With a cancer diagnosis, that means there is presence of cancer. It does not mean that a part of the body is 100% cancerous. With the HIPAA laws, it's true
that you will not find additional information from the care providers, but you should try to glean the information from your brother first. Is he not sharing because he doesn't know himself, he is in denial, he is afraid to share to upset you, or he just doesn't want you to know? Try to find out the cause so you can be of help. After all, this should be the ONLY reason that you know of his cancer condition. If he knows but choses not to tell you, you must try to respect that and give him the time and space that he needs. Lung cancer's mortality rate is high, and he is likely just coming to grips with that.