Histology of the tumor (Hematoxylin and eosin; ×400). Near the fibrotic focus, the tumor cells pack and fill the alveolar spaces (A). Alveolar septae are well preserved. Even in the space where the tumor seems to be absent macroscopically, tumor cells are seen to be diffusely floating in the alveolar spaces (B). Dissociated tumor cells invading the peripheral sinus of the lymph nodes singly and diffusely (C).