Break spaghetti into small pieces (2 to 8 cm) and cook according to package directions. Meanwhile, combine soup, mushrooms, cream, and tuna. Drain spaghetti and combine with mushroom-tuna mixture. Put into greased 2 to 2.5 quart casserole. Mix bread crumbs, cheese, and melted butter and sprinkle on top of mixture in casserole. Bake in hot oven (400F) 45 minutes to 1 hour or until browned and bubbly.