Looks like apple canker. No remedy I believe. Could go on for some time but I would say that it will kill the tree eventually.

Agree with Jimmy, just one glance at the image - canker!

If it doesn't completely girdle the tree it won't snap in a high wind so it should be around for a while. As long as it gives you a good yield keep the tree going.

Very unfortunate :(. Thanks, I appreciate the quick responses.