Signals for a promoting action of radiation in cancer incidence data.

The two-stage clonal expansion model allows us in principle to separate the initiating and promoting action of radiation. Features of the relative risk functions which indicate the action of promotion most clearly are identified for acute and for protracted exposures. They are compared with data: for acute exposure, some results of a preliminary analysis of the atomic-bomb survivor data are given; for protracted exposure, patterns in the fatal lung tumours of radon-exposed rats are discussed.