Mouse tumors tend to have different histology compared with human tumors of the same tissue type and mice with engineered mutations often develop different cancer spectrums, e.g., mice with constitutive heterozygous Rb mutations (Rb homozygous mutations are embryonic lethal in mice) only mainly develop pituitary adenosarcomas while children with inherited constitutive Rb mutations develop retinoblastomas [34]. This evidence concerns the gene RB1 and retinoblastoma.