If you are attempting what I think you want then you can't do that in Tabulate as a single step. The percent calculations have to use either the n or sum of a table, row or column and cannot do sum or row1 and row2.
So you may have to presummarize everything. Without specific data and actual expectation I can't get more specific for suggestions on how.
You could use ODS OUTPUT to write the tabulate table to a dataset. Then create the cum_pct var from the PCT var, followed by a proc print. Here's a schematic:
ods output tabulate.report.table=MYTABLE;
proc tabulate data=mydata ;
table .... ;
ods output close;
/* Assume the pct var name is var2_pctsum_0_var2 */
proc print data=want;