Confused - unsure why Mum might not be able to have treatment if she has two different cancers

It looks like my mum has a tumour on her kidney and on her lung. She went to see urology a couple of weeks ago and he said that they could treat with immunotherapy and he referred her to an oncologist that she is yet to see. Today she went and seen respiratory and he told her that  if the cancer in her lung is the same as her kidney that it would be easier to treat but if she has two different types of cancer it would be difficult and they might not be able to do anything?? I’m a bit confused as to why they would say nothing can be done. If anyone has any advice I would appreciate it. She has a biopsy on her lung on Thursday.