Figure 3

Histological examination of the resected rectal tumor. (a,b) Hematoxylin and eosin (HE) staining showed diffuse and infiltrative proliferation of small tumor cells in the submucosal region (a, original magnification ×200) and through the muscularis propria (b, original magnification x400). Minimal cohesion was observed among the tumor cells, and each tumor cell had an eccentric nucleus and eosinophilic cytoplasm. (c-f) Immunohistochemical findings. The tumor cells were positive for CK7 (c) but not for CK20 (d). They were positive for Estrogen receptor α (e) but negative for E-cadherin (f). In (a) and (c-f), the lower half of each figure was occupied by the tumor cell nests in the submucosal region, whereas in the upper half, the background normal colon crypts were observed (original magnification ×200).