It depends if you are considering ‘major’ from a surgical point of view. I would think a straightforward mastectomy was not as major as a full leg amputation, for example. Just more things to consider, to possibly go wrong and the impact on the patient is usually much greater. But if you are considering the hoped for impact of your story in the media, it’s huge!! A Royal loses a breast! Who’da thought. Never look to the media for even handed reporting!
But SF’s decision to make it public is a good thing. She just might prompt people to have a check up. That’s when being a major influencer matters more than major surgery.