Sugar is a basic nutrient. You feed cancer with the same things that feed your body because cancer IS your body, just malfunctioning. If you want to change anything about your diet related to cancer, it's to cut out carcinogens to prevent it. Eating matters more if you start getting chemo and have to eat well to withstand it.
The best choice is medicine. Like, actual medicine. Which is hard to get, especially for the OP. CBD can do something, better than smokin weed too since that aint great for the lungs. But that'll just delay it until OP can get real drugs.
Best of luck, OP.