CDK and Body Composition Study

Inclusion Criteria: * Histologically confirmed adenocarcinoma of the breast that is Estrogen Receptor (ER) and/or Progesterone Receptor (PR) positive based on current American Society of Clinical Oncology-College of American Pathologists (ASCO-CAP) guidelines * Metastatic or locally advanced/inflammatory, unresectable breast cancer not amenable to potentially curative surgery * Measurable and/or non-measurable as defined by RECIST 1.1 criteria * Patients must be a candidate to start an FDA approved CDK 4/6 inhibitor (palbociclib, ribociclib, abemaciclib) as part of standard of care treatment * Female, or male patients, and age \>=18 years * Eastern Cooperative Oncology Group (ECOG) performance status 0-2 * Ability to understand and the willingness to sign a written informed consent document * Concomitant therapy with bisphosphonates, RANKL inhibitors or growth-colony-stimulating factor (G-CSF) is allowed as per physician decision Exclusion Criteria: * History of allergic reactions attributed to compounds of similar chemical or biologic composition to CDK 4/6 inhibitors or other agents used in the study (e.g., fulvestrant, letrozole, anastrozole, exemestane) * BMI \< 18.5 * Prior CDK 4/6 use in any setting * Inability to undergo anthropometric measurements * Inability to undergo CT scan imaging * Women of child-bearing potential must not be pregnant or breast feeding. They must also agree to use adequate contraception (hormonal or barrier method of birth control) and not be…