In a bowl combine; Worcestershire sauce, soy sauce, sugar and the juice from the pineapple cans (set the chunks or slices aside) and stir well. Using a fork, poke about 5 to 8 sets of holes in each chicken breast and put chicken in marinade, making sure it is covered in the mixture, add more pineapple juice if necessary. Cover and refrigerate for 24-36 hours, then line a cookie sheet with buttered aluminum foil and place the marinated chicken on the foiled tray and cover the chicken with the pineapple slices or chunks. Bake uncovered at 350 for about 45 minutes or until done