CA6 and breast cancer: Through upregulating the PMN-related genes in lung epithelial cells, regulating lung fibroblasts to induce ECM deposition, and inhibiting the PTEN/CCL2/VEGF-A signaling pathway of lung macrophages to affect M2-type polarization and angiogenesis, Cav-I in BC-derived exosomes promotes PMN formation and BC lung metastasis.