DiviTum®TKa: A Biomarker Assay for Efficacy in HR+ Breast Cancer Patients

Inclusion Criteria:

* Pre- or post-menopausal HR+ metastatic breast cancer patients who are:

  * Group 1: scheduled to initiate 1st line combination therapy with an FDA-approved CDK4/6 inhibitor (palbociclib, ribociclib, or abemaciclib) and an FDA-approved endocrine therapy for pre- or post-menopausal HR+ metastatic breast cancer (mBC).
  * Group 2: scheduled to initiate second or later lines of therapy with an FDA-approved CDK4/6 inhibitor (palbociclib, ribociclib, or abemaciclib) with or without an FDA-approved endocrine therapy for pre- or post-menopausal HR+ mBC.
  * Group 3: currently receiving 1st line therapy with an FDA-approved CDK4/6 inhibitor (palbociclib, ribociclib, or abemaciclib) and an FDA-approved endocrine therapy for pre- or post-menopausal HR+ mBC.
  * Group 4: scheduled to initiate, or are currently receiving, 1st or 2nd line therapy of an FDA approved endocrine therapy (single agent) for pre- or post-menopausal HR+ mBC.
  * Group 5: scheduled to initiate or are currently receiving 1st line therapy of an FDA-approved CDK4/6 inhibitor (ribociclib or abemaciclib) with an FDA approved endocrine therapy for stage 2 or stage 3 adjuvant HR+ BC

NOTE: Patients that meet eligibility criteria for any of the above groups that are already enrolled in an ongoing clinical trial are eligible for co-enrollment to this observational study.

Exclusion Criteria:

* Treatment including investigational agent or therapies
* Early breast cancer diagnosis
* Male breast cancer
* Currently receiving treatment for other active malignancy at time of registration

  * EXCEPTIONS: Nonmelanoma skin cancer or carcinoma-in-situ (e.g. of cervix, prostate)
* Inability to give written informed consent