Nurses who care for cancer patients can be a 2 or 4 year degreed Registered Nurse. I would recommend that you get a 4 year degree.
If you want to specialize and deal only with cancer patients you will need an advanced degree as an Advanced Practice Nurses or an Oncology Certified Nurse. You will need to take additional education and certification for either of these fields. I would also like you to tour hospitals like Mayo, who hire staff that specialize in cancer treatments.