We describe a new electrohyperthermia (oncothermia) method and a tumor treatment system, which was developed to cure companion animals having spontaneously occurring tumors. This dedicated veterinary oncothermia device plays a dual role; this can be a new hope to successfully treat companion animals having tumors. And during these treatments, we can get a large amount of valuable information about the real nature and parameter of the applied electromagnetic field and the behaviour of the tumor under this special modulated radiofrequency field. Then, this experience and knowledge can be transferred directly to the human clinical application to develop more precise treatment systems for human clinical oncology.