Clinical outcomes and toxicity in metastatic breast cancer patients treated with first or second-line cyclin-dependent kinase (CDK) 4/6 inhibitors and endocrine therapy in Egypt.

INTRODUCTION

cyclin-dependent kinase 4/6 inhibitors (CDK4/6is) are widely used to treat hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) metastatic breast cancer (MBC). This study aimed to assess the real-world efficacy and tolerability of CDK 4/6i in the Egyptian population.

METHODS

prospective observational study for HR+/HER2- MBC treated in the clinical oncology department of Ain Shams University Hospitals, Egypt, between July 2022 and September 2024.

RESULTS

sixty-two patients were included (mean age, 53.8 years; range, 29-85). Thirty-one (50%) received CDK4/6is as first-line therapy and 31 as second-line therapy. Median follow-up time was 14.2 months (range 12-24 months). Thirty patients (48.3%) started on Ribociclib, 9 (14.5%) on Abemaciclib, and 23 (37.1%) on Palbociclib, with 15 patients switched from Ribociclib and Abemaciclib to Palbociclib due to logistical causes. Median progression-free survival (PFS) was 14 months (6-27 months) and 11 months for first- and second-line therapy, respectively. Patients and treatment characteristics did not significantly impact PFS. Ribociclib and Palbociclib most frequently caused neutropenia (70.0% and 68.4%, respectively), while Abemaciclib caused diarrhea (55.6%). The rate of dose reductions was 24.6%. Age was significantly correlated with a higher incidence of hematological (p=0.03) and nephrological toxicity (p=0.02). Furthermore, medical comorbidities were associated with a significantly higher frequency of grade 3-4 hematological events (p=0.02).

CONCLUSION

our findings demonstrate that CDK4/6is are both effective and well-tolerated for HR+//HER2- MBC patients within a diverse patient population. Additionally, this prospective evaluation supports the efficacy of lower-dose levels of CDK4/6is, without negatively impacting PFS.