As in mice, Xenopus tumours require inactivation of both rb1 and rbl1 genes, achieved by co-injection of independent pairs of guide RNAs and editing by CRISPR-Cas9; these mosaic double knock-out tadpoles develop a rapid and penetrant retinoblastoma in as little as 35 days, with histopathology and disease progression conserved with the human tumour (Naert et al., 2016). The gene discussed is RB1; the disease is neoplasm.