For me, if I tell anyone, I have to tell everyone. If one brother knows, they all have to know. Then, if my family knows, I have to tell DH's family. By that time, they have told people and the entire community knows. I really don't need everyone in my life knowing my business.
From that point, I'd spend my days fielding calls and emails from people who genuinely mean well.
No thanks...I'd rather live my life as normal as possible while being treated. If my illness is going to directly effect the lives of others, then I would consider telling them. Otherwise, its my secret to keep.
ETA: DH and I both have large families. There's no way to share news with 40 people and still keep it "personal". It won't happen.
The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing. ~Albert Einstein