The effect of dose on cancer latency period.

A number of animal carcinogenesis experiments have demonstrated that the time from initial exposure to first detection of tumors increases with decreasing dose. This observation has led to some speculation that at very low doses tumors would take so long to develop that life would end before tumors appeared. We show that the apparent increase in tumor development time can be easily seen as nothing more than a manifestation of the mathematical fact that decreasing the incidence necessarily increases the first time-to-tumor. No physical increase in tumor growth time need be postulated to explain the observations. Existing methods of low-dose risk extrapolation implicitly account for the increase in time-to-tumor statistics insofar as they account for the decrease in tumor incidence.