Preclinical imaging and treatment of cancer: the use of animal models beyond rodents.

The development of novel radiopharmaceutical agents for imaging and therapy of neoplastic diseases relies on accurate and reproducible animal models. Rodent models are often used to demonstrate the proof-of-principle tracer and therapeutic agent development, but their small size can make tissue sampling challenging. The dosimetry of decay emissions in the much smaller rodent tumors do not model dosimetry in human tumors well. In addition, rodent models of cancer represent a simplified version of a very complex process. Spontaneous tumors are heterogenous and the response to intervention can be unpredictable; tumor cells can adopt alternate signaling pathways and modify their interaction with the microenvironment. These inconsistencies, while present in humans, are difficult to fully reproduce in a genetically-engineered rodent model. Companion animals, primarily dogs and cats, offer translational models that more accurately reflect the intricate nature of spontaneous neoplasia in humans. Their larger size facilitates tissue and blood sampling when needed, and allows radiopharmaceutical tracers to be studied on human-scale imaging systems to better mimic the clinical application of the agent. This article will review the growing body of literature surrounding the use of radiopharmaceutical agents for both imaging and therapy in companion dogs and cats. Previous investigations have been performed both for the advancement of routine, high-level veterinary care, and in the context of translational research from which the results of imaging and treatment can be readily applied to people. Studies utilizing the spontaneously occurring cancer model in companion animals involving positron emission tomography, radiotracers, dosimetry, theranostics, targeted radiopharmaceuticals, brachytherapy, and boron neutron capture therapy are discussed.