Truly NO one knows if they are cancer "free" at any time.
The only thing we can be resonably sure of is when we have a diagnosis of cancer because it is seen.
I usually respond with "as far as my Dr. knows" "my Dr. thinks so" or "I sure hope so". when asked these questions. I think that conveys some of the stress/joy we live with.
I don't like to be too optimistic either, just in case I need their support again.
Finally, I think we need to talk about all this superstition! I still have a 2 1/2 year old stack of thank-you notes that I cannot bring myself to mail! I do not dare to tell them anything like "cured" it's like asking the Fates to jump in and mess me up again. Emily Post is spinning right now because of it.