Shelby J. Colvin

Background: Lung cancer is the leading cause of cancer-related mortality worldwide, and 30–60% of patients with metastatic non-small cell lung cancer (NSCLC) develop bone metastases, most of which are osteolytic.^1,2 Osteolytic lesions result from excessive osteoclast-mediated bone resorption, and their clinical consequences—pathologic fractures, spinal cord compression, severe bone pain, and hypercalcemia—substantially diminish quality of life and portend poor prognosis.² Current therapies, including bisphosphonates and RANKL-targeting agents such as denosumab, provide only partial relief.¹ The molecular mechanisms underlying pre-metastatic niche establishment, osteoclast hyperactivation, and the self-reinforcing “vicious cycle” between tumor cells and bone remain incompletely understood, limiting the development of targeted therapies and diagnostic tools.

Objective: This narrative review aimed to synthesize current evidence on the molecular mediators driving osteolytic bone metastasis in lung cancer, focusing on pre-metastatic niche formation, RANKL-dependent and RANKL-independent osteoclastogenic signaling, and bone-derived feedback signals that promote tumor proliferation.

Search Methods: A literature search was conducted in PubMed from 2017 to 2024 using the following MeSH terms and keywords: “lung cancer,” “bone metastasis,” “osteolytic lesion,” “osteoclast,” “RANKL,” “extracellular vesicles,” “KRAS,” “HOXC10,” and “vicious cycle.”

Results: Six primary studies were reviewed. Qiu et al. (2024) showed that lung adenocarcinoma cells secrete ITGB3-enriched extracellular vesicles (EVs) that prime the bone microenvironment prior to tumor arrival by suppressing p38 MAPK signaling in osteoclast precursors, with elevated serum EV-ITGB3 proposed as a liquid biopsy biomarker.³ Brouns et al. (2023) demonstrated in 73 metastatic NSCLC patients that elevated tumor RANKL expression and increased RANKL:OPG ratios were significantly associated with skeletal metastasis risk (p = 0.002), particularly in KRAS-mutant patients.¹ Chen et al. (2023) identified bone sialoprotein (BSP) as a critical amplifier of RANKL-dependent osteoclastogenesis via the PI3K/AKT/AP-1/MMP14 axis; BSP knockdown significantly reduced osteolytic lesion formation in murine models.² He et al. (2022) established an IL-19/IL-20RB/STAT3 bone-to-tumor feedback axis in which osteoclast-secreted IL-19 drives tumor proliferation; IL-20RB knockdown reduced bone tumor burden 10–100-fold in murine models.⁴ Li et al. (2024) identified HOXC10 as a RANKL-independent driver of osteoclastogenesis in KRAS-mutant lung cancer via the NOD1/MAPK-ERK pathway, with HOXC10 knockdown reducing osteoclast formation by 55–65% and tumor growth by 53–85% preclinically.⁵ Zhao et al. (2023) further characterized a miR-182/IL-8/STAT3 axis promoting RANKL-independent osteolysis, with IL-8-neutralizing antibodies inhibiting osteolytic metastasis in murine models.⁶

Conclusion: Osteolytic bone metastasis in lung cancer involves a multi-step vicious cycle encompassing EV-mediated pre-metastatic niche formation, convergent RANKL-dependent and RANKL-independent osteoclastogenic pathways, and osteoclast-derived tumor growth signals. Several mediators—including EV-ITGB3, RANKL:OPG ratios, BSP, HOXC10, IL-20RB, and IL-8—represent promising biomarkers and therapeutic targets. The molecular redundancy across these pathways suggests that combination strategies targeting multiple nodes of the cycle will be necessary for meaningful clinical benefit. Future work should focus on translating these preclinical findings into clinical trials and exploring interactions between osteolytic signaling and emerging immunotherapies in metastatic lung cancer.

Works Cited

1. Brouns AJWM, Derks JL, Paats MS, et al. Association of RANKL and EGFR gene expression with bone metastases in patients with metastatic non–small cell lung cancer. Front Oncol. 2023;13:1145001. doi:10.3389/fonc.2023.1145001
2. Chen WC, et al. Bone sialoprotein promotes lung cancer osteolytic bone metastasis via MMP14-dependent mechanisms. Biochem Pharmacol. 2023;211:115529. doi:10.1016/j.bcp.2023.115529
3. Qiu R, Deng Y, Lu Y, Liu X, Huang Q, Du Y. ITGB3-enriched extracellular vesicles mediate the formation of osteoclastic pre-metastatic niche to promote lung adenocarcinoma bone metastasis. Mol Carcinog. 2024;63:2190-2204. doi:10.1002/mc.23803
4. He Y, Luo W, Liu Y, et al. IL-20RB mediates tumoral response to osteoclastic niches and promotes bone metastasis of lung cancer. J Clin Invest. 2022;132(20):e157917. doi:10.1172/JCI157917
5. Li K, Yang B, Du Y, et al. The HOXC10/NOD1/ERK axis drives osteolytic bone metastasis of pan-KRAS-mutant lung cancer. Bone Res. 2024;12:47. doi:10.1038/s41413-024-00350-8
6. Zhao MN, Zhang LF, Sun Z, et al. A novel microRNA-182/Interleukin-8 regulatory axis controls osteolytic bone metastasis of lung cancer. Cell Death Dis. 2023;14:298. doi:10.1038/s41419-023-05819-8