral organ in human physiology. In the past years, extensive research has tremendously given us more insights in the mechanisms and pathways involved not only in normal but also in 'sick' adipose tissue, for example, in obesity and lipodystrophy. With growing evidence of a link between obesity and several types of cancer, research focusing on the interaction between adipose tissue and cancer has begun to unravel the interesting but complex multi-lateral communication between the different players. With breast cancer as one of the first cancer types where a positive correlation between obesity and breast cancer incidence and prognosis in post-menopausal women was found, we have focused this review on the paracrine and endocrine role of adipose tissue in breast cancer initiation and progression. As important inter-species differences in adipose tissue occur, we mainly selected human adipose tissue- and breast cancer-based studies with a short reflection on therapeutic possibilities. This review is part of the special issue on "Adiposopathy in Cancer and (Cardio)Metabolic Diseases".