Dr Mouabbi on the Use of Ribociclib vs Abemaciclib in HR+/HER2– Breast Cancer

Jason Abdou Mouabbi, MD, assistant professor, Department of Breast Medical Oncology, Department of General Oncology, Division of Cancer Medicine, The University of Texas MD Anderson Cancer Center, discusses considerations for the use of ribociclib (Kisqali) vs abemaciclib (Verzenio) in patients with hormone receptor (HR)–positive, HER2-negative breast cancer.

The phase 3 NATALEE trial (NCT03701334) evaluated adjuvant ribociclib in patients with HR-positive, HER2-negative early breast cancer. The phase 3 monarchE trial (NCT03155997) investigated adjuvant abemaciclib plus endocrine therapy in this patient population.

The definitions of high-risk HR-positive, HER2-negative metastatic breast cancer differed between the monarchE and NATALEE trials, Mouabbi says. monarchE only enrolled patients with lymph node–positive disease, whereas NATALEE included patients with either lymph node–positive or –negative disease. Therefore, based on these trial populations, a broader range of patients with HR-positive, HER2-negative breast cancer qualifies for ribociclib than abemaciclib, Mouabbi notes.

Although cross-trial comparisons are generally not advisable, informally comparing the findings from these 2 studies may provide useful insights in the absence of head-to-head comparisons between ribociclib and abemaciclib in this setting, Mouabbi cautions. monarchE included a higher proportion of patients with disease involvement in 4 or more lymph nodes than NATALEE. Consequently, some breast cancer experts may advise the use of abemaciclib for the highest-risk patients with extensive lymph node involvement and the use of ribociclib for those with lode-negative or lower-risk disease, Mouabbi explains. However, treatment decisions based solely on these criteria are not straightforward, Mouabbi emphasizes.

The administration schedules and adverse effect (AE) profiles also differ between these 2 agents, providing further evidence that specific patients may benefit more from 1 drug over the other, according to Mouabbi. Abemaciclib is taken twice daily continuously, whereas ribociclib is taken once daily for 3 weeks followed by a 1-week break every cycle. Additionally, the treatment durations differ for each regimen. In NATALEE, ribociclib was administered for 3 years, whereas in monarchE, abemaciclib was administered for 2 years.

Patient involvement in the treatment decision-making process is crucial, Mouabbi emphasizes. Some patients may prefer 1 drug to the other because of its administration schedule, AE profile, or treatment duration, Mouabbi says. Other patients may only qualify for 1 of these agents based on the enrollment criteria of the 2 studies, Mouabbi adds. Ultimately, detailed discussions with patients are crucial, as patients should have a significant say in their treatment plan, Mouabbi concludes.