I've name changed and I'm not going to say my role in this issue, I just want opinions, because there have been various responses in my workplace.
If a colleague was diagnosed with cancer (treatable, good prognosis and they're not actively physically unwell) would you expect them to go off sick immediately and return after treatment/recovery or take a few days/a week to come to terms with the diagnosis, tell family etc. and then return to work until treatment starts? With paid time off for appointments as needed.
If treatment is in several phases, would you expect them (if well enough) to return to work in between or to stay off until it's all done?