Furthermore, exosomes obtained from estrogen receptor (ER)-positive breast cancer cells were observed to transfer miR-19a to osteoclast precursors, which promoted osteoclast differentiation by reducing the expression of phosphatase and tensin homolog (PTEN), thereby activating the nuclear factor-kappa B (NF-κB) and protein kinase B (AKT) signaling pathways [8]. Here, PTEN is linked to breast cancer.