Unlike most other cancers, breast cancer is not just one type. It's extremely complex, and many factors go into treatment, projected outcome, and recurrence risk. Is the cancer invasive or non-invasive (still contained)? In what part of the breast did it begin (ducts, lobules, connective tissue)? How does it appear under a microscope (there are many subtypes of each of the above)? Is it hormone-receptive (estrogen, progesterone)? What's its genetic makeup (using that information, the cancers can be grouped, and treatment better targeted)? Understanding this complexity can help explain one reason there is still no cure.
Mayo Clinic: breast cancer types - what your type means