Ig, I am in a similar situation. I am 20 years old (also a college student) and my mother was diagnosed with cancer back in November. It is a tough situation for everyone, but definitely for the one actually affected by the cancer. The best thing to do is just be there for her and listen to her. I know my mother always wants to talk about what is going on with her. However, that is when she is ready to talk about different things. This may be hard to figure out at first, what to talk about and when, but you will learn.
When I first learned she had cancer, I was devastated. I felt like a zombie and couldn't think about anything else. It was hard to go to school and do my work. However, I did it. I knew I had to keep my head straight and keep up with my quality of work. Learning she was sick affected me more than I thought it would. I can understand your feelings.
My mother and I are close. I am the only girl in my family (have all brothers). My mom is the one that I do hockey stuff with. It has been hard not being able to do the stuff we used to, like going to games and practices. I had to realize she was tired and wasn't up to it. You will have to be understanding that your friend may not be up for the same old thing too (whether that be going out, certain conversational topics etc.) Try to remain the same friend you were. (Some people change when they find out someone is sick.) Hope this helps at least a bit.
(If you ever need to talk, feel free to im me.)