Activation of Wnt/β-catenin signaling in histologically non-dysplastic non-homogeneous oral leukoplakia

PURPOSE: Oral potentially malignant disorders (OPMD) are lesions that precede oral cancer in approximately 15-40% of cases. Leukoplakia is the most frequent type of OPMD, and is clinically classified as homogeneous oral leukoplakia (HOL) or non-homogeneous oral leukoplakia (NHOL) according to lesion color, surface characteristics, and clinical uniformity. Compared to HOL, NHOL is less frequent and is associated with higher malignant transformation rates. This difference is even more evident in lesions histopathologically diagnosed as non-dysplastic, including hyperplasia and hyperkeratosis. To the date, there is no signaling pathway that may explain this. We and others have shown that the Wnt/β-catenin pathway, characterized by stabilization and nuclear translocation of β-catenin for expression proliferation and survival genes, is key for dysplastic HOL carcinogenesis. The role of the Wnt/β-catenin pathway in dysplastic and non-dysplastic NHOL remains unknown. METHODS: Fifty-seven retrospective biopsies from patients with NHOL and HOL were used. Histological diagnosis was performed with Hematoxylin & Eosin (H&E) staining, while Wnt/β-catenin activity of signaling pathway was evaluated by immunohistochemical expression of the ligand Wnt3a and nuclear localization of β-catenin, as well as downstream proliferation markers Cyclin D1 and Ki-67. RESULTS: NHOL lesions histologically diagnosed as hyperplasia/hyperkeratosis (non-dysplastic), displayed significantly higher expression of Wnt3a and nuclear β-catenin, as well as Cyclin D1 and Ki-67, compared to non-dysplastic HOL and healthy oral mucosa. No significant differences were observed when comparing Wnt3a, nuclear β-catenin, Cyclin D1 and Ki-67 expression between non-dysplastic HOL and healthy oral mucosa. Both dysplastic NHOL and HOL samples, compared to healthy oral mucosa, presented significant upregulation of Wnt3a, nuclear β-catenin, Cyclin D1 and Ki-67. No significant differences in Wnt3a, nuclear β-catenin, Cyclin D1 and Ki-67 expression were observed between dysplastic NHOL and HOL. CONCLUSIONS: We conclude that, in clear contrast to non-dysplastic HOL, Wnt/β-catenin activity is increased in non-dysplastic NHOL, which correlates with the expression of downstream proliferation markers. Additionally, both dysplastic NHOL and HOL present high Wnt/β-catenin activity, regardless of the dysplasia grade.