This research study is studying a combination of HER2-directed therapies (trastuzumab and pertuzumab) and hormonal therapy as a treatment after surgery for hormone receptor positive breast cancer.

The study drugs involved in this study are:

* A combination of trastuzumab and pertuzumab given as an injection under the skin (PHESGO)
* Hormonal (endocrine) Treatment

This Phase III Trial evaluates whether breast conservation surgery and endocrine therapy results in a non-inferior rate of invasive or non-invasive ipsilateral breast tumor recurrence (IBTR) compared to breast conservation with breast radiation and endocrine therapy.