I had that happen to me. And I found it very annoying. I understood the reason (low white cell count) but was not pleased with the way it came about. Nobody told me there was a problem until after I took the day off work, was sitting in the chemo chair, and the nurse came up and said I was already cancelled. I was even less happy when I was told by the lab that they couldn't let me see my lab results directly because of privacy laws!? How does privacy prevent them from telling me my own results?
There is a tendency in the medical community to assume that all patients have unlimited time on their hands. I certainly understand that treatment is important, but so is work and family. I actually had a person in a medical office tell me this week that of course I could get to an appointment at a very disruptive time because the law required my employer to let me go. I doubt that law applies to an employer with as few employees as the place where I work. I have to work with my employer, not against him.
And now I'm venting. :-)