Jimi,

Personally, situations like this offend me. Whether or not others were joking doesn't really matter to me. If that co-worker were there, chances are that she'd be feeling pretty low and hurt. That's just not cool, imo.

I would remind them that we all have problems and they probably wouldn't be real keen on others teasing them if (or when) they'd go back in for serious treatment. They may think that you're being a "fuddy duddy", but I'd venture to say that a couple of them probably feel the same way & they're just holding their discomfort in to themselves.