The CDK4/6 Inhibitor Dosing Knowledge (CDK) Study

Overview

The purpose of this study is to generate evidence on an alternative dosing strategy for CDK4/6 inhibitors to help more patients with Metastatic Breast Cancer (MBC) (age ≥ 65 years) tolerate side effects and stay on treatment longer, to derive the most clinical benefit from these drugs. The primary objective of the CDK Study is to compare time to treatment discontinuation (TTD) on the approved dosing for palbociclib (125 mg orally daily on days 1-21 of 28-day cycle) or ribociclib (600 mg orally daily on days 1-21 of 28-day cycle) vs. TTD using titrated dosing approach with the same schedule but starting at a lower dose of palbociclib (100 mg or 75 mg) or ribociclib (400 mg or 200 mg) and escalating the dose if well-tolerated in combination with provider/patient choice endocrine therapy (aromatase inhibitor (AI) or fulvestrant) in patients age 65 or older with HR+/HER2- MBC. The secondary and exploratory objectives will generate evidence needed to personalize treatment decisions by comparing patient-centric secondary outcomes and evaluating baseline factors. Together with their treating physician, participants will choose the CDK4/6 inhibitor (palbociclib or ribociclib) and which endocrine therapy (aromatase inhibitor or fulvestrant) of their choice but will be randomized to either Arm 1 (indicated dosing) or Arm 2 (titrated dosing). Note: Telehealth visits are allowed at any time per institutional guidelines. In addition, the study allows for remote consenting per institutional guidelines.

The CDK4/6 Inhibitor Dosing Knowledge Study (CDK Study) will study CDK4/6 inhibitor dosing regimens in patients 65 or older with Metastatic Breast Cancer (MBC). The overarching goal of this pragmatic, randomized trial is to compare an "indicated" dosing approach, as listed on the FDA-approved drug label, that starts at the full dose of a CDK4/6 inhibitor (palbociclib or ribociclib) with dose reduction based on tolerability versus a "titrated" dosing approach that starts at a lower dose of a CDK4/6 inhibitor and then titrates up to full dose as tolerated. CDK4/6 inhibitors will be given in combination with endocrine therapy (either an aromatase inhibitor (AI) or fulvestrant) based on the choice of the treating clinician. The primary endpoint will be time to treatment discontinuation (TTD), defined as the time from randomization to last dose of the CDK4/6 inhibitor. The hypothesis is that starting low and escalating as tolerated will help older patients (\> 65 years) stay on therapy longer. Eligibility criteria are broad to allow patients who are not typically included in clinical trials to participate, allowing for a more representative sample of participants. The investigators will conduct sub-group analyses based on age (65-74 years vs. ≥75 years) and baseline frailty scores. This study builds upon the lessons learned from prior studies with CDK4/6 inhibitors. The investigators will augment the standard assessment of treatment toxicities assessed by the health care team with prospectively collected patient-reported outcomes data to better reflect how participants tolerate the different dosing approaches.