Heterogeneity of cancer risk due to stochastic effects: emphasis on radiation-induced effects.

Persons with exactly the same genetic background, behavior and environment may differ in radiation cancer risk, due to the stochastic nature of cancer development. These differences are estimated quantitatively by means of the two stage clonal expansion model, in which the number of intermediate cells on their way to malignancy varies stochastically between individuals. For liver cancer after injection of Thorotrast, the estimated relative risk for persons without intermediate cells at age 40 is a factor of more than 10 larger than that for persons with a large number of intermediate cells. The population-based estimate of the relative risk represents an underestimation for most persons at most ages, because for persons showing a large number of intermediate cells liver cancer is not a rare disease.