Leaking Toilet

WHEN FLUSHING MY 2nd FLOOR TOILET, WATER FLOWS DOWN THE MAIN STACK TO THE CELLAR. I BELIEVE THERE IS A CRACK IN THE MAIN STACK,
DOES ANYONE HAVE ANY REPAIR IDEAS, W/OUT REPLACING THE COMPLETE STACK???
THANKS,
JACKO

First of all, you have KNOW when the leak is for sure. It likely that it is in a connection since drain pipes themselves don't usually break. You should not have to replace the entire stack, but pieces will have to replaced. It's impossible to be more specific with the information given, including where the leak is, what kind of pipe your drain is, what access the is to the drain, etc..