ENDOU is potentially a robust diagnostic and prognostic biomarker in oral squamous cell carcinoma

Background Oral squamous cell carcinoma (OSCC) is responsible for approximately 190,000 deaths each year worldwide, primarily due to late-stage diagnosis. The lack of clinically useful biomarkers has been identified as one of the crucial factors contributing to diagnostic delay in OSCC, limiting the impact of tumor biology on treatment decisions and leading to poor prognosis. We investigated the clinical utility of tissue staining for ENDOU protein, a recently identified tumor suppressor in oral mucosa, as a biomarker for early OSCC detection. Additionally, using publicly available datasets and versatile systems biology tools we dissected the molecular profiles of low ENDOU expressing tumors and precancerous lesions to elucidate the role of ENDOU in the disease progression. Results Our results demonstrated consistent downregulation of ENDOU mRNA in OSCC in 11 independent discovery cohorts. In the validation cohorts, semi-quantitative immunohistochemical assessment revealed complete loss of ENDOU protein in 93% of tumors (p<0.001), which was independent of clinicopathological parameters such as TNM stage, tumor grade, age, or gender. The confusion matrix demonstrated high diagnostic accuracy of ENDOU staining in OSCC detection (0.93, 95% CI = 0.85-0.97; AUC = 0.95, 95% CI = 0.88-1.00, p<0.0001), which was significantly higher (p<0.05) compared to PDPN staining (0.76, 95% CI = 0.63-0.86), used as a reference biomarker in this study. Multivariate analysis demonstrated that ENDOU loss could serve as an independent adverse prognostic marker for OSCC (HR = 2.21, 95% CI = 1.22-4.01, p<0.01). Molecular profiling of low ENDOU expressing tumors and oral potentially malignant disorders (OPMDs) revealed its association with biological processes such as keratinocyte differentiation and immune response. Furthermore, low ENDOU expressing tumors exhibited hyperactivation of c-myc, and inhibition of p53 signaling pathways while in the precancerous lesions, ENDOU loss was associated with hyperactivation of early oncogenic pathways including JAK-STAT, angiogenesis and EMT. Conclusions Our study highlights the potential of ENDOU as a diagnostic biomarker for early detection of OSCC and disease prognostication. Moreover, loss of ENDOU is associated with perturbation of vital biological processes and signaling pathways in the context of oral carcinogenesis. Further studies are warranted to validate these findings and explore their clinical implications.