Others can comment as well and I am not a medical professional but as I understand it there are many forms of leukaemia acute or chronic some that require chemo treatment, periods of remission , followed by more chemo treatment and so on repeated until at some point someone might have a stem cell transplant . For some forms people have a daily pill regime alongside any other treatment.
So having said all above it really would I guess be dependant on what variation of the disease you have whether acute or chronic and treatment history to date whether it would be considered an excessive demand to take over any treatment regime. The pharmaceutical option for some forms of leukaemia can be extremely expensive for example well in excess of the annual limit.
Some forms of leukaemia also have a watch and wait phase where no treatment may be required for years.
As said I am not a medical professional so above just my own thoughts based on family experience with this disease so I would not like to speculate one way or other if would be an immigration issue
