The role of the time of application of the promoter in two-stage chemically induced carcinogenesis in the oral mucosa: experimental study in the rat.

The purpose of this study is to determine the role of the time of application of the promoter (in this case, mechanical irritation) in two-stage chemically induced oral carcinogenesis. One hundred fifty-five male rats were divided into seven groups. Group 1, 2 and 3 each received two intraperitoneal injections of the carcinogen N-nitroso-N-methylurea (NMU): 50 mg/Kg BW. Mechanical irritation was applied on the left buccal mucosa, 7 days before the first injection of NMU (group 1), 16 days (group 2), and 80 days (group 3) after the carcinogenic administration. Animals of groups 4, 5, 6 and 7 served as controls. Only group 1 and 2 animals developed tumors in the irritated buccal mucosa. From the results of this study we conclude that the delay of the application of the promoter does not lead to tumor formation. This could be explained by the repair of the carcinogenic lesion at the cellular level.