Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally until cooked through but firm to the bite, 8 minutes. Drain.
Preheat oven to 350 degrees F (175 degrees C). Butter a 2 1/2-quart casserole dish.
Mix macaroni, tomato sauce, tuna, cottage cheese, onion, cream cheese, sour cream, and salt together in the prepared casserole dish. Stir bread crumbs and butter together in a bowl; spread over tuna mixture.
Bake in the preheated oven until casserole is cooked through and bubbling, 35 to 40 minutes.
