Novel perianal proliferative mass in a 10.5‐year‐old male castrated dog

Abstract A 10.5‐year‐old, 31.1‐kg male castrated mixed‐breed dog was referred for a 1.5 cm, bleeding, perianal mass. Cytology was supportive of sarcoma, while granulation tissue with ulceration and superficial bacterial colonisation was reported on the histologic examination of an excisional biopsy performed by the referring veterinarian. Three months later, the dog presented for tenesmus and a large, ulcerated, bleeding recurrent perianal mass was noted. A second excisional biopsy was performed to alleviate clinical signs. The dog recovered from both procedures uneventfully and there were no wound‐related complications. Histologic assessment identified both a subcutaneous mesenchymal tumour (soft tissue sarcoma, grade 3) and a perianal gland atypical round cell population. Combined histopathology, immunohistochemical labelling and PCR for B‐cell antigen receptor rearrangement confirmed that the round cell population was consistent with a large B‐cell lymphoma.