Effect of Dose Modifications of Ribociclib and Endocrine Therapy for Patients with Estrogen Receptor–Positive/HER2-Negative Metastatic Breast Cancer

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With the approval of cyclin-dependent kinase (CDK)4/6 inhibitors, treatment outcomes for patients with estrogen receptor (ER)-positive/HER2-negative metastatic breast cancer (MBC) have improved.

Approximately 35% to 57.5% of patients require a dose reduction during treatment with ribociclib, based on data from clinical trials.

Additional efficacy data are needed, focused on the potential impact of dose reduction. Therefore, using patients from 3 Danish oncology departments, researchers conducted a retrospective cohort study of patients with ER-positive/HER2-negative MBC.

From electronic health records, researchers compiled data on progression-free survival (PFS) and tolerability. In total, included in the analysis were data from patients (N = 128) who initiated ribociclib treatment for ER-positive/HER2-negative MBC between January 1, 2018, and March 31, 2020. Excluded from the study were patients who were previously treated with another CDK4/6 inhibitor, had concurrent malignancies (excluding T1 melanoma or nonmelanoma skin cancer), or had a Child Pugh score ≤B. The overall median PFS was 19.2 months. There was no decrease in median PFS in the cohort of patients with ≥1 dose reductions.

Apart from neutropenia, reported adverse events were generally mild (grade 1-2). With reports of grade 3 and 4 neutropenia occurring in 45.3% and 7% of patients, respectively, the frequency of adverse events was in alignment with previous reports. Neither previous treatment with chemotherapy, metastatic bone lesions, performance status, nor age, were considered risk factors for developing neutropenia. Between patients treated with a final dose of 400 mg or 200 mg, the PFS analysis of patients receiving ribociclib at a reduced dose did not differentiate.

Patients treated with fulvestrant compared with an aromatase inhibitor, and patients with baseline lymph node involvement had lower odds of a dose-reduction requirement.

The investigators’ findings suggest that there is no compromise in safety and efficacy of treatment associated with dose reduction of ribociclib. These findings further corroborate and support translation of MONALEESA trial results to real-world clinical practice.


Kristensen KB, Thomsen IMN, Berg T, et al. Dose modifications of ribociclib and endocrine therapy for treatment of ER+ HER2- metastatic breast cancer. Breast Cancer Res Treat. 2021;188:799-809.

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