Adipocyte-derived exosomes may promote breast cancer progression in type 2 diabetes.

Obesity and metabolic diseases, such as insulin resistance and type 2 diabetes (T2D), are associated with metastatic breast cancer in postmenopausal women. Here, we investigated the critical cellular and molecular factors behind this link. We found that primary human adipocytes shed extracellular vesicles, specifically exosomes, that induced the expression of genes associated with epithelial-to-mesenchymal transition (EMT) and cancer stem–like cell (CSC) traits in cocultured breast cancer cell lines. Transcription of these genes was further increased in cells exposed to exosomes shed from T2D patient–derived adipocytes or insulin-resistant adipocytes and required the epigenetic reader proteins BRD2 and BRD4 in recipient cells. The thrombospondin family protein TSP5, which is associated with cancer, was more abundant in exosomes from T2D or insulin-resistant adipocytes and partially contributed to EMT in recipient cells. Bioinformatic analysis of breast cancer patient tissue showed that greater coexpression of COMP (which encodes TSP5) and BRD2 or BRD3 correlated with poorer prognosis, specifically decreased distant metastasis–free survival. Our findings reveal a mechanism of exosome-mediated cross-talk between metabolically abnormal adipocytes and breast cancer cells that may promote tumor aggressiveness in patients with T2D.