Is it appropriate to ask someone what kind of cancer they have?

Is it appropriate to ask someone what kind of cancer they have?

Carly Schwartz (Co-Founder) gives expert video advice on: What should I not say to someone with cancer?; Is it appropriate to ask someone what kind of cancer they have?; Is there any one thing I can say to someone with cancer to make them feel better? and more...

I think that what kind of cancer they have is private. I don't know. I don't think I would ask what type of cancer they had been diagnosed with.