Stromal-derived exosomes promote the evolution of hormonal therapy–resistant cancer stem-like cells (CSC). In tumor-stroma niches of breast cancer, IL6 from cancer-associated fibroblasts (CAF) increases the biogenesis of miRNAs high exosomes, facilitating the transfer of genetic material from the stroma to tumor cells and the conversion of non-CSCs into CSCs. Using immunohistochemical analysis for pan-cytokeratin, we detected the presence of single breast cancer cell clusters surrounded by noncancer cells in human breast cancer xenografts from the coinjection of IL6 high CAFs with ER⁺ breast cancer cells. For details, see article by Sansone and colleagues on page 1927.