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.
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Proportion of patients with thymidine kinase activity (TKa) values that switch from profile 3 to profile 1 or 2 after medication compliance and drug-drug interaction assessment
Timeframe: Immediately following counseling for medication compliance and adjustment of potential deleterious drug-drug interactions
Rate of improvement in CDK4/6 inhibitor response (i.e. moving from profile 3 to profiles 1 or 2)
Timeframe: At day 28 of cycles 2 and 3 immediately following counselling for medication compliance and removing potential deleterious drug-drug interactions