In the bone marrow stroma, M2-polarized macrophages have been shown to maintain prolonged dormancy of breast cancer cells through gap junctional intercellular communication, whereas M1-polarized macrophages have been reported to reverse tumor cell dormancy via exosome-mediated activation of the NF-κB signaling pathway.110 In pulmonary metastatic lesions of breast cancer, alveolar macrophages sustain the dormant state of disseminated cancer cells through TGF-β2 signaling, effectively suppressing pulmonary metastasis. Here, TGFB2 is linked to breast cancer.