Cancer metastasis is the leading cause of mortality among breast cancer patients. Type 2 diabetes mellitus (T2DM) has been suggested as a risk factor of breast cancer; however, whether or not T2DM is associated with breast tumor metastasis remains unclear. In the present study, we examined the involvement of T2DM with breast cancer metastasis by a combined approach of a meta-analysis and experimental research. The results of a systematic review and meta-analysis suggested that diabetes significantly increases the risk of lymph node metastasis by 1.10-fold (P<0.01). Consistently, our data from experimental research showed that T2DM induced paracrine effects of mesenchymal stem cell (MSCs), a key contributor to cancer progression, to stimulate metastasis of breast cancer cells (BCCs) by two independent mechanisms. First, T2DM induced the excess secretion of IL6 from MSCs, which activated the JAK/STAT3 pathway in BCCs, thus promoting the metastasis of BCCs. Second, beside the EGR-1/IL6-dependent mechanism, T2DM altered the functions of MSC-derived extracellular vesicles (EVs) which are highly associated with the metastasis of BCCs. Our present study showed that T2DM is a risk factor for breast cancer metastasis, and MSC-derived EVs might be useful for developing a novel anti-breast cancer therapy strategy.