JayMatt,
thanks for your posts – very thought out and you say based on da’as torah. 2 things I think though need clarification in your third example above (boy is in remission) and I’d love to hear your take on them.
1. would this only apply to hiding the info if the other person doesn’t ask or even to lie outright even if they do ask? (Suppose they say they heard a rumor that he once had cancer and they ask you if thats true).
2. would you tell her at some point before the l’chaim so she can make a decision whether it bothers her or if she doesn’t find out before the chuppa then so be it?