Fig. 2

Representative images of the last operation. a Abdomen CT showed more obvious rectal wall thickening and an inhomogeneous enhanced mass on the left side of rectum. b Transverse section of the mass demonstrated a tan-white to gray cut surface, and the surrounding adipose tissue was involved. c A solid and perivascular papillary growth pattern with extensive necrosis at low magnification. d Prominent squamous appearance with keratin pearl formation at higher magnification, and tumor giant cells were remarkable. e Low power field which contains both SCC (lower right) and NEC (upper left). f Higher magnification of NEC (left) and SCC (right). NEC showed a scant basophilic cytoplasm, “salt and pepper” chromatin, and inconspicuous nucleoli. SCC displayed a faintly stained cytoplasm and prominent nucleoli. Synaptophysin (g) was exclusively present in NEC, and p40 (h) was exclusively present in SCC