Expression of FAP in Oral Leukoplakia and Oral Squamous Cell Carcinoma

Objective: This study aimed to investigate the potential of fibroblast activation protein (FAP) as a biomarker in the progression of oral leukoplakia (OLK) carcinogenesis. This was achieved by evaluating FAP expression at different levels of the organisation, namely oral normal mucosa (NM), OLK, and oral squamous cell carcinoma (OSCC). Materials and methods: Altogether, 88 paraffin-embedded tissue samples were examined, including 55 cases of OLK, 13 cases of OSCC, and 20 cases of NM (control group). An exhaustive investigation was performed to examine FAP expression in NM, OLK, and OSCC tissues via immunohistochemistry (IHC). The relationship between FAP expression and clinical pathologic characteristics was analysed. Reverse transcription-polymerase chain reaction (RT-PCR) and western blot (WB) also proved the expression of FAP in NM, OLK, and OSCC cells. Aberrant FAP expression in OLK and OSCC was explored using in vitro experiments. Results: Immunohistochemical results showed that high FAP expression was significantly correlated with histopathologic grade (P = .038) but not correlated with age, sex, or region (P = .953, .622, and .108, respectively). The expression level of FAP in NM tissues (0.15 +/- 0.01) was minimal, whereas it was observed in OLK (0.28 +/- 0.04) and OSCC (0.39 +/- 0.02) tissues with a noticeable increase in expression levels (P < .001). The expression level of FAP in OLK with severe abnormal hyperplasia (S-OLK) tissues (0.33 +/- 0.04) was significantly higher than in OLK with mild abnormal hyperplasia (MI-OLK, 0.26 +/- 0.02) and OLK with moderate abnormal hyperplasia (MO-OLK, 0.28 +/- 0.03) tissues (P < .001 and P = .039, respectively). The results of RT-PCR illustrated that the relative expression of FAP mRNA in OLK cells (2.63 +/- 0.62) was higher than in NM cells (0.87 +/- 0.14), but lower than in OSCC cells (5.63 +/- 1.06; P = .027 and .012, respectively). FAP expression was minimal in NM cells (0.78 +/- 0.06), modest in OLK cells (1.04 +/- 0.06), and significantly elevated in OSCC cells (1.61 +/- 0.09) based on the results of WB (P < .001). Conclusions: Significant variations in FAP expression were observed in NM, OLK, and OSCC tissues and cells. These findings revealed that FAP may be a reliable biomarker for the early diagnosis and evaluation of OLK carcinogenesis. (c) 2024 The Authors. Published by Elsevier Inc. on behalf of FDI World Dental Federation. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)