UPCC 17124 Comparing Oral Drug Dosing Strategies in Older Patients with Metastatic Breast Cancer to Maximize Tolerance and Reduce Discontinuation: The CDK4/6 Inhibitor Dosing Knowledge (CDK) Study

Dosing Strategies for Older Patients with Metastatic Breast Cancer

Enrolling By Invitation
65 years or above
All
Phase 3
500 participants needed
1 Location

Brief description of study

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.

Detailed description of study

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.

Eligibility of study

You may be eligible for this study if you meet the following criteria:

  • Conditions: Metastatic Breast Cancer
  • Age: 65 years or above
  • Gender: All

Inclusion Criteria:

  1. Hormone receptor positive (HR+) HER2 negative metastatic breast cancer. Cut-off values for positive/negative staining should be as per standard practice in accordance with ASCO/CAP (American Society of Clinical Oncology/College of American Pathologists) guidelines. Verification of histology is preferred at the time of recurrence and where not possible or necessary in the judgment of the treating physician, the study will accept histology from the initial diagnosis.
  2. Candidate for planned endocrine therapy in combination with 1st use of palbociclib or ribociclib, in the metastatic setting. The planned endocrine partner can be an aromatase inhibitor (letrozole, anastrozole, exemestane) or fulvestrant, selected through patient/provider choice.
  3. Aged 65 years or older
  4. Adequate bone marrow and organ function. Laboratory values must be within normal institutional limits, or within ranges as indicated below, or demonstrate minor abnormalities that are deemed clinically non-significant by the investigator.
    • Absolute neutrophil count ≥ 1,000/µL
    • Total bilirubin ≤ 1.5 x institutional upper limit of normal (ULN) (participants with documented Gilbert's disease are allowed total bilirubin up to 5X ULN)
    • AST (SGOT)/ALT (SGPT) <3 x institutional ULN, or ≤ 5 x ULN for subjects with documented metastatic disease to the liver.
  5. Baseline QTc ≤ 480 ms (only for ribociclib patients)
  6. Ability to understand and the willingness to provide informed consent. Note: Remote consent is allowed per institutional guidelines.

Exclusion Criteria:

  1. Previous treatment with a CDK4/6 inhibitor for metastatic breast cancer, or previous treatment within the past 12 months with a CDK4/6 inhibitor in the neo/adjuvant breast cancer setting.
  2. Received greater than 30 days (in the metastatic setting) of the specific endocrine therapy agent planned as partner to the CDK4/6 inhibitor in the study at the time of randomization.
  3. Known history of intolerance or allergy to the planned agents used in this trial.
  4. Uncontrolled intercurrent illness that, as evaluated by the treating clinician, would hinder compliance with study requirements.
  5. Concurrent therapy with other investigational agents.
  6. Rapidly progressive brain metastases.
  7. Active or chronic Hepatitis B or C are eligible provided they meet liver function laboratory criteria and are not on medication with a known interaction with the study agents.
  8. Current use of drugs that have known potential to prolong the QT interval (e.g., antiarrhythmic drugs), for patients on ribociclib. Note: If concomitant use cannot be avoided, monitor ECG when initiating, during concomitant use, and as clinically indicated. Refer to crediblemeds.org as a resource.
  9. Prior or concurrent malignancies that are undergoing active treatment.

This study investigates different dosing strategies for CDK4/6 inhibitors in older patients with metastatic breast cancer (MBC). The purpose of the study is to compare standard dosing with a titrated dosing approach to see which helps patients tolerate the medication better and continue treatment longer.

Participants will be randomly assigned to one of two study arms: one receiving the standard dosing and the other receiving a titrated dosing that starts at a lower dose and increases if tolerated. Participants will choose, with their doctor, which CDK4/6 inhibitor and endocrine therapy they will use. The study will assess how long patients stay on the treatment and how they handle the side effects.

  • Who can participate: Participants must be aged 65 years or older with hormone receptor positive, HER2 negative metastatic breast cancer. They should have adequate bone marrow and organ function and be candidates for planned endocrine therapy with palbociclib or ribociclib.
  • Study details: Participants will be randomly assigned to receive either the standard or titrated dosing of a CDK4/6 inhibitor, in combination with an endocrine therapy of their choice. A placebo is not used in this study.
Updated on 29 Jun 2026. Study ID: 24-2037
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