I had to go with "No", just based on my own situation. My family has a horrible tendency to run wild with rumors because they are somehow afraid of offending someone by asking them a question directly or something. So when I was diagnosed with MS, I made sure I personally told people that I had it, that I was taking care of myself, AND told them to come to me directly with any questions or fears rather than going to the internet or, worse yet, my mother. I also think too many people "hide" a disease like MS until or unless they have noticeable problems, which can make it really frightening for people who are newly diagnosed and are only aware of people who have it that are wheelchair bound or have other severe problems. I had a distant cousin who was diagnosed with it that killed himself because he thought he was going to die anyway. I'm "fine" and I am certain I am not going to die an early death because of this disease and I think my family is less concerned about it because they aren't feeding off of rumors and horror stories. It's much easier for me to be open than to hide it.
If it were cancer, I'm not sure how I would handle it. Probably the same way. It's hard enough to deal with a disease, I don't need to add the stress of keeping secrets too it!