Immunohistochemical Evaluation of ALDH1 and Maspin in Oral Potentially Malignant Disorders and Oral Carcinoma

<b>Background/Objectives</b>: Oral potentially malignant disorders (OPMDs), including oral leukoplakia (OLK), oral lichen planus (OLP), and actinic cheilitis (AC), have varying risks of progression to oral squamous cell carcinoma (OSCC). Biomarkers such as aldehyde dehydrogenase 1 (ALDH1) and mammary serine protease inhibitor (Maspin) have shown potential for diagnostic and prognostic use in oral cancer. The present study aimed to evaluate the immunoexpression of aldehyde dehydrogenase 1, a cancer stem cell marker associated with aggressiveness, and the mammary serine protease inhibitor, a potential tumor suppressor, in OPMD and OSCC tissues. <b>Methods</b>: A retrospective analysis was performed on 145 biopsy specimens collected from January 2015 to January 2023, including normal epithelium, OPMDs (OLK, OLP, AC), and OSCC. ALDH1 and Maspin expression levels were evaluated using immunohistochemistry, considering both the percentage of positive cells and staining intensity. Statistical analyses were carried out using the Statistical Package for the Social Sciences (SPSS, version 29.0; IBM Corp., Chicago, IL, USA). <b>Results</b>: Normal oral epithelium showed no expression of ALDH1, whereas 40.6% of OPMDs and 44.4% of OSCC samples exhibited high cytoplasmic ALDH1 expression. Nuclear ALDH1 expression was elevated in 29.7% of OPMDs and 38.9% of OSCCs (<i>p</i> < 0.001). Nuclear Maspin expression was high in 95.2% of normal tissues, in 67.2% of OPMDs and in 55.6% of OSCCs (<i>p</i> < 0.001). Maspin showed strong nuclear and cytoplasmic expression in normal tissue, but its expression decreased in OPMDs and OSCCs, with statistically significant reductions in both compartments (<i>p</i> < 0.001). <b>Conclusions</b>: The results indicate that ALDH1 upregulation and Maspin downregulation are hallmark events in oral carcinogenesis. Their combined evaluation provides a powerful tool for assessing dysplastic severity and malignant transformation risk in OPMDs. Future studies on larger cohorts are needed to confirm the prognostic utility of this dual-marker model.