Questions about my brothers physical health.

I have a younger brother who's not well, a bit of back story first. He moved out of the house a while ago to move in with his girlfriend and for the last few months my mother kept commenting that whenever she saw him he didn't look well and had lost a lot of weight (he's always been skinny). We chalked it up to stress from work and not eating properly he had been fairly ill but nothing too serious.

Last night he rang my mother telling her that the doctor had called him saying he needs to come in for a bladder biopsy since they found some irregular proteins in his bladder, he also needs some test done on his heart (I'm not sure on the specific details of the latter issue.) My brother is only 19 and although I know cancer in that age bracket is rare it is possible, I'm hoping it's not.

What I'm hear to ask is if theres anything else it could be (I'm sure there is but which would be the most likely suspect and how life threatening (if at all)it would be). Any help would be great as I have very little medical knowledge of my own, I just want to hear some facts so I can have a better idea of what we could be dealing with here.

Thanks for your time.