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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.

The CDK4/6 inhibitors abemaciclib (Verzenio) and ribociclib (Kisqali) are FDA-approved for the treatment of some hormone receptor-positive early breast cancers.

Hormone therapy plus abemaciclib or ribociclib may reduce the risk of breast cancer recurrence (a return of breast cancer) better than hormone therapy alone in some people with hormone receptor-positive, HER2-negative early breast cancers at high risk of recurrence.

Learn more about abemaciclib and ribociclib (including side effects) and early breast cancer treatment.

Learn about CDK4/6 inhibitors and metastatic breast cancer treatment.

Learn about guidelines for the treatment of early breast cancer.

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

Study Population
(number of participants)

Follow-up
(years)

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]

5,637

5

84%

76%

8%

Randomized clinical trials – ribociclib

NATALEE [2]

5,101

4

89%

84%

5%

Randomized clinical trials – palbociclib

PALLAS [3]

5,761

4

84%

85%

NS

PENELOPE-B [4]

1,250

6½

82%

80%

NS

NS = No statistically significant difference between the 2 treatment groups

References

  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. 42(9):987-993, 2024.
  2. Fasching PA, Stroyakovskiy D, Yardley DA, et al. Ribociclib plus endocrine therapy in hormone receptor-positive/ERBB2-negative early breast cancer: 4-year outcomes from the NATALEE randomized clinical trial. JAMA Oncol. 2025 Sep 25 [Online ahead of print].
  3. 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.
  4. Loibl S, Martin M, Bonnefoi H, et al. Final survival results from the PENELOPE-B trial investigating palbociclib versus placebo for patients with high-risk HR+/HER2- breast cancer and residual disease after neoadjuvant chemotherapy. Ann Oncol. 36(7):832-837, 2025.

Updated 10/01/25