This is so interesting. When I was dx in 2010 I had the full range of treatment, chemo, surgery, rads and Herceptin. My onc told me straight, that after Herceptin for the HER2+ status having radiotherapy was the best chance of it not recurring in the future.
I know there are no guarantees but I definitely think that radiotherapy is sometimes the unsung hero and gets a little forgotten with credit going to other more "sexy" treatments.