You never want to get too invested in pursuing one medical specialty, since you haven't even begun medical school yet. However, you seem to have a lot of experience in that particular field, and having a interest in a particular side of medicine is a good way to keep up the steam through all your classes. Your extensive research is great, your shadowing is probably more than enough and you seem to have a good start on your clinical exposure. Do whatever you want with cancer research. However, you need to have some kind of volunteer work which shows your altruism. That is very important and can be clinical or non clinical. Since you seem to have lots (or will soon) of the former, I recommend getting involved with a service group on campus, tutoring or some other community volunteer group. Looks great, otherwise. Good luck!