Pathology of rectal tubulopapillary adenocarcinoma in a Labrador

Abstract

Rectal adenocarcinoma is the most common type of large intestinal tumour in dogs. A seven year old intact Labrador was presented for the evaluation of a mass in the rectum. Rectal examination revealed a soft mass on the right lateral wall of the distal part of the rectum. Histologically, the tumour mass composed of tubules and papillary projections in the lumen and lined by pleomorphic columnar cells. Neoplastic cells have distinct cells borders with moderate to abundant eosinophilic cytoplasm containing large vacuoles which was positive in PAS staining. Immunohistochemically, the columnar epithelial cells were positive for pan-cytokeratin while vimentin is positive in the stromal cells in between the tubules indicative of mesenchymal tissue. Based on the gross, histopathological and immunohistochemical features, the case was diagnosed as rectal tubulopapillary adenocarcinoma in a dog.