Inhomogeneity of stiffness and density of the extracellular matrix within the leukoplakia of human oral mucosa as potential physicochemical factors leading to carcinogenesis

Oral leukoplakia is a clinical term relating to various morphological lesions, including squamous cell hyperplasia, dysplasia and carcinoma. Leukoplakia morphologically manifested as hyperplasia with epithelial dysplasia is clinically treated as precancerous condition. Nevertheless, there is a lack of good markers indicating the transformation of premalignancies towards cancer. A better understanding of the mechanical environment within the tissues where tumors grow might be beneficial for the development of prevention, diagnostic, and treatment methods in cancer management. Atomic force microscopy (AFM) and immunohistology techniques were used to assess changes in the stiffness and morphology of oral mucosa and leukoplakia samples at different stages of their progression towards cancer. The Young's moduli of the tested leukoplakia samples were significantly higher than those of the surrounding mucus. Robust inhomogeneity of stiffness within leukoplakia samples, reflecting an increase in regeneration and collagen accumulation (increasing density) in the extracellular matrix (ECM), was observed. Within the histologically confirmed cancer samples, Young's moduli were significantly lower than those within the precancerous ones. Inhomogeneous stiffness within leukoplakia might act as “a mechanoagonist” that promotes oncogenesis. In contrast, cancer growth might require the reorganization of tissue structure to create a microenvironment with lower and homogenous stiffness. The immunohistology data collected here indicates that changes in tissue stiffness are achieved by increasing cell/ECM density. The recognition of new markers of premalignancy will aid in the development of new therapies and will expand the diagnostic methods.