CXCR4 and posterior cortical atrophy: Focusing on PCa bone metastasis, which occurs in the majority of CRPCs and always develops resistance to chemotherapy, here we report a mechanism for the development of chemoresistant bone metastasis in PCa progression, i.e., heavy acetylation of the KLF5 transcription factor in the bone microenvironment causes bone metastatic lesions by activating the CXCL12/CXCR4 chemokine axis and other paracrine signaling pathways such as those of IL-11 and SHH (Fig. 9e).