Nginx as reverse Proxy, remove X-Frame-Options header

[basti]

Hello,

I have a closed-source Webapp that run on an IIS-Webserver and send a
"X-Frame-Options: SAMEORIGIN" header.
I also have to implement this Webapp in my own, Frame based Application.

So I try to use nginx as a reverse Proxy, but the X-Frame-Options Header
is still send.
How can I remove his header?
I have try "proxy_hide_header X-Frame-Options;" without success.

Regards,
Basti