Expression of the zinc-finger transcription factor Osterix (SP7) in invasive breast cancer and its prognostic significance.

INTRODUCTION: Osterix, encoded by SP7, is a transcription factor crucial in osteoblast differentiation and bone formation. While initially characterised in bone development, emerging evidence suggests its involvement in cancer, particularly breast cancer metastasis to bone. METHODS: Osterix protein expression was evaluated in 1340 early-stage invasive breast tumours by immunohistochemistry. Cytoplasmic and nuclear expression levels were assessed and associations with clinicopathological variables and patient survival determined. Additionally, SP7 mRNA expression was examined in the METABRIC cohort of patients. Gene set enrichment analysis (GSEA) was performed to explore the role of osterix in the hallmarks of cancer genesets. RESULTS: Results revealed significant associations between reduced nuclear osterix protein expression and adverse clinicopathological features, including larger tumour size, higher grade, and poor Nottingham Prognostic Index. Low nuclear osterix protein expression was also linked to shorter breast cancer-specific survival and distant metastasis free survival, particularly in patients with HER2 positive tumours. No associations were found between SP7 mRNA expression and clinicopathological variables or survival outcomes. GSEA identified enrichment of genes involved in KRAS signaling in tumours with high SP7 expression. CONCLUSION: These data suggest that reduced nuclear expression of osterix is associated with poor clinical outcome of breast cancer patients and may be of clinical relevance.