A pharmaceutical composition for treatment of cancer comprises:(A) a therapeutically effective amount of at least one compound selected from the group consisting of compounds represented by the General Formula (I) ##STR1## wherein X.sub.1 and X.sub.2, which may be the same or different, each represents O, S, Se, --CH.dbd.CH--, ##STR2## Y.sub.1 represents O, S, Se, or ##STR3## R.sub.1 and R.sub.3, which may be the same or different, each represents an alkyl group;R.sub.2 represents an alkyl group, an aryl group or a heterocyclic group;Z.sub.1 and Z.sub.2, which may be the same or different, each represents an atomic group necessary to form a 5- or 6-membered ring;L.sub.1 represents a methine group or L.sub.1 and R.sub.3 may combine and form a 5- or 6-membered ring;R.sub.4 and R.sub.5, which may be the same or different, each represents a alkyl group;R.sub.6 and R.sub.7, which may be the same or different, each represents an alkyl group or an aryl group;Q represents a pharmaceutically acceptable anion;l represents 1 or 2;m and n, which may be the same or different, each represents 0 or 1; and(B) a pharmaceutically acceptable carrier or diluent.