Nginx: disable caching if page contains the word

I am using nginx as a reverse proxy.

Is it possible somehow to access response page content as a variable to disable caching for a pages that have specific word in content (not in header) WITHOUT modifying backend?

Any way would be appreciated including inline perl, lua or even piping page content to php script that would parse the content.

I can even make a dirty code hack if someone could show me a source file which parses page response and any idea what I can change in that file (add no cache headers or just hack some other variable that corresponds caching)