Reducing Breast Cancer Recurrence: Ribociclib's Potential Compared with Abemaciclib

Breast cancer has become the most common cancer worldwide, with more than 2 million new cases annually. Advanced treatment approaches and early diagnosis have reduced mortality in recent years, but recurrence or metastasis remains a major problem. One breast cancer drug, ribociclib (Valamor), is a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor. Combined with endocrine (hormone-suppression) therapy, it previously provided a significant survival benefit for women with metastatic (stage 4) hormone receptor-positive, HER2-negative (HR+/HER2-) breast cancer and has approval from both the FDA (US Food and Drug Administration) and Turkey's Ministry of Health for this use.

This article discusses the effects of ribociclib plus endocrine therapy in patients with early-stage HR+/HER2- breast cancer. It draws on interim NATALEE results presented in Chicago at the American Society of Clinical Oncology (ASCO) 2023 Annual Meeting.

Postoperative Adjuvant CDK4/6 Inhibitors in Breast Cancer

Ribociclib plus endocrine therapy had previously shown a survival advantage in women with HR+/HER2- metastatic breast cancer. In recent years, the combination has also shown benefits in early-stage HR+/HER2- breast tumors.

Researchers conducted NATALEE to evaluate the combination in patients with early breast cancer, comparing ribociclib plus endocrine therapy (an aromatase inhibitor) with endocrine therapy alone.

After a median follow-up of 27.7 months, the 3-year invasive disease-free survival (IDFS) rate was 90.4% with the combination and 87.1% with endocrine therapy alone. This 3.3% difference represents a 25% relative reduction in recurrence risk with the addition of ribociclib.

These results offer a new treatment option for many patients with stage 2 or 3 hormone receptor-positive, HER2-negative disease.

The findings are an important development for patients with early breast cancer at high risk of recurrence.

Commentary and Discussion

Combining ribociclib with endocrine therapy offers considerable hope for preventing breast cancer recurrence and improves outcomes in early breast cancer. However, this approach may require closer monitoring over three years of treatment.

Comparison with Abemaciclib

NATALEE and MonarchE are two important studies examining CDK4/6 inhibitors (ribociclib and abemaciclib) combined with endocrine therapy in hormone receptor-positive, HER2-negative, node-positive, high-risk early breast cancer. Both showed that these combinations reduce recurrence risk and improve disease-free survival rates.

Only one of these combinations, abemaciclib plus endocrine therapy, has FDA approval for this use, based on the MonarchE results.

In MonarchE, the 4-year IDFS rate was 85.8% with abemaciclib plus endocrine therapy and 79.4% with endocrine therapy alone. Combining the treatments therefore improved the chance of disease-free survival by 6.4%. This indicates a significant extension of patients' survival.

By comparison, NATALEE reported 3-year IDFS rates of 90.4% with ribociclib plus endocrine therapy and 87.1% with endocrine therapy alone, an improvement of 3.3%. However, follow-up in MonarchE was longer, averaging 42 months versus 27.7 months in NATALEE, which must be considered when comparing the results.

Adverse effects were more frequent among patients receiving CDK4/6 inhibitors in both studies. In MonarchE, the most common were neutropenia (19.6%), leukopenia (11.4%) and diarrhea (7.8%) in patients receiving abemaciclib plus endocrine therapy. NATALEE reported gastrointestinal effects and joint pain, but their exact frequencies were not specified.

Both studies therefore show that CDK4/6 inhibitors combined with endocrine therapy reduce recurrence risk and prolong disease-free survival in early-stage HR+/HER2- breast cancer. However, each combination has particular adverse effects that may influence treatment selection and monitoring. Further research and a better understanding of long-term effects are needed.