rust on inside of roof?

So I've got rust perforating through, on the inside. All paint intact, all seams caulked and look factory. No rust above on outside. Apparently the windows need to be left cracked when we're hot and humid? :banghead:

So can I fix this w/o taking it all down to bare metal, and if I don't how long before I have cancer?

There are some products that supposedly bind with the rust and stop it. The easiest and surest way is to sand to bare metal, prime, then paint.
FWIW
YMMV