Characterization of lymphocytes in canine gastrointestinal lymphoma.

Primary canine gastrointestinal lymphoma has been believed to be of B-cell origin based on the morphology and behavior of the neoplastic cells and the evidence from the human medical field. However, the neoplasms have not to date been characterized as to the origin of the cell population. Forty-four cases diagnosed as canine gastrointestinal lymphoma were retrieved from the records of the Veterinary Teaching Hospitals at the University of Minnesota and the University of Wisconsin-Madison. Four of the cases have been previously identified as epitheliotropic T-cell gastrointestinal lymphoma. Twenty-three of the dogs were female, with 11 intact and 12 neutered, and 21 of the dogs were male, with 12 intact and nine neutered. Sixteen breeds as well as individuals of mixed breeding were represented. The Boxer and the sharpei were the most commonly represented breeds with six individuals each. The age range of the dogs was 1.5-14.66 years, with two dogs identified as adult and two of unknown age. Archived tissue blocks of gastrointestinal samples were sectioned in duplicate and prepared for immunohistochemical staining with CD3 (T-cell marker) and CD20 (B-cell marker). In 75% of the cases examined under light microscopy, 50-95% of the neoplastic cells stained positively with CD3 and exhibited marked epitheliotropic behavior. In three of the cases, from 10% up to 50% of the neoplastic cells stained positively with CD20, with widely scattered CD3(+) cells. In the remainder of the cases, few to none of the neoplastic cells stained with either of the markers. This retrospective study shows that canine primary gastrointestinal lymphoma is more commonly of T-cell origin, rather than B-cell origin.