I heard this while getting ready for work this morning. He just announced his illness in April, so I'm thinking that he and ABC must have known for some time before he went off the air. You can function with cancer for a little while before it becomes major. Of course, he must not have started his treatments yet because he still looked healthy when he made the announcement.
For anyone who knows Jim Kelly (former quarterback for the Buffalo Bills - back when they were good), his son Hunter finally passed away this weekend too. That's very sad for Buffalo. He and his dad have been heroes here.