<;P>;PROBLEM TO BE SOLVED: To provide an animal model for spontaneous de novo cancer. <;P>;SOLUTION: The rodent gene modified animal to which an activated RET gene is transferred in a hetero type and which is deficient in an endothelin receptor B gene in a hetero type and naturally has an onset of de novo melanoma is provided. <;P>;COPYRIGHT: (C)2011,JPO&INPIT