This study aimed to identify precise biomarkers for breast cancer bone metastasis (BCa-BM) using a comprehensive bioinformatics approach. Utilizing five datasets from the Gene Expression Omnibus (GEO) (39), comprising 232 BCa tumor samples and 84 BM metastatic tumor samples, the analysis identified 90 common differentially expressed genes (DEGs). Among these, 28 were down-regulated and 62 were up-regulated in BM samples compared to BCa samples. Notably, 18 genes exhibited significant interactions within a protein-protein interaction (PPI) network constructed using STRING (40), highlighting their central roles in BCa-BM progression. The identification of hub genes such as RACGAP1, PPP1CC, RAD23A, PSMD1, and RPL26L1 underscores their potential significance in BCa metastasis to bone. These genes, validated through topological analysis in Cytoscape 3.9.1 (41), are implicated in critical biological processes like cell growth, skeletal muscle development, and cell communication. Importantly, RPL26L1 emerged as a standout biomarker with upregulation in BCa-BM samples correlating significantly with worse overall survival, as validated by TCGA data.
Survival analysis using GEPIA2 and TCGA(42) data further supported the prognostic relevance of these biomarkers, particularly highlighting RPL26L1, PSMD1, and RAD23A for their association with poorer disease-free survival outcomes. Literature review also substantiated RACGAP1, PPP1CC, and RAD23A as potential diagnostic biomarkers in cancer progression, including breast cancer bone metastasis, reinforcing their roles in metastatic processes (43–46). GTPase-activating protein (GAP) is encoded by the protein-coding gene RACGAP1 (Rac GTPase-activating protein 1). According to Zhou et al. (2021), there was a high expression of RACGAP in breast cancer, which was linked to poor overall survival and several subtypes of the disease (43). Numerous cellular processes, including as cytokinesis, transformation, invasive migration, and metastasis, have been linked to the vital protein RACGAP1. Numerous investigations have examined RACGAP1's function in various human cancer types (44). Belonging to the Serine/threonine-protein phosphatase family, protein phosphatase-1 (PP1) is involved in several physiological processes, such as glycogen metabolism, cellular proliferation, and cell receptor modulation. Human mammary tissues express the protein phosphatase-1 catalytic units, PPP1CA, PPP1CB, and PPP1CC; elevated levels of these units represent a positive clinical signal for patient survival and a lower risk of bone metastases (45). Rad23 is involved in several key biological processes, including apoptosis, development, DNA repair, cell cycle regulation, and carcinogenesis (47). Additionally, it was discovered that the expression profiles of the metastasis-specific protein RAD23B correlated with the overall survival of invasive BC patients and were consistent with their gene expression levels in BRCA patients. These findings raise the possibility that these proteins could serve as potential exosome markers for BC metastasis (46).
Functional enrichment and pathway analyses revealed that these DEGs are predominantly involved in pathways related to cell cycle regulation, skeletal muscle development, and cell communication. Disruptions in these pathways may facilitate the metastatic cascade, providing potential targets for therapeutic interventions aimed at delaying or preventing bone metastasis in breast cancer (48).
The identification of precise biomarkers such as RACGAP1, PPP1CC, RAD23A, PSMD1, and particularly RPL26L1, offers significant clinical implications. These biomarkers can potentially enhance the accuracy of prognostic models, guiding personalized treatment strategies for breast cancer patients at risk of bone metastasis. Early intervention targeting these biomarkers could improve patient outcomes by mitigating the progression of metastasis.
The integration of bioinformatics tools and comprehensive datasets from GEO and TCGA underscores the robustness of the findings (49). However, the reliance on gene expression data necessitates further experimental validation to elucidate the functional roles of these biomarkers in vivo and to explore their potential as therapeutic targets (50).
Despite its strengths, this study is limited by its reliance on retrospective data analysis and bioinformatics predictions. The findings require validation through experimental studies to confirm the functional roles of identified biomarkers in BCa-BM progression. Additionally, the study's focus on a subset of DEGs may overlook other relevant genes and pathways contributing to metastasis.
Future research should consider expanding the analysis to include broader genomic and clinical data sets, as well as experimental validation in preclinical models and clinical samples. Such efforts will help translate these bioinformatics insights into clinically actionable strategies for managing breast cancer metastasis.
Future research should prioritize experimental validation of RACGAP1, PPP1CC, RAD23A, PSMD1, and RPL26L1 using cell culture models and animal studies. Investigating the molecular mechanisms underlying their roles in BCa-BM progression, particularly focusing on interactions within the identified pathways, will provide deeper insights into metastatic processes. Moreover, exploring targeted therapies aimed at modulating the cell cycle, skeletal muscle development, and cell communication pathways could yield novel strategies for preventing or treating bone metastasis in breast cancer patients. Integrating multi-omics approaches and functional assays will further enhance our understanding of these biomarkers' clinical relevance.
In conclusion, this study's expression-based network approach successfully prioritized precise biomarkers for breast cancer bone metastasis. The identification of hub genes and their association with clinical outcomes highlights their potential as prognostic markers and therapeutic targets. These findings pave the way for advancing personalized medicine in breast cancer management, offering hope for improved outcomes through targeted interventions aimed at mitigating bone metastasis. Further research and validation are essential to translate these discoveries into clinical practice effectively.