I (28F) may have detected a cancerous lump on a guy (25M) I hooked up with.

I went clubbing downtown and met a bouncer and went home with him. I'm a resident cardiologist and diagnosing cancer is outside my specialty. However, I went to med school and I'm pretty sure I felt a lump on his testicle which seemed like it might be cancer.

I told him "This might be cancer. I'm a doctor."

He said "Uh huh. Right. What's your favorite position?"

I didn't want to ruin the hookup so I didn't say anything at first, and then I forgot about it. We didn't exchange numbers, or anything. The problem is I don't think he took me seriously or even believed that I am in fact a doctor.

I think it's something he really needs looked at. It's awkward because he never came to me looking for a medical opinion, yet I feel that I need to tell him that the lump is something to take seriously.

Do I go back to the club to try and talk to him again? How do I start the conversation? What should I advise him to do if he doesn't have health insurance?

TL;DR! - I just met him at a club where he's a bouncer and had a one night stand with him and he didn't take me seriously when I told him I was a doctor. How do I convince him to get it checked out?