BMP-2 was reported to facilitate epithelial-to-mesenchymal transition (EMT)6 and promote the motility and invasiveness of breast cancer cells in vitro and in mouse xenograft model.7,8 A recent study reported that the BMP-2 pathway can be activated by pollutants exposure, and contributes to stem cell transformation and breast cancer initiation.9 However, the mechanisms by which BMP-2 promotes EMT and breast cancer metastasis, and its relationship with BCSC development, remain largely unknown. The gene discussed is BMP2; the disease is breast cancer.