focal proliferative changes in the acinar cells of the pancreas of rats have been induced by several systemically administered carcinogens including azaserine , n - nitrosobis(2-oxopropyl)amine , n - nitroso-(2-hydroxypropyl ) ( 2-oxopropyl)amine , and n delta-(n - methyl - n - nitrosocarbamoyl)-l - ornithine ( mnco ) . 
 foci , nodules , and adenomas induced by these carcinogens are usually made up of atypical - appearing acinar cells that maintain a high degree of differentiation , but a minority of these lesions exhibit anaplastic cellular changes that suggest the development of malignant potential . 
 such anaplasia may occupy the whole of smaller lesions or may occur as a secondary focal change within larger nodules or adenomas . 
 many foci and nodules per pancreas have been induced by single or multiple exposures to these known genotoxic carcinogens , but relatively few of them develop into carcinomas . 
 azaserine and mnco have induced acinar cell carcinomas in rats . 
 those induced by azaserine have exhibited a broad spectrum of histologic variants , including ductlike cystic , and undifferentiated patterns . 
 higher doses of mnco have induced a second pattern of change in the pancreatic lobules of rats , which includes cystic and tubular ductlike structures that have been called cystic and tubular ductal complexes . 
 mnco has also induced focal acinar cell lesions , cystic and tubular ductal complexes , and adenocarcinomas in the pancreas of syrain golden hamsters . in this 
 species , ductal complexes are much more numerous than are proliferative lesions of acinar cells , and the histologic appearance of the carcinomas is ductlike . 
 hyperplasia and atypical changes were also seen in the epithelium of the intralobular ducts of hamsters.(abstract truncated at 250 words)imagesfigure 1.figure 2.figure 3.figure 4 .