Use of DiviTum TKa for Treatment Monitoring in Patients with Hormone Receptor Positive HER2 Negative Metastatic, Advanced, or Unresectable Breast Cancer Receiving CDK 4/6 Inhibitors, the TK IMPACT Study

Inclusion Criteria

• Diagnosis of metastatic or advanced unresectable invasive breast cancer that is hormone receptor-positive (HR+) and HER2-negative. Tumor assessment by radiographic imaging will be performed within 4 weeks of baseline study visit
• Cohort 1 only: Scheduled to initiate standard of care first-line therapy with any Food and Drug Administration (FDA)-approved endocrine therapy plus any FDA-approved CDK 4/6 inhibitor (palbociclib, ribociclib, or abemaciclib) for the stated diagnosis at the time of study enrollment. Type of endocrine therapy and CDK 4/6 inhibitor will be documented
• Cohort 2 only: Currently receiving first-line therapy with any FDA-approved endocrine therapy plus any FDA-approved CDK 4/6 inhibitor (palbociclib, ribociclib, or abemaciclib) for no longer than 24 months with at least stable disease (no progression) on such therapy for a minimum of 12 weeks prior to enrollment as determined by radiographic studies as deemed appropriate by the treating physician. Type of endocrine therapy and CDK 4/6 inhibitor will be documented
• Any prior therapy for early stage breast cancer is allowed, including endocrine therapy and chemotherapy
• Cohorts 1 and 2: Prior receipt of adjuvant CDK 4/6 inhibitor therapy is permitted provided therapy completion occurred > 12 months prior to study enrollment
• At least 18 years of age
• Life expectancy > 6 months
• Post-menopausal status, defined as one of the following: * Age >= 60 years * Age < 60 with intact uterus and amenorrhea for 12 consecutive months or more * Status post bilateral oophorectomy, total hysterectomy * Pre- or peri-menopausal with suppressed ovarian function by use of GnRH agonist/antagonist or surgical bilateral oophorectomy
• Ability to understand and willingness to sign an Institutional Review Board (IRB) approved written informed consent document (or that of legally authorized representative, if applicable)
• Currently being treated at Siteman Cancer Center by a medical oncologist participating in this trial
• PHYSICIANS: Medical Oncologist at Siteman Cancer Center
• PHYSICIANS: Treating patients with metastatic or advanced unresectable invasive breast cancer
• PHYSICIANS: Willing to complete Study Care Plans on a serial basis during participation

Exclusion Criteria

• Receipt of any prior cytotoxic chemotherapy line for metastatic disease. There will be no limit to chemotherapy use in the neoadjuvant or adjuvant setting
• A history of other malignancy with the exception of malignancies for which all treatment was completed at least 2 years before registration and the patient has no evidence of disease
• Concurrent participation in any investigational therapeutic trial for treatment of metastatic breast cancer