stepAIC

Hi,

I tried to use stepAIC for a cox proportional model
(30 independent variables) built by coxph. I found
that no matter whether I used direction="forward" or
direction="backward" as an option in stepAIC, I
alweays got exactly the same output, i.e. it seems
only backward selection was performed (eliminate 1
variable at a time). why did it happen like this? or
for cox model, stepAIC can only perform backward
selection?

thanks

zander