Prevalence of CD20 ⁺ cutaneous epitheliotropic T-cell lymphoma in dogs: a retrospective analysis of 24 cases (2011–2018) in the USA

Background: Limited information is known about the baseline frequency of canine CD20 positive ( ⁺ ) cutaneous epitheliotropic T-cell lymphoma. A single canine case report has been published. Objectives: To characterize the baseline frequency of CD20 ⁺ staining in cases of canine cutaneous epitheliotropic T-cell lymphoma; to assess its values as a prognostic indicator. Animals: Skin biopsies from 24 client-owned animals diagnosed with cutaneous epitheliotropic lymphoma were assessed. Methods and materials: A retrospective review of medical records from 2011 to 2018. Clinical histories and previous histological and immunohistochemical slides were collected from 24 dogs and additional immunohistochemical staining was performed as needed to assess cases of cutaneous epitheliotropic T-cell lymphoma for CD3, CD20, CD79a and PAX5 staining characteristics. Staining characteristics were assessed for their statistical relationship to median survival time. Results: Overall median survival time was 189 days following the onset of clinical signs and 99 days following definitive diagnosis; 54% of cases had CD20 ⁺ staining. There was no statistically significant correlation between staining characteristics and median survival time from onset of signs (P = 0.54) or from diagnosis (P = 0.61). Conclusions and clinical significance: Canine cutaneous epitheliotropic lymphoma has a higher instance of CD20 positivity than documented previously. This indicates that CD20 staining may be unsuitable to differentiate T-cell and B-cell cutaneous epitheliotropic lymphoma. This also may have therapeutic implications with the advent of canine CD20 monoclonal antibody therapies.