I'm not an attorney, but typically you are contractually obligated once you a sign a PA lease, and can't back out.
If that upsets you, bear this in mind: Would you want landlords to be able to change their minds after signing a lease with you, and deciding at the last minute that they'd rather lease to their brother in law?
You may be able to negotiate something with the landlord, wherein they let you off the lease for a small fee or something.
Best of luck,
Brian

Here is a link that might be useful: PA lease