During 4NQO carcinogenesis the ECM connective tissue is progressively remodeled: Histological sections of control, healthy tongue (a), mild (b), moderate (c), and severe (d) dysplasia as well as OSCC (e) were stained for picro sirius red histochemistry. All the samples show presence of collagen I fibers. Interestingly, in severe dysplasia and OSCC collagen III fibers can be observed (arrows). Bar scale: 50 μm.