A study of the influence of age on response to a carcinogen

In an experiment in which 20 μg of 3,4 benzpyrene (BP) was applied twice weekly to the clipped dorsal skin of mice from the age of 10 wk (140 mice), 25 wk (170 mice), 40 wk (220 mice) or 55 wk (420 mice), the authors found a logarithmic increase in incidence rates of epithelial tumours with duration of exposure to BP, but, given duration exposure, no evidence was found of either reduced or increased susceptibility to the carcinogen with advancing age. The findings indicate that the logarithmic increase in incidence of most kinds of cancer with age is unlikely to be secondary to an age related falling off in the efficiency of repair mechanisms or of immunological surveillance. However, this does not mean that such mechanisms are irrelevant to carcinogenesis, only that they are not the determinants of the logarithmic increase in cancer incidence rates with duration of exposure which the authors have observed.