Carcinogenic effects of combined treatment of inbred mice with 3-methylcholanthrene and 1,2-dimethylhydrazine.

Inbred mice of strains C57BL/6J (B6) (Ahb/-Ahb) and DBA/2J (D2) (Ahd/Ahd) were administered 3-methylcholanthrene (MCA) alone, 1,2-dimethylhydrazine (DMH) alone, and MCA and DMH together. Colorectal tumors were observed in 32% of the DMH-treated B6 mice, but no such tumors occurred in similarly treated D2 mice. Of the MCA-treated D2 mice, 46% were susceptible to leukemia, whereas in similarly treated B6 mice, 19% developed only lung tumors. The combined application of MCA and DMH resulted in an increased incidence of colorectal (52%) and lung (44%) tumors in B6 mice and, to some extent, of leukemia (63%) in D2 mice. The role of genetic background on the carcinogenic effects of combined application of MCA and DMH in inbred mice is discussed.