Dave Coulier -- who played Uncle Joey on "Full House" -- is a 2-time cancer survivor ... and he told us the key to his success in fighting the monstrous disease.

When we caught him out in NYC today, Dave told us ... "Early detection is everything, so talk to your doctors. Get those PET scans, get those MRIs, get those CT scans, because it can save your life. I'm living proof of that."

So if you've been putting off a doctor's appointment ... Cut. It. Out!

The 66-year-old actor is now in remission from tongue cancer ... after finishing treatment for Stage 3 non-Hodgkin lymphoma in 2025.

While the journey was rough, Dave credited his sense of humor and fellow "Full House" alum, John Stamos with helping him get through his toughest days while on the road to recovery.

Watch the video to find out what Dave says is next for him after becoming cancer-free.