Worst case scenario in both instances, I'm afraid, but here goes:
My father in law had bowel cancer 20 years ago and ended up having a huge chunk of his bowel removed and having a stoma (?) bag fitted. He survived for 18 months after diagnosis but in the end was just too weak to carry on.
My dad had cancer of the oesophagus 9 years ago. Chemo and radio therapy didn't have much effect, I'm afraid, and in the end the cancer just grew until he couldn't eat and he pretty much died of malnutrition, complicated by an internal bleed. He was, however, a bit daft in that he refused to rest until his illness forced him to - and then it was too late.