A = the tumour infiltrates the mucosa in the form of irregular islands and sheets (yellow arrow). Lobules of minor salivary glands (red arrow) (hematoxylin and eosin stain, original magnification x40).
B = low magnification showing a poorly differentiated adenocarcinoma, characterized by solid and trabecular growth with isolated glandular structures (hematoxylin and eosin stain, original magnification x100).
C = the tumour infiltrates beneath a surface squamous epithelium; the mucosa at the right is partly ulcerated (hematoxylin and eosin stain, original magnification x100).
D = the tumour cells possess vesicular nuclei with prominent nucleoli. The mitotic rate is high (hematoxylin and eosin stain, original magnification x200).