Carcinoma in situ within an area of Barrett esophagus in a dog with megaesophagus.

A 10-y-old Irish Setter was presented with a history of recurrent episodes of regurgitation and vomiting, with more recent development of tachypnea. Megaesophagus had been diagnosed in the dog 2 y prior to this presentation. A solitary polypoid mass present immediately rostral to the lower esophageal sphincter was biopsied during percutaneous endoscopic gastrostomy tube placement. Barrett esophagus was diagnosed based on the observation of a polypoid mass with intestinal metaplasia that arose from the surrounding esophagus. Histology of the polypoid mass demonstrated squamous-to-columnar metaplasia, hyperplasia, dysplasia, and carcinoma in situ.