After either Nrf1α−/− HEA157 or Nrf1+/+ HepG2 hepatoma cells were inoculated subcutaneously into the right upper back region of nude mice at a single site, the incubation period of carcinogenesis before the in situ emergence of visible tumour xenogafts derived from Nrf1α−/− cells was shortened to two-thirds of that of Nrf1+/+ cells-derived tumour xenografts (Fig. 8a, left panel). This evidence concerns the gene NRF1 and neoplasm.