Histopathology of the surgical specimen using Periodic Acid-Schiff (PAS) staining. (a) A mucinous substance showing positive PAS staining was present in the lumen (arrow) (PAS ×100). (b) Dropwise PAS staining was found for a basement membrane-like material within and around alveolar nests in the form of a film (arrow). Deposition of abundant basal lamina material showing PAS staining was also observed (PAS ×200).
