Histological Classification and Immunohistochemical Study of Feline Colorectal Epithelial Tumors.

Abstract

Among 113 feline gastrointestinal epithelial tumors diagnosed between 2006 and 2019, 78 (69%) were detected in the colorectum. Fifty colorectal tumors were selected for further pathological evaluations, of which 9 (18%) were histopathologically diagnosed as adenomas and 41 (82%) as carcinoma. The carcinomas included 33 tubular adenocarcinomas (TAC), 5 tubulovillous adenocarcinomas (TVAC), 2 mucinous adenocarcinomas, and 1 undifferentiated carcinoma. Histopathologically, TAC frequently showed vascular invasion (17/33 cases, 52%). In TAC cases, serosal infiltration (13/15 cases, 87%) and lymph node metastasis (8/9 cases, 89%) were common in bowel resection and lymphadenectomy samples, respectively. Immunohistochemically, the tumor cells of most cases were positive for cytokeratin (CK) 20 (50/50 cases, 100%) and CDX2 (48/50 cases, 96%). Focal immunopositivity for CD10 (11/50 cases, 22%) and CK7 (15/50 cases, 30%) was observed irrespective of the histological subtype. Only a few cases showed diffuse nuclear accumulation of &#x3b2;-catenin (2/50 cases, 4%) and p53 (5/50 cases, 10%). A lack of tubule formation, female sex, and low CDX2 labeling were statistically associated with carcinoma compared to adenoma (&#x3c1; = 0.615,< .001; &#x3c1; = 0.279,= .050; and &#x3c1; = -0.265,= .063, respectively). Other features, including mucin profiles, Ki67 labeling index, and accumulation of &#x3b2;-catenin and p53, were not associated with malignancy. A sequence analysis revealedmutations in 3/7 TAC cases. These results suggest thatmutations-rather than excessive Wnt/&#x3b2;-catenin signaling and the inactivation ofcontribute to the tumorigenesis of feline colorectal carcinoma.