This phase II trial studies how well talazoparib works for the treatment of breast cancer with a BRCA 1 or BRCA 2 gene mutation that has spread to other places in the body (metastatic). Talazoparib is a study drug that inhibits (stops) the normal activity of certain proteins called poly (ADP-ribose) polymerases also called PARPs. PARPs are proteins that help repair deoxyribonucleic acid (DNA) mutations. PARP inhibitors, such as talazoparib, can keep PARP from working, so tumor cells can't repair themselves, and they may stop growing. PARPs are needed to repair mistakes that can happen in DNA when cells divide. If the mistakes are not repaired, the defective cell will usually die and be replaced. Cells with mistakes in their DNA that do not die can become tumor cells. Tumor cells may be killed by a study drug, like talazoparib, that stops the normal activity of PARPs. Talazoparib may be effective in the treatment of metastatic breast cancer with BRCA1 or BRCA2 mutations.

This phase III trial compares the effect of radiation therapy combined with hormonal therapy versus hormonal therapy alone in treating patients with low risk, early stage breast cancer with Oncotype Dx Recurrence =< 18. Oncotype DX is a laboratory test which results in a score that is used to help predict whether breast cancer will spread to other parts of the body or come back. Radiation therapy uses high doses of radiation to kill cancer cells and shrink tumors but may result in some side effects. Hormones called estrogen and progesterone may contribute to the growth of breast tumor cells. Hormone therapy, also called endocrine therapy, may stop the growth of tumor cells by blocking or removing these hormones. This clinical trial may help researchers understand if patients with low-risk, early stage breast cancer who have Oncotype recurrence score of =< 18 can safely omit radiation therapy and only be treated with hormonal therapy without losing any radiation treatment benefit.