First off, both films are about a shy brunette who falls for an elusive Mr. Grey and has S&M sex with him.
In Fifty Shades, Christian Grey wants Ana Steele to open up, which just leads to her getting flustered.
An almost identical situation happens in Secretary, but leads to a more genuine conversation.
Ana and Christian appear to have that moment of sexual discovery in an elevator.
It's fine, it's hot, whatever.
But this is that same moment in Secretary.
Fifty Shades is all about the secret sensual touching.
So is Secretary, but it gets way more subtle.
In Fifty Shades, Christian's controlling behavior primarily functions to make the sex more interesting.
But in Secretary, Edward actually maintains a level of openness with Lee that makes her feel less alone.
There's that moment where Christian shows Ana his BDSM sex chamber.
But Secretary isn't afraid to get really weird.
Also, Fifty Shades seems pretty tonally serious.
But Secretary is, at its core, a rom-com, and has some really funny bits.
Mostly though, Ana and Christian's romance (spoiler alert) doesn't ever blossom into a real, truly loving relationship.
It ends with Ana learning that she's incompatible with Christian and leaving him.