Tumor response assessment in veterinary medicine and RECIST criteria

In human and veterinary medicine, cancer remains a major health problem, and the overall incidence of cancer continues to rise. Researchers are continually developing and testing new therapy options in cancer clinical trials to treat cancer in humans and animals more effectively. Cancer in companion animals has clinical and biological similarities to human cancers. Comparative oncology describes the study of naturally occurring cancers in animals as models for human disease. At the University Clinic of Companion Animals of Utrecht University, an example of such a study started in which the efficacy of intratumoral injections of radioactive holmium (166Ho) loaded microspheres by dogs and cats is investigated. The therapeutic effect of this brachytherapy technique will be assessed by evaluating tumor response. Today, in human medicine there is a set of published rules that are used in clinical trials to define when cancer responds, does not respond, or progresses, during or after treatment. These guidelines are called the Response Evaluation Criteria in Solid Tumors (RECIST). RECIST guidelines comprise definitions and criteria for assessment of tumor response, and also make recommendations regarding standardized reporting of the results of trials that utilize objective tumor response as an endpoint. It is important to use a diagnostic modality that accurately reflects the dimensions of the tumor. In order to make RECIST an acceptable method for the evaluation of tumor response in veterinary oncology, more research needs to be done. In this paper, a start is made by evaluating tumor response in a veterinary oncological trial using the RECIST criteria, based on the sum of unidimensional measurements of the longest diameter of the tumor