S100A4 and oral submucous fibrosis: Notably, S100A4 was detected in human gingival fibroblasts treated with arecoline and arecoline N-oxides; higher expression levels of S100A4 [44] and ZEB1 [45] were found in oral submucous fibrosis tissues and buccal mucosal fibroblasts, respectively, which indicated the development of oral submucous fibrosis from normal mucosal fibroblasts and the progression to cancer and metastasis.