When my dad was diagnosed with myeloma I told him I didn't know what to say. He said there's nothing to say about it.
Rather than talk about our feelings, which my family never really did, we just continued shooting the shit and joking and sending each other the equivalent of cat pics for old people.
Despite myeloma being incurable, it's treatable and some people last a long time and you kind of cling to the hope that this case will be one of those. Despite the statistics.
When the melonomas appeared though, every conversation became incredibly weird and difficult because we both basically assumed we were just waiting for him to die, which he did quite soon.
Sorry for making this about me and again, I'm not really sure what to say to you. The death in life sucks. Not sure about your relationship with your mom is like, but I hope you can avoid my situation of being weirded out talking to each other.