Adrian Grenier loves to throw his support behind good causes - and if those causes let him ogle flocks of girls in their underwear, so much the better!

We caught the Entourage star taking part in An Underwear Affair, a marathon which encouraged people to run in their skivvies in order to boost cancer awareness. Although Adrian ran the race in normal attire, he made plenty of time for his scantily-clad fans, including one cheeky young lady seen above. Good thing his girlfriend Isabel Lucas was there to keep an eye on things!