styryl sulfone compounds of the invention selectively inhibit proliferation of tumor cells , and induce apoptosis of such tumor cells , while sparing normal cells . the compounds , which are useful in the treatment of cancer , have the formula ii : wherein n is zero or one ; r 1 is selected from the group consisting of hydrogen , chlorine , fluorine and bromine ; r 2 is selected from the group consisting of hydrogen , chlorine , fluorine , bromine , methyl and methoxy ; and r 3 is selected from the group consisting of hydrogen , chlorine and fluorine ; provided , r 2 may not be methyl or methoxy when r 1 and r 3 are both hydrogen and n is zero or one ; and r 1 , r 2 and r 3 may not all be hydrogen when n is one , or the formula iii : wherein r 1 is selected from the group consisting of hydrogen , chlorine , fluorine and bromine or the formula iv : wherein r 1 is selected from the group consisting of fluorine and bromine , and r 2 is selected from the group consisting of 2 - chlorophenyl , 4 - chlorophenyl , 4 - fluorophenyl and 2 - nitrophenyl .