Human and zebrafish genomes are 70% similar based on conservation of individual genes (Table 1), with several cancer-associated genes found in mammals but not in the zebrafish, including BRCA1, p16 (CDKN2A), BRCA1, LIF, OSM, IL6 (Howe et al., 2013) and PML (G.D. and J.N.B., unpublished observation). This evidence concerns the gene LIF and cancer.