During 4NQO carcinogenesis basal lamina between epithelia and connective tissue is progressively destroyed (PAS histochemistry): Histological sections of control, healthy tongue ((a)-(b)), mild ((c)-(d)), moderate ((e)-(f)), and severe ((g)-(h)) dysplasia as well as OSCC ((i)-(j)) were stained with the PAS method for the detection of glycosylated components. PAS reactivity is progressively loss and completely absent in areas of OSCC, particularly in areas of connective tissue invasion. Bar scales: 50 μm ((a), (c), (e), (g), and (i)), 25 μm ((b), (d), (f), (h), and (j)).