Inclusion Criteria:

• Invasive breast cancer with radiographic and/or clinical evidence of advanced metastatic or unresectable disease 2 ER+/HER2- patients prior to starting 2nd line therapy or beyond in the metastatic setting OR ER/PR/HER2-negative (Triple Negative) patients prior to starting any line of therapy in the metastatic setting.
• Note: ER/PR/HER2 status is defined per the 2018 ASCO/CAP guidelines as follows: ER-positive and PR-positive is defined as ≥ 1% reactive cells by immunohistochemical staining. HER2 Negative Disease is defined by meeting one of the following criteria:
  • 0 or 1+ by IHC and not amplified by ISH;
  • 0 or 1+ by IHC and ISH not done;
  • 2+ by IHC and ISH results are:
    • < 6.0 HER2 signals/cell with HER2/CEP17 ratio < 2.0;
  • IHC not done and not amplified by ISH.
• Measurable and/or non-measurable disease is allowed.
• Male or female breast cancer is allowed.
• Age > 18 years.
• Willingness to provide mandatory blood specimens.
• Willing to return to enrolling institution for follow up imaging at least once.

Exclusion Criteria:

• Life expectancy of ≤ 6 months.
• Inability to provide blood samples based on the judgment of the treating provider.

Eligibility last updated 12/20/23. Questions regarding updates should be directed to the study team contact.