Peroxyl free radicals: potential mediators of tumor initiation and promotion.

In recent years, there has been an explosion of interest in the involvement of free radicals in carcinogenesis (1 -4) . This seems a natural outgrowth of the long overdue realization that free radicals are formed in biological systems and that they contribute significantly to physiological and pathological processes. Much of the emphasis of research linking free radicals and cancer has focused on intermediates of oxygen reduction such as superoxide anion and hydroxyl radical (2). There is another family of oxygencentered free radicals that have received less attention but may be just as important biologically as reduced oxygen intermediates. This Commentary is intended to familiarize the reader with some of the properties of peroxyl radicals and to explain how these species participate in reactions that are relevant to tumor initiation and promotion. Experimental data are presented that are intended to be provocative rather than definitive because this area of investigation is just beginning to evolve.