Fig. 4

Histological findings of the initial primary lesion. a The tumor consists of a mixture of atypical squamous cells and mucus-producing cells with solid cell sheets and no gland formation (hematoxylin and eosin, ×40 objective lens magnification). b Immunohistochemically, the tumor cells stain positive for cluster of differentiation (CD) 5 (×100 objective lens magnification)