My history is borderline regular smear > biopsy (low grade CIN) > Lletz > Diagnosis
I was lucky, my cancer started high up and had just started to grow down at the point I had my smear. Otherwise it could have been another 3 years before it was discovered. It was found as soon as it would have been detectable on a smear. Because it was higher up it was only when the consultant started the lletz and removed cells further up that she had an inkling something was wrong. She didn't tell me then, but waited for the results, which she fast-tracked. I had a phone call on a Fri pm asking me to urgently go in Monday am (and take someone with me). So I feared the worst, but didn't actually expect it. There was a Macmillan nurse there and as soon as I entered the room I could see the sympathy on their faces.
I had been reassured all the way through that it looked fine and there was nothing to worry about :(
However, I know my case was very unusual.... there are others who have severe CIN 3 and everything turns out fine. You can never tell!