In veterinary medical oncology, there is currently no standardized protocol for assessing response to therapy in solid tumours. The lack of such a formalized guideline makes it challenging to critically compare outcome measures across various treatment protocols. The Veterinary Cooperative Oncology Group (VCOG) membership consensus document presented here is based on the recommendations of a subcommittee of American College of Veterinary Internal Medicine (ACVIM) board-certified veterinary oncologists. This consensus paper has used the human response evaluation criteria in solid tumours (RECIST v1.1) as a framework to establish standard procedures for response assessment in canine solid tumours that is meant to be easy to use, repeatable and applicable across a variety of clinical trial structures in veterinary oncology. It is hoped that this new canine RECIST (cRECIST v1.0) will be adopted within the veterinary oncology community and thereby facilitate the comparison of current and future treatment protocols used for companion animals with cancer.

Spontaneous tumors in companion animals (dog and cat) offer a unique opportunity as models for human cancer biology and translational cancer therapeutics. The relatively high incidence of some cancers, similar biologic behavior, large body size, comparable responses to cytotoxic agents, and shorter overall lifespan are the factors that contribute to the advantages of the companion animal model. The tumor types that offer the best comparative interest include lymphoma/leukemia, osteosarcoma, STS, melanoma, and mammary tumors. With the increase in new therapeutic agents (traditional chemotherapy, gene therapy, biologic agents, etc.), the companion animal model can provide useful populations to test new agents where efficacy and toxicity can be examined.

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 FeLVpositive 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. FeLVnegative cats that achieved a complete response following induction therapy were likely to have durable (ie, >6-month) responses, particularly when doxoruhicin was included in the chemotherapy protocol. However, FeLV-positive cats had significantly shorter remission and survival times with available chemotherapeutic protocols.Key words: AgNOR; Cancer; Feline leukemia virus; PCNA ymphoma (malignant lymphoma, lymphosarcoma) is L the most common malignancy in domestic cats and accounts for approximately one third of all tumors in this species.' Many cats with lymphoma will achieve remission and return to a good quality of life with appropriate therapy; however, predicting which cats will respond to therapy and which will not is a difficult challenge. termined that markers of proliferation (AgNOR frequency and PCNA-LI) and the cluster of differentiation 3 (CD3, a surface antigen) T-cell phenotype are predictors of treatment response in dogs with lymph~rna.~ The purpose of this study was to determine, in a retrospective fashion, AgNOR frequency, CD3 immunophenotype, and PCNA-LI in a large group of cats with lymphoma and determine if their predictive ability holds true in this species. Such assays could provide rapid, clinically relevant information to better educate clients as to the expected response to therapy as well as a means of prospectively tailoring individual treatments in future trials. In addition, many veterinary oncologists have noted an anecdotal change in the relative frequency of anatomic sites for lymphoma in the last 10-15 years, corresponding to the general availability of feline leukemia virus (FeLV) testing and vaccination programs. This study, therefore, also presents signalment and retroviral and anatomic site data on a large population of cats w...

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