Melt butter in pan over low heat. Stir in flour, salt, pepper, mustard, and Worcestershire sauce. Cook over low heat, stirring constantly, until mixture is smooth and bubbly. Stir in milk. Heat to boiling, stirring constantly. Boil and stir minute. Stir in cheese until melted.
Add macaroni, chicken, broccoli, and tomatoes.
Pour into 2 quart casserole dish. Top with breadcrumbs. Bake uncovered 20 to 25 minutes or until bubbly.