ESR1 and breast cancer: Wu et al. [8] found that exosomal miR‐19a derived from estrogen receptor-positive breast cancer cells promoted osteoclast differentiation and bone metastasis, because miR-19a inhibits the expression of PTEN, thereby activating the NF-κB and AKT pathways in osteoclasts, which would create a microenvironment favorable for colonization in the bone [8].