Perianal neuroendocrine tumor with suspected lymph node metastasis causing colonic compression and subsequent megacolon.

An 8-year-old spayed female domestic shorthair cat was presented with a 4- to 5-month history of a progressively growing mass above her anus and an inability to defecate for 3 to 4 wk. External perianal and internal regional masses were subsequently identified and diagnosed as tumors of neuroendocrine origin through surgical excision and histopathologic evaluation. The cat was treated with 2 courses of chemotherapy and radiation therapy.