Figure 2.

Histological findings of the tumor. a. The tumor was encapsulated but extracapsular invasion was partially observed. Papillary-cystic proliferation was observed within the tumor. Hematoxylin eosin (HE) stain, loupe. b. The tumor cells exhibit markedly papillary proliferation with a cribriform pattern. Comedonecrosis is not observed. HE stain, original magnification ×100. c. Thickened basement membranes were observed around the tumor cell nest. PAS reaction, ×400. d. Cuboidal tumor cells lining cystic spaces have eosinophilic cytoplasm and exhibit an apocrine-like appearance with decapitation. HE stain, ×400. e. Apocrine-like tumor cells have cytoplasmic PAS-positive/diastase-resistant granules. PAS reaction with diastase digestion, ×400. f. The tumor cells phagocytose hemosiderin in the vicinity of hemorrhage. HE stain, ×400. g. Some tumor cells have foamy cytoplasm similar to sebaceous cells. HE stain, ×400. h. Cords and tubules of the tumor infiltrate the stroma with sclerosis. HE stain, ×200.