What to do

My son has a good friend that he has been hanging around with for about 6 years. His parents are divorced. He lives with his mother. Since I have known him he has lived in about ten different places. A little over a year ago his mother found out she had cancer. This weekend he told my son they gave her 4 months.  He is a good kid. To talk to him you would never know that his home life was not an ideal one.  I don't even know where to go with this. I feel helpless in every way. He stays with us a lot and knows he is always welcome. We have told my son he can live with us if he needs or wants to. But, other than that, I remain clueless as to what we can do to help him.