Immunohistochemical expression of BRD4 and MUC1 in Oral Lichen Planus: association with clinical subtypes and role as potential biomarkers of epithelial alteration

Oral lichen planus (OLP) is a chronic immune-mediated disorder recognized by the World Health Organization (WHO) as an oral potentially malignant disorder (OPMD). Differentiating inflammation-associated epithelial alterations from early dysplastic changes remains a diagnostic challenge, highlighting the need for objective molecular biomarkers. Bromodomain-containing protein 4 (BRD4) and mucin-1 (MUC1) are involved in transcriptional regulation and epithelial differentiation, respectively; however, their combined expression in OLP has not been previously investigated. A retrospective cross-sectional study was conducted on 25 formalin-fixed paraffin-embedded (FFPE) OLP cases and 5 normal oral mucosa controls. Immunohistochemical staining for BRD4 and MUC1 was performed. Nuclear expression of BRD4 and membranous/cytoplasmic expression of MUC1 were semi-quantitatively evaluated. BRD4 expression was assessed using the H-score, while MUC1 was evaluated based on percentage positivity. Associations with clinical subtypes and between markers were analyzed using non-parametric tests and effect size measures. BRD4 expression was detected in 88% of OLP cases, predominantly localized to basal–parabasal nuclei, with a median H-score of 120.9. MUC1 was positive in 84% of cases, with a median positivity of 71% and frequent full-thickness epithelial distribution (47.6%). Erosive OLP showed higher expression levels for both markers compared to non-erosive OLP, although these differences did not reach statistical significance (p > 0.05). A weak positive correlation between BRD4 and MUC1 was observed (Spearman’s ρ = 0.26), with a moderate effect size in categorical association (Cramér’s V = 0.30). This is the first study demonstrating BRD4 expression in OLP, with both BRD4 and MUC1 showing higher levels in erosive lesions. Expression patterns are more compatible with epithelial changes due to chronic inflammation than with a dysplastic transformation per se, although both processes share molecular characteristics that do not allow them to be clearly distinguished in this study. These findings are preliminary and require validation in larger prospective studies.