Most of my weight was put on from a lot of comfort eating when my father died two years ago. I found myself ordering so many takeaways because I didn't want to run into people who knew me while shopping, and sometimes I couldn't bear the thought of cooking, so I would eat a packet of crisps from a 10-pack all day long to stive off the hunger! Most nights I couldn't sleep, so I ended up drinking mountains of Coke and piled on about 3 stone!
I was in denial about my weight for a very long time, and made some small attempts to try and lose it over the course of the year I admitted I had a problem. But sitting down and thinking to myself that my dad's condition was hereditary, congenital (I could have been born with this) and could be triggered by a diet high in fat led me to suck it up and do everything I could to make sure that bad lifestyle choices wouldn't leave my fiance in a state of depression with our future children and no mummy to take care of them.
Like with your case, cancer is known to run in families, so tell yourself you need to do everything possible to make sure your children don't end up going through the same thing you are now. Trust me, the junk food does not help you feel better. In fact, the lack of nutrients will probably lead to you feeling even more run down and depressed, which in turn will likely make you eat even more junk food! Try to make the change now - get plenty of fruit and veg into you, take some supplements, maybe make a huge pot of home-made soup, which should last you about 4 days in the fridge, drink lots of fluids and you'll feel far better (trust me). It will also give you the energy you need to tackle the days ahead.
Very best of luck to you and your dad x