Feline lymphoma (145 cases): proliferation indices, cluster of differentiation 3 immunoreactivity, and their association with prognosis in 90 cats

Paraffin‐embedded, formalin‐fixed tissue samples from 145 cats with lymphoma were analyzed for cluster of differentiation 3 (CD3, a surface antigen) immunoreactivity, argyrophilic nucleolar organizer region (AgNOR) frequency, and proliferating cell nuclear antigen labeling index (PCNA‐LI). This information along with signalment, anatomic site, and feline leukemia virus (FeLV) antigen status was used to determine the potential of these indicators to predict response to therapy, remission, and survival times, and to characterize cats with lymphoma in the era of general availability of FeLV testing and vaccination. Alimentary lymphoma, primarily occurring in older, FeLV‐negative cats, was the most common site of involvement. Although the majority of tumors from FeLV‐positive cats were CD3‐immunoreactive, only one half of CD3‐immunoreactive tumors occurred in FeLV‐positive cats. Median remission duration and survival times were 126 days and 143 days, respectively, for all cats. Measures of tumor cell proliferation (AgNOR frequency and PCNA‐LI) and CD3‐immunoreactivity were not predictive of outcome. When all prognostic factors were accounted for by multivariate analysis, response to therapy, FeLV status, and clinical substage were predictive of outcome. FeLV‐negative cats that achieved a complete response following induction therapy were likely to have durable (ie, > 6‐month) responses, particularly when doxorubicin was included in the chemotherapy protocol. However, FeLV‐positive cats had significantly shorter remission and survival times with available chemotherapeutic protocols.