Cancer-associated fibroblasts support bone tropic metastasis by acting as coordinators between the tumor microenvironment and bone matrix in breast cancer.

Bone is a common site of metastasis for various types of cancer cells, including breast cancer, and the consequent skeleton-related events observed in patients are severe and often fatal. Currently, it is widely accepted that cancer-associated fibroblasts (CAFs) confer a metastasis-promoting property to breast cancer cells. Furthermore, clinical observations suggest that CAFs mediate the bone tropism of metastatic breast cancer cells. Therefore, a deeper understanding of the mechanism by which CAFs are involved in the bone-tropic metastasis of breast cancer can facilitate the study of the novel and effective therapeutic drugs for the corresponding targets. In this review, we focused on the coordinator role of CAFs in remolding breast cancer cells and remodeling the bone marrow during metastasis. We discussed the potential roles of the CXCL12/CXCR4 axis, the CAFs-CSCs reinforcing loop, and exosomes in this malignant process. In summary, in agreement with Paget's theory, CAFs play a pivotal role in bone colonization by breast cancer cells by providing a "fertile soil" for the "selected seeds" by influencing tumor-intrinsic characteristics and microenvironment (ME).