• Women or men at least 18 years of age

• Pathologically documented diagnosis of measurable or evaluable metastatic breast cancer with known ER, PR, and HER2 status determined by the local laboratory on the primary tumor.

• Enrolled before or during first line of treatment for metastatic breast cancer. No more than 1 prior line of therapy in the metastatic setting.

• Accessible medical records for all treatment and response data in the metastatic setting.

• Willing and able to receive medical treatment or follow up by investigators at UNC-Chapel Hill.

• Receiving treatment for metastatic breast cancer.

• Treating physician considers patient well enough for standard of care therapy including chemotherapy.

• Willing to give blood for research purposes upon study enrollment and at first disease progression.

• Available archival primary tumor suitable for molecular analysis. If the primary is not available, willingness to obtain extra samples for research during planned standard of care biopsy, or willingness to undergo biopsy for repeat clinical receptors and molecular analyses.

• Archival metastatic sample available and suitable for molecular analysis. If not available, willingness to undergo biopsy for repeat clinical receptors and molecular analyses. If no archival metastatic sample is available and the metastasis is not amenable to biopsy per treating physician the patient may still be enrolled.

• Be willing and capable of providing informed consent, recognize the experimental nature of the trial, and sign the IRB-approved written informed consent documentations