Hi!
I took the CPON (Certified Pediatric Oncology Nurse) exam last year. I believe the the same requirements are in place for the adult- You need to be an RN for at least 2 years and 2 years of Oncology experience. I had only been an RN for 3 years when I took the test.
It was HARD but my test had alot of growth and development as well as late effects that you probably won't get if you take the adult test.
It was MUCH harder than the boards but it was made easier by a review class and we formed study groups. It's about $300 to take but usually your hospital will pay for it. I started studyinbg about 3 months before I took it. You know, it was the one of the best things I ever did- the knowledge has really increased my ability to do teaching to the families.
Good Luck!