This phase II trial tests how well neratinib prior to the primary treatment (neoadjuvant) works in treating patients with stage I-III HER2 mutated lobular breast cancers. Neratinib is in a class of medications called kinase inhibitors. It works by blocking the action of an abnormal protein that signals cancer cells to multiply. This helps slow or stop the spread of cancer cells. Giving neratinib in addition to normal therapy may work better in treating cancer than the endocrine therapy patients would normally receive.

This phase III trial compares the effectiveness of fractionated stereotactic radiosurgery (FSRS) to usual care stereotactic radiosurgery (SRS) in treating patients with cancer that has spread from where it first started to the brain. Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. FSRS delivers a high dose of radiation to the tumor over 3 treatments. SRS is a type of external radiation therapy that uses special equipment to position the patient and precisely give a single large dose of radiation to a tumor. FSRS may be more effective compared to SRS in treating patients with cancer that has spread to the brain.