I lived with 5 boys when I was diagnosed with breast cancer. My youngest just turning 12. One way boys cope is to ignore. It is often easier to pretend awful experiences don’t exist.
Here is a solution. The “pillow journal.” Use an inexpensive school notebook or an artist notebook or journal. Begin a journal entry telling your child you want to talk with them about cancer, but since this subject may be too hard to discuss in person, you both can use this journal to talk to each other as much as you want; about thoughts and fears.
Leave it on their pillow and ask them to place it back on yours when they write in it. You may only be the one writing for awhile. But don’t give up. At least you are acknowledging them and their fears. They may act tough, but they are frightened too.