This clinical trial is for adults who have metastatic breast cancer with a BRCA 1 or BRCA 2 mutation of the tumor detectable by blood or tumor tissue.
   
The purpose of this study is to evaluate the effectiveness of an experimental study drug called talazoparib as a potential treatment for metastatic breast cancer with a BRCA 1 or BRCA 2 mutation of the tumor detectable by blood or tumor tissue. The U.S. Food and Drug Administration (FDA) has not approved talazoparib for this specific disease, but it has been approved for metastatic breast cancer with an inherited BRCA mutation.
   
Talazoparib is a study drug that inhibits (stops) the normal activity of certain proteins called “poly (ADPribose) polymerases” also called “PARPs”. PARPs are proteins (made from genes which are part of your DNA) that are found in all normal and cancer cells that are involved in the repair of DNA. 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 cancer cells. Cancer cells may be killed by a study drug, like talazoparib, that stops the normal activity of PARPs. In clinical trials, the use of talazoparib and other PARP inhibitors have shown that these drugs can reduce tumor size and slow tumor growth in some cancer patients with BRCA1 or BRCA2 mutations.
   
Talazoparib is given orally. Each study drug cycle lasts 4 weeks during which time participants will be taking the study drug once per day. The research study procedures include screening for eligibility, evaluations (blood tests, physical exam, imaging scans, etc.), and follow up visits.

Participants will receive the study drug until their disease progresses or they experience any unacceptable side effects. Participants will be followed for up to two years after their last visit.