Abstract Recent years have seen an emergence of the field of comparative cancer genomics. However, the advancements in this field are held back by the hesitation to use knowledge obtained from human studies to study cancer in other animals, and vice versa. Since cancer is an ancient disease that arose with multicellularity, oncogenes and tumour‐suppressor genes are amongst the oldest gene classes, shared by most animal species. Acknowledging that other animals are, in terms of cancer genetics, ecology, and evolution, rather similar to humans, creates huge potential for advancing the fields of human and animal oncology, but also biodiversity conservation. Also see the video abstract here: https://youtu.be/UFqyMx5HETY