Osteocytes in the Metastatic Bone Niche: Mechanistic Pathways and Therapeutic Targets

Osteocytes, once viewed mainly as passive bone-embedded cells, are now recognized as active regulators of the metastatic bone niche. Emerging evidence indicates that these cells integrate mechanical, inflammatory, and tumor-derived cues to influence metastatic seeding, dormancy, reactivation, and lesion progression in bone. This review synthesizes current understanding of osteocyte contributions to skeletal metastasis. We discuss core signaling axes, including osteocyte-derived RANKL/OPG balance, Wnt antagonists (sclerostin/DKK1), mechanotransduction pathways (Piezo1 signaling and connexin-43 hemichannels), and osteocyte paracrine mediators (extracellular vesicles and senescence-associated factors), and examine how each axis modulates tumor cell dormancy, osteolysis, or osteoblastic progression. We then review translational strategies targeting osteocytes, recent preclinical and clinical insights. Emerging biomarkers (e.g., serum sclerostin, DKK1, bone turnover markers) and immune-skeletal imaging approaches are also considered. Controversies, including the paradoxical effects of sclerostin blockade and the identity of in vivo RANKL sources, are discussed. Finally, we outline key knowledge gaps and propose endpoints for future trials. In summary, an osteocyte-centric perspective reveals novel targets and strategies for managing bone metastases, guiding future translational research.