'Til noon, the center of Milan will be criss-crossed by the runners of the Deejay 10 marathon.
All busses and trams criss-crossing the center of town have been deviated until at least noon, though the metro should not be affected (except by heavier than usual crowds).
The day should be lovely in the afternoon, though, so don't renounce the opportunity to come into town, and enjoy this fascinating city.
Enjoy!