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A Phase II Study of Abemaciclib for Patients with Retinoblastoma-Positive, Metastatic Triple-Negative Breast Cancer
Shom Goel1,2, Bojana Jovanović1,2,3, Xiangying Chu4
1Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.
Purpose:
Cyclin-dependent kinase 4/6 inhibitors can significantly extend survival when given in combination with endocrine therapy in patients with hormone receptor-positive metastatic breast cancer. However, their activity has been relatively underexplored in patients with metastatic triple-negative breast cancer (mTNBC).
Patients And Methods:
We conducted a single-arm phase II study of abemaciclib monotherapy in patients with Rb-positive mTNBC. Patients were treated with abemaciclib 200 mg orally twice daily until disease progression, unacceptable toxicity, or withdrawal of consent. The primary endpoint was the objective response rate; secondary endpoints included progression-free survival (PFS), overall survival (OS), clinical benefit rate, disease control rate, and safety and tolerability.
Results:
A total of 27 patients were enrolled before the trial was closed early because of slow accrual. Patients had received a median of two lines of systemic therapy in the metastatic setting prior to enrollment. After a median follow-up of 28.5 months, the objective response rate was 0%, the clinical benefit rate was 14.8%, and the disease control rate was 22.2%. The median PFS was 1.94 months (95% confidence interval, 1.84-11.47), and the median OS was 8.44 months (95% confidence interval, 4.57-15.57). Median PFS and OS did not differ significantly based on androgen receptor and PD-L1 status. Pretreatment gene expression profiling of tumor tissue provided some hypothesis-generating insights into biological features associated with clinical benefit in this study. The most common treatment-related adverse events of grade 2 or higher were diarrhea (40.7%), neutropenia (40.7%), anemia (29.6%), and nausea (29.6%).
Conclusions:
Abemaciclib monotherapy did not show clinical activity in patients with pretreated Rb-positive mTNBC.
Insights
Abemaciclib monotherapy showed no clinical activity in patients with metastatic triple-negative breast cancer (mTNBC). This phase II study found a 0% objective response rate and limited survival benefits in pretreated patients.
Area of Science:
- Oncology
- Medical research
- Clinical trials
Background:
- Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors improve survival in hormone receptor-positive metastatic breast cancer.
- Their efficacy in metastatic triple-negative breast cancer (mTNBC) remains largely unexplored.
Purpose of the Study:
- To evaluate the efficacy and safety of abemaciclib monotherapy in patients with Rb-positive mTNBC.
- To determine the objective response rate (ORR) and survival outcomes in this patient population.
Main Methods:
- A single-arm phase II study involving 27 patients with pretreated Rb-positive mTNBC.
- Patients received abemaciclib 200 mg orally twice daily until disease progression or unacceptable toxicity.
- Primary endpoint was ORR; secondary endpoints included progression-free survival (PFS) and overall survival (OS).
Main Results:
- The study closed early due to slow accrual. The ORR was 0%, with a clinical benefit rate of 14.8% and disease control rate of 22.2%.
- Median PFS was 1.94 months and median OS was 8.44 months.
- Common adverse events included diarrhea and neutropenia (40.7% each).
Conclusions:
- Abemaciclib monotherapy demonstrated no significant clinical activity in pretreated Rb-positive mTNBC patients.
- Further research is needed to identify potential roles for CDK4/6 inhibitors in mTNBC treatment strategies.
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