I have thought a lot about this over the last few years and although I felt what you felt from the ghosting I believe it is part of their survival instinct and not out of any sort of malice towards you. It is tough to be around sick people as it can be a real downer,
This is something most people like to avoid if possible. Not knowing what to say after the initial 'I'm sorry' can be hard. Life goes on, even when someone has cancer and I think what can be helpful to ghosters is that they are not expected to fix the illness, it is just to help that person hold on to some sort of normal life.