Each cancer is different. I think it's best to focus on the person with the illness and what is best for their peace of mind, quality of life and happiness. Cancer is caused by a genetic hiccup in a particular cell and this can happen randomly and is more common with increasing age. I've had breast cancer and I feel it is bad luck but not in my control. I had the best treatment available at the time, a low grade tumour which tends not to spread or kill you, and I'm here 13 years after diagnosis. Other people I met through treatment were not as lucky, although some were, some weren't.

Sometimes the primary cancer is in a part of the body which isn't easy to detect cancer in so by the time the cancer has spread from the original site, it's too late to treat the area where the cancer started. Once a cancer has "metastasised" i.e. moved from the original site, it is usually too late to stop, but not all cancers are like this. Some "terminal" cancers can be managed for a long time as a chronic illness but others are more aggressive. Some cancers that have spread can sometimes be treated with particular medication or therapy that stops it in its tracks. I'm thinking of Lance Armstrong who had testicular cancer which spread to his brain and who is still alive.

What I am trying to say is that cancer is a very variable condition, it can be easy to treat, but often it isn't. Please do your best to support your relative and not to be too sad. In many ways it's worse to be an onlooker feeling powerless to help. A kind word and a  nice cup of tea and a bit of distraction is very helpful.