Molecular Characterization of Oral Epithelial Dysplasia and Oral Squamous Cell Carcinoma Using EGFR, CDKN2A, and HRAS Alterations

Background/Objectives: Oral squamous cell carcinoma (OSCC) often presents at an advanced stage; therefore, the early detection of precursor lesions is crucial. However, the risk assessment of precursor lesions such as oral epithelial dysplasia (OED) remains challenging because of the subjectivity of histopathological grading. We aimed to identify molecular markers that enhance the diagnostic accuracy and prognostic stratification of OSCC and explore the differences in the molecular characterization of OED and OSCC using a few selected markers. Methods: A two-step diagnostic workflow was applied: (1) FISH evaluation of EGFR amplification and CDKN2A deletion to distinguish OED from OSCC and identify EGFR-dependent tumors, and (2) HRAS immunohistochemistry performed exclusively in EGFR-negative OSCCs to stratify EGFR-independent cases. Fluorescence in situ hybridization (FISH) was used to assess seven EGFR/cell cycle-related genes (CCND1, CDKN2A, EGFR, PIK3CA, PTEN, TP53, and 1p36 locus) in 117 formalin-fixed paraffin-embedded samples (66 OED and 51 OSCC) and 10 normal mucosa samples. HRAS expression was evaluated using immunohistochemistry (IHC) in 36 EGFR amplification-negative OSCCs samples. Results: EGFR amplification was frequent in OSCC, whereas CDKN2A deletion was common in OED. The EGFR-amplified/ CDKN2A-intact profile showed high specificity for OSCC and improved diagnostic performance (area under the curve = 0.77) when combined with the Ki-67 labeling index. It also predicted poor disease-free survival (hazard ratio [HR] = 5.08, p = 0.016) and overall survival (HR = 6.10, p = 0.047). Among EGFR-negative OSCCs, HRAS overexpression was associated with advanced-stage disease and a poor prognosis (HR = 6.15, p = 0.043). Conclusions: EGFR amplification was frequent in OSCC, and CDKN2A deletion was prevalent in OED, supporting their use as molecular markers for differential diagnoses. FISH for EGFR/CDKN2A and HRAS IHC can stratify OSCC by diagnosis and prognosis, enabling practical molecular subclassification, including EGFR-negative cases.