Activation of Wnt/β-catenin signaling in histologically non-dysplastic Proliferative Verrucous 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 according to the roughness of the lesion surface is clinically classified as homogeneous oral leukoplakia (HOL) or proliferative verrucous leukoplakia (PVL). Compared to HOL, PVL 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 PVL remains unknown. Methods: 53 retrospective biopsies from patients with PVL 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: PVL 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 PVL 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 PVL and HOL. Conclusions: We conclude that, in clear contrast to non-dysplastic HOL, Wnt/β-catenin activity is increased in non-dysplastic PVL, which correlates with the expression of downstream malignant proliferation markers. Additionally, both dysplastic PVL and HOL present high Wnt/β-catenin activity, regardless of the dysplasia grade.