• All subjects must be capable of providing informed consent

• Subjects (≥ 18 years of age) must have had a prior primary breast cancer diagnosis of any subtype at least six (6) months before presentation with suspected metastases or be presenting with de novo metastasis. o Patients on adjuvant treatment for primary disease are eligible provided clinical progression (suspected recurrence) is evident based on radiological assessment

• Subjects must have suspected recurrent metastatic BC or MBC with clinical signs of progression that will be confirmed/evaluated by tissue biopsy that is expected to yield tissue adequate for histologic examination. Note that patients presenting with de novo metastasis are eligible provided a tissue biopsy meets the above criteria.

• Tissue biopsy of a suspected metastatic lesion must be taken prior to treatment for metastatic disease and can be either: (i) after liquid biopsy blood draw for this study, or (ii) at least one week prior to liquid biopsy blood draw for this study.

• The suspected metastases biopsied may be from any lesion outside the ipsilateral breast and axilla, infra/supraclavicular areas.

• In those with suspected metastases in contralateral axilla, infra/supraclavicular areas, only a new contralateral breast primary must be excluded by imaging.

• No history of any other cancers (except for non-melanoma skin cancer)

• Ability to access 3-month outcome data (de-identified, consented patients included for second draw at 3-month timepoint or within 14 days for the first post-treatment imaging, whichever comes first).

• Data from contemporaneous diagnosis (metastatic recurrence or de novo) and in applicable past diagnosis (primary) must be accessible, including a pathology report that details standard markers and morphology describing how malignancy/cancer of origin was determined.

• Capable of providing informed consent

• Subjects (≥ 18 years of age) must have had a prior primary breast cancer diagnosis of any subtype at least six (6) months before presentation with suspected metastases or be presenting with de novo metastasis.

• Patients on adjuvant treatment for primary disease are eligible provided clinical progression (suspected recurrence) is evident based on radiological assessment

• The suspected metastasis biopsied may be from any lesion outside the ipsilateral breast and axilla, infra/supraclavicular areas.

• In those with suspected metastases in contralateral axilla, infra/supraclavicular areas only, a new contralateral breast primary must be excluded by imaging.

• Confirmation of progression of MBC must be confirmed by imaging

• (Optional) Tissue biopsy of suspected metastatic lesion must be taken prior to treatment for metastatic disease and can be either: (i) after liquid biopsy blood draw for this study, or (ii) at least one week prior to liquid biopsy blood draw for this study.

• No history of any other cancers (except for non-melanoma skin cancer)

• Data from primary BCa diagnosis must be accessible, including detailed description with standard markers and morphology describing how malignancy/cancer of origin was determined.

• Subject must exhibit clinical signs of breast cancer recurrence or progression of previously confirmed metastatic breast cancer