Discovery and validation of a prognostic SPP1/PLAU signature in HPV-negative oropharyngeal squamous cell carcinoma

BACKGROUND: This study aimed to identify and validate robust prognostic biomarkers for oropharyngeal squamous cell carcinoma (OPSCC), with a specific focus on the high-risk HPV-negative subtype. METHODS: Integrated bioinformatics analysis was performed on transcriptomic data from four GEO datasets (n = 418 samples). Differentially expressed genes (DEGs) were identified, and a protein-protein interaction (PPI) network was constructed for the most dysregulated genes. Key modules were analyzed via survival analysis and multivariate Cox regression. The top candidate genes were validated at the protein level using immunohistochemistry (IHC) in an independent cohort of 304 OPSCC patients. RESULTS: A 33-gene module related to extracellular matrix organization showed significant prognostic association. It stratified patients into high- and low-risk groups with markedly different overall survival (HR = 2.71, p < 0.001). From this module, SPP1 and PLAU were identified as independent prognostic factors through multi-step screening. Both genes were significantly overexpressed in tumors (approximately 20-fold and 10-fold, respectively, p < 0.001), with high expression strongly correlated with advanced tumor stage (p < 0.01) and, notably, the HPV-negative subtype (p < 0.001). In survival analysis, high expression of either SPP1 or PLAU was associated with poorer overall survival (SPP1: p < 0.001; PLAU: p < 0.001) and progression-free survival (p < 0.001). IHC validation confirmed high protein expression in 69.7% (SPP1) and 54.8% (PLAU) of cancer tissues. A prognostic nomogram integrating the SPP1/PLAU signature with clinical variables was constructed with strong predictive accuracy (C-index = 0.75). CONCLUSION: The SPP1/PLAU dual-gene signature is a robust and independent prognostic biomarker for OPSCC, with particular clinical utility for stratifying high-risk HPV-negative patients.