Induction of liver cell adenomata in the rat by a single treatment with N-methyl-N-nitrosourea given at various times after partial hepatectomy.

A single treatment of adult animals with the potent carcinogen NMU was known to induce tumours in a wide variety of organs, with the notable exception of liver. Administration of NMU after partial hepatectomy gave rise to the first liver cell adenomata ever observed in rats due to this carcinogen. The tumours were induced when NMU was given during the period of increased DNA synthesis but not when given early in the pre-replicative period. Although tumours were induced in other organs, the incidence of these did not correlate with the timing of NMU administration. It is suggested that replication of damaged DNA may be a relevant event in carcinogenesis.