When comparing the expression of the above mentioned marker proteins (except for p53) in matched pairs (n = 32 biopsies from 20 patients) of exophytic and concomitant stroma-invasive tumor areas (Online Resource 1), no significant difference in the expression of marker proteins, except for a reduction in KRT20 protein expression in the stroma-invasive tumor area (p < 0.01), was noted (Online Resource 6). Here, KRT20 is linked to neoplasm.