Tka Assay for CDK4/6i

This clinical trial assesses whether using a test developed by DiviTum can identify optimal levels of CDK 4/6 inhibitor medications in the blood and whether assessing medical compliance and drug-drug interactions can optimize (improve) these levels in patients with estrogen receptor (ER) or progesterone receptor (PR) positive, and human epidermal growth factor receptor 2 (HER2)-negative breast cancer that has spread from where it first started (primary site) to other places in the body (metastatic) and are receiving CDK 4/6 inhibitors. CDK4/6 inhibitors in combination with endocrine therapy (ET) is first line treatment for metastatic hormone positive (ER/PR positive) breast cancer (mBC). Thymidine kinase is a biomarker (biological molecule found in blood, other body fluids, or tissues that is a sign of a condition or disease) that reflects cell proliferation (an increase in the number of cells as a result of cell growth and cell division). DiviTum-thymidine kinase activity (TKa) is a Food and Drug Administration approved assay which showed that a TKa is associated with the decreased likelihood of disease progression within 30 days or 60 days post testing. Using the DiviTum-TKa may improve medication compliance and remove potential drug-drug interactions in patients with ER/PR positive HER2-negative MBC.

Sex

Female

Minimum age

18 Years

Inclusion Criteria:

* Participants must have histologically confirmed metastatic ER-positive (\> 10%), PR-positive or PR-negative, and HER2-negative (0 by immunohistochemistry \[IHC\] or if +1 or +2 by IHC, not amplified by fluorescence in situ hybridization \[FISH\]) breast cancer; ER positivity, PR positivity, and HER2 negativity as per the 2018 joint American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines.
* Participants must be starting CDK4/6 inhibitor and endocrine therapy as part of first-line therapy per standard of care and be previously CDK4/6 inhibitor-naïve.
* Participants must be enrolled prior to starting CDK4/6 inhibitor therapy.
* Participants must be ≥ 18 years of age.
* Participants must have an Eastern Cooperative Oncology Group (ECOG) Performance Status \< 3.
* Willing and able to provide written informed consent for the trial.

Exclusion Criteria:

* Participants without evidence of metastatic disease prior to registration.
* Participants with prior use of CDK4/6 inhibitor therapy.
* Participants who are unable to provide informed consent for the trial.