Don't know much about cherry trees, but this non-cheerful site seems to.
http://homeguides.sfgate.com/brown-leaves-dead-branches-cherry-tree-57742.html

My cherry trees have been denuded of leaves and developing cherries by the pigeons! Only the ones right at the end of the wavy branches have so far survived, but when ripe can be reached by athletic Blackbirds.

welcome to GoY.
Have you had a late frost?
could you post a picture of the tree and its leaves etc.

My friend had a dwarf flowering cherry and one of the main branches died suddenly and when we cut it down it was full of bacterial canker. I thought of this immediately I read your question. Info. about it on this website and others:
http://www.gardenfocused.co.uk/fruitarticles/pest-disease/canker-bacterial.php . Is there any oozing from the branches at all? That's a sign of canker.