Abstract In human medicine clinical trials are legally required for drug development and approval. In contrast, clinical trials in small animal cancer patients are less common and legally perceived as animal experiments. Comparative oncology has been recognized as a method to speed up the development of medications by introducing animal patients with naturally developing tumours. In such cases, using animal patients would generate more robust data, as their spontaneous disease resembles the “real life” situation and thus could be more likely to predict the situation in human disease. This would not only provide veterinary oncology access to the latest developments in medicine before they are available for clinical use in animals, but could also lead to generation of clinical data in animal patients that could be translated to humans. Nevertheless, there are several limitations to practical conduct of clinical trials in veterinary medicine. In this review, the possible application of similar standards of Good Clinical Practice as in human clinical drug development will be discussed in detail, with special consideration of legal and ethical aspects in Europe and the US.