Question: what to say to someone who is losing someone to cancer?
Answer: “I'm not sure exactly what to say, but I want you to know I care.”
“You are in my thoughts/prayers.”
“Can I bring you a dinner this week? ... 
“If you want to talk about him/her, please feel free to call (or text) anytime.”
“If you need me, I'll be there. ... 
“My favorite memory with (____) is…”