At the end of the DLC you fight and kill the breeder (similar to planting the bomb and escaping in the first extinction). The breeder isn't hard as long as you have a good team. I made it to the end many times and failed only because someone always ends up getting disconnected. Make sure you have at least 1 medic and 1 engineer and you should have no troubles. If you require help feel free to add me and ill be happy to help (xbox one not xbox 360)
*note the first time you encounter the breeder (after destroying the hives), you don't kill him, so to clear this up you must reach the end, not beat him off on the first encounter.