Research table: CDK4/6 inhibitors for early breast cancer treatment

This summary table contains detailed information about research studies. Summary tables are a useful way to look at the science behind many breast cancer guidelines and recommendations. However, to get the most out of the tables, it’s important to understand some key concepts. Learn how to read a research table.

Introduction: CDK4/6 inhibitors are drugs that target enzymes called CDK4 and CDK6. These enzymes are important in cell division. CDK4/6 inhibitors are designed to interrupt the growth of cancer cells.

CDK4/6 inhibitors include:

  • Abemaciclib (Verzenio)
  • Palbociclib (Ibrance)
  • Ribociclib (Kisqali)

Abemaciclib is the only one currently FDA-approved for the treatment of early breast cancer.
Abemaciclib in combination with hormone therapy is used to treat early breast cancers that are all of the following:

For people with these tumors, abemaciclib in combination with hormone therapy may reduce the risk of breast cancer recurrence better than hormone therapy alone.

Learn about abemaciclib and early breast cancer treatment, including side effects.

Learn about CDK4/6 inhibitors and metastatic breast cancer treatment (see the CDK4/6 inhibitors for metastatic breast cancer summary research table).

Learn about the strengths and weaknesses of different types of studies.

Study selection criteria: Randomized clinical trials with at least 1,000 participants with hormone receptor-positive, HER2-negative early breast cancer.


Study Population
(number of participants)


Percent Surviving with No Breast Cancer Recurrence—
Hormone Therapy plus CDK4/6 Inhibitor

Percent Surviving with No Breast Cancer Recurrence-
Hormone Therapy Alone
(no CDK4/6 Inhibitor)

Absolute Improvement in Survival with No Breast Cancer Recurrence with the Addition of CDK4/6 Inhibitor to Treatment with Hormone Therapy

Randomized clinical trials – abemaciclib

monarchE [1]






Randomized clinical trials – palbociclib












NS = No statistically significant difference between the 2 treatment groups


  1. Rastogi P, O’Shaughnessy J, Martin M, et al. Adjuvant abemaciclib plus endocrine therapy for hormone receptor-positive, human epidermal growth factor receptor 2-negative, high-risk early breast cancer: results from a preplanned monarchE overall survival interim analysis, including 5-year efficacy outcomes. J Clin Oncol. 2024 Jan 9 [Online ahead of print].
  2. Gnant M, Dueck AC, Frantal S, et al. for the PALLAS groups and investigators. Adjuvant palbociclib for early breast cancer: the PALLAS trial results (ABCSG-42/AFT-05/BIG-14-03). J Clin Oncol. 40(3):282-293, 2022.
  3. Loibl S, Marmé F, Martin M, et al. Palbociclib for residual high-risk invasive HR-positive and HER2-negative early breast cancer-the Penelope-B trial. J Clin Oncol. 39(14):1518-1530, 2021.

Updated 01/12/24