Abstract
Mortality statistics for cancer in various countries and periods of time indicate that there has been little effect of industrialization on the inherent or spontaneous rate of occurrence of cancer. From U.S. cancer statistics and the BEIR values [Report of the Advisory Committee on the Biological Effects of Ionizing Radiation (1979)] for radiation dose response, the ionizing radiation exposure required to produce a number of cancers equal to this spontaneous incidence was estimated to lie between 450 and 2100 rads (1 rad = 0.01 J/kg). From these "cancer equivalent" doses the number of single-strand DNA breaks required to produce the spontaneous cancers is estimated to be 0.26-1.3 per cell DNA per day. It is suggested that the univalent reduction of oxygen in normal metabolism to O2- and subsequent production of more harmful radicals is the source of the DNA defects that, in cases where the defense mechanisms fail, lead to spontaneous cancer in the individual.