Method for reducing development of free radical induced malignancies

A method of reducing the risk of a patient developing a free radical induced malignancy, said method comprising administering an effective amount of a compound of formula I:

• ##STR4## wherein:
• R.sub.1 is lower alkyl or ##STR5## R.sub.2 and R.sub.4 are each individually SO.sub.3.sup.- M.sup.+, PO.sub.3.sup.2- M.sub.2.sup.2+, or PO.sub.2 S.sup.2- M.sub.2.sup.2+ ;
• R.sub.3 and R.sub.5 are each individually hydrogen, hydroxy or sulfhydryl;
• m and n are individually 0, 1, 2, 3 or 4, with the proviso that if m or n is 0, then R.sub.3 is hydrogen;
• and
• M is hydrogen or an alkali metal ion;
• or
• a pharmaceutically acceptable salt thereof.