In how many years does it take to become an oncologist nurse?

Well you first have to become a nurse. That's two years of pre-requisites(basic science, anatomy, english,etc.). And then two years of nursing school. Then once you've taken your boards and become licensed (you can work) and spend another two years specializing in oncology (kind of how doctors have residency when they specialize in a specific area). So I would say 6 years.