Free radicals in cancer.

It has been hypothesized that free radicals play a significant role in cancer. A historical review indicates a series of rises and falls in the acceptance of this hypothesis and it remains controversial. The strongest evidence for a critical role of free radicals in cancer is based on electron spin resonance (e.s.r.) data from lyophilized (freeze-dried) tumours. Recent results indicate that such data are artifactual in the sense that the observed signals are not directly related to free radicals existing before lyophilization. These data also indicate, however, that some of the observed changes are reproducible and may be indirectly linked to biophysical or biochemical changes that occur in tumour cells. A possible key to such a link is via antioxidants, especially ascorbic acid. It is now feasible to do experiments to definitively determine: (1) the generality of the effect of lyophilization on e.s.r. spectra of tumours; (2) the molecular nature of the free radicals observed in lyophilized tumours and normal tissues; (3) the effect of redox reactions and substances on the observed e.s.r. spectra; and (4) the occurrence of free radical changes during carcinogenesis.