At a Broadway premiere, 1956
The Bowery Boys blog takes a look at Monroe movies with a Broadway connection – including All About Eve, Gentlemen Prefer Blondes, The Seven Year Itch and Bus Stop. Her most succesful film, Some Like it Hot, was later adapted for Broadway.
I would add to that list Clash by Night (based on a play by Clifford Odets), and The Prince and the Showgirl (based on a London theatrical hit by Terence Rattigan.)
Because Marilyn played a showgirl so often, you could also count There’s No Business Like Show Business and Let’s Make Love. And her last film, The Misfits, was the first screenplay by playwright husband Arthur Miller.
