Abstract

Background Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype associated with high rates of recurrence, metastasis, and poor prognosis. Identifying key molecular regulators is essential for improving prognostic assessment and therapeutic strategies in TNBC. However, the expression pattern, clinical significance, and underlying regulatory mechanisms of SAM pointed domain-containing ETS transcription factor (SPDEF) in TNBC remain unclear. This study aims to investigate the expression pattern, clinical significance, and underlying regulatory mechanisms of SPDEF in regulating tumor cell biological behaviors in TNBC. Methods Immunohistochemical staining was performed to assess SPDEF expression across different breast cancer subtypes in samples collected at our center. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) and Western blot analyses were used to determine SPDEF expression levels in normal mammary epithelial cells and various breast cancer cell lines. SPDEF overexpression and knockdown models were established in MDA-MB-468 and MDA-MB-231 TNBC cells, respectively. Cell proliferation, migration, invasion, and apoptosis were evaluated using Cell Counting Kit-8 (CCK-8), colony formation, wound healing, Transwell invasion assays, and flow cytometry. Apoptosis-related protein expression was examined by Western blotting, and spatial transcriptomic data were integrated to analyze the spatial association between SPDEF and apoptosis-related genes. Results SPDEF expression was markedly reduced in TNBC tissues and cell lines, whereas significantly higher expression was observed in human epidermal growth factor receptor 2 (HER2) positive, luminal A, and luminal B breast cancer subtypes. Clinically, low SPDEF expression was significantly associated with advanced tumor-node-metastasis (TNM) stage and tumor recurrence in patients with TNBC. Survival analysis demonstrated that patients with high SPDEF expression exhibited signifi