Naturally occurring and N-nitrosomethylurea-induced lung tumors were studied in male F344/NCr rats by sequential histological, electron microscopic, and immunohistochemical methods. Rats were given one injection at 6 weeks of age of N-nitrosomethylurea at a dosage level of 41.2 mg/kg body weight i.v. Groups of rats were sacrificed at 20, 33, and 52 weeks, while some were sacrificed while moribu...
