My son says he IS cancer

Cancer is the worst. Not just for the person who has it but for the family too. My 15 year old is fighting cancer and is going through chemo and he's been so angry lately. He has honestly been wanting to stop chemo and just die and that hurts so much. He lashes out on his sister for a really dumb reason. He asked to watch something else on TV and she said ok. That made him mad and he starts yell at her. I asked why he's yelling when she's letting him watch something else. He said if he didn't have cancer she wouldn't have changed it. He said he basically tired of being treated differently and getting all the cancer perks. He said he doesn't have cancer, he IS cancer and whenever people look at him all they see is cancer and he isn't Andrew anymore. He's just cancer. I tried to comfort him and tell him if course he's still Andrew but he pushed me away and said I always look at him like he's gonna drop dead any moment and freak out if he coughs. He took off his beanie and yelled "Andrew had hair! I don't have hair! All I am is cancer!" He is now even more persistent about stopping chemo all together. I'm trying to hold myself together. For him. His sister started crying because she felt like she did something wrong. I want to explain to her he's not mad at her, he's mad at cancer.... And I'm mad at cancer too