Coexpression of CD3 and CD20 in Canine Enteropathy-Associated T-cell Lymphoma

The majority of primary intestinal lymphomas in dogs are T-cell lymphomas, with enteropathy-associated T-cell lymphoma (EATL) large cell type (type 1) being the most common. While most T-cell lymphomas express the T-cell marker CD3, there is increasing evidence that some human and canine T-cell lymphomas coexpress the B-cell marker CD20. We describe 3 cases of CD3⁺, CD20⁺, Pax5^- EATL type 1 in dogs. All 3 cases had clonal rearrangement of T-cell receptor gamma. Initial clinical signs included weight loss, inappetence, diarrhea, and/or vomiting. The mean age was 9 years (range 3-12). Survival was highly variable ranging from 20 days to longer than 1.6 years. Considering the different chemotherapeutic response of T-cell versus B-cell lymphomas, accurate diagnosis of lymphomas coexpressing CD3 and CD20 as EATL type 1 based on histologic features and clonality results is important. Regardless, the clinical and/or prognostic significance of neoplastic T cells expressing CD20 is unclear.