You don't always have to talk. Much can be expressed without words. If your friend's appearance has changed, don't ignore it. Be gentle, yet remember, never lie. Encourage your friend to make decisions.
Illness can cause a loss of control over many aspects of life.
Don't deny your friend a chance to make decisions, no matter how simple or silly they may seem to you. Tell your friend what you'd like to do to help. If your friend agrees to your request, do it. Keep any promises you make. Remember, anger and frustration are often taken out on the people most loved because it's safe and will be understood.