There are certain federally-mandated conditions (revolving around military service) which entitle renters to early release from a lease.
But if you're just an ordinary "Joe and Jane" signing a 12-month lease, then no. Of course you can't break the lease. You committed to 12 months.
What you might consider is signing a 6 month lease. Or a 6-month lease with a right to renew for another 6 months. Or a 12-month lease with some sort of penalty provision--but something less harsh than if you broke the 12 month lease. But never, ever sign a 12-month lease if you think there's a possibility that you'll only be there for 6 months. It isn't fair to the owner, and you can get into a lot of hot water.