What are my chances of cin 3 becoming invasive cancer?

Too high: As far as you need be concerned, if you neglect a CIN3 lesion, just assume it will kill you -- and it won't be pleasant. Nobody knows the exact percentage that progress because anyone who values their life gets it treated. But it's high -- old studies show at least 50%. If it was a tooth, you'd have it fixed. And this time, we're talking about your life.