We have read on here many times of people who have been refused a Medical Certificate following childhood problems which have not recurred. I know you are supposed to declare them but one has to use a certain amount of discretion.
Having not suffered from this since you were 4 years old, and having been discharged, I would be very careful saying anything to anybody.
Also, being a cancer, I assume you are extremely unlikely to suffer any sudden incapacitation.
So having already declared this to an AME I would be very careful using the same AME again. You may well live to regret it.