Using a bunt microwave pan, spray with non stick vegetable spray. Melt butter and pour into bunt pan. Spread brown sugar in bottom of pan on butter. Place pineapple slices around on top of brown sugar. Save the juice. Slice the cherries and place in and around the pineapple slices. Mix pineapple juice and one egg in the half of boxed cake mix. Pour over pineapple slices, cherries and brown sugar. Bake in microwave on high for 9 minutes on turn table. If you don't have a turn table, turn 1/4 turn every 3 minutes.