Some of the biggest stars stood up to cancer last night ... and they looked hot doing it!

Selena Gomez, Reese Witherspoon, Heidi Klum and Christina Aguilera attended the "Hollywood Stands Up to Cancer" event presented by The Entertainment Industry Foundation on Wednesday in Los Angeles.

Reese, who co-chaired the event with husband Jim Toth, looked gorgeous in a very low-cut orange dress.

And she wasn't the only one showing some decolletage though -- Gomez and Klum were happy to put the girls on display. The supermodel looked sexier than ever on her first red carpet since breaking up with bodyguard Martin Kristen.

The event was an A-list affair, with stars like Drew Barrymore, Gwyneth Paltrow, Anne Hathaway, Zooey Deschanel, Anna Kendrick and Jessica Alba all showing their support for the cause.

Jamie Foxx also showed up with his adorable daughter Annalise Bishop -- the two doing some hilarious poses together for photographers.

Foxx, Aguilera and John Mayer all performed at the event as well, with also Katy Perry showing up to support her boyfriend.

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