a little CASE help, please

Hi there.  I've got a proc that presently uses this CASE stmt to drop the last two characters of an ordernumber --- _B and/or _S.  I need to use very similar logic to do the same thing, but with one additional requirement.  this is my stmt:  

select case when charindex('_',ordernumber)>1 then left(ordernumber,charindex('_',ordernumber) -1) else ordernumber end as ordernumber
from database

so this:  000008915_B
becomes this:  000008915

very good.  but, i need to also drop the zeros that preface the 8915.  see, there is an unknown number of zeros prefacing the order number, i need them gone such that this:  000008915_B
becomes this:  8915

sometimes it's one, it's three or four....like i said, it's an 'unknown' number of zeros. i just need to strip the prefacing zeros.

can anybody help me out w/this?