My mother treatment for her throat cancer and has recently been given results from her first follow-up CT and PET scan: no detectable trace of cancer in its previous location.
(Pause for cheers)

We are all thrilled with this news.... but I have questions I am not comfortable asking her.

I am guessing these results came from the scans and oral examinations.
When recurrance happens, is that a regrowth of cancer cells? Or is it that the cancer was never 100% removed and - over time - grows to a detectable size?

I guess a follow up question is about rate of recurrence and probability. If she was told, 'no trace of cancer where it was,' what are the probable outcomes?
1) cancer stays away
2) cancer 'returns' - how quickly is this possible? within the three months between now and her next visit?
3) Her doctors warned that recurrence is most likely within 2 years. I guess after 5 years, cancer is considered cured.

I do appreciate her wonderful news, but I would also like to know the possibilities to look out for.
Thank you in advance.