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An ASCO expert panel offered new guidance on cyclin-dependent kinase 4 and 6 (CDK4/6) adjuvant therapy for patients with early breast cancer.

As the panel noted in the rapid recommendation update published in the , the new guidance for abemaciclib (Verzenio) was based on a new of the monarchE trial that included 5-year efficacy outcomes. The experts also offered new recommendations for ribociclib (Kisqali) based on the recently published trial.

Panel co-chair Rachel Freedman, MD, founder and director of the Program for Older Adults with Breast Cancer at Dana-Farber Cancer Institute in Boston, explained the new evidence and recommendations in the following interview.

What are the recommendations for abemaciclib, and what are they based on?

Freedman: There aren't new recommendations for abemaciclib, just longer-term follow-up and changes in the FDA approval. Per the monarchE trial, abemaciclib for 2 years (in patients with node-positive breast cancer meeting the criteria for the study) added to the benefits of what was seen with endocrine therapy alone. Continued benefits and even a deepening of benefits over time were seen, so abemaciclib continues to be a recommended option for patients who would have met the criteria for the monarchE study.

What is the new recommendation for ribociclib, and what is that based on?

Freedman: This is based on the recently reported NATALEE trial, where patients with stage II and III breast cancer meeting the criteria for study entry received 3 years of ribociclib along with endocrine therapy versus endocrine therapy alone. This agent can now be considered as an option for patients.

Do you have any thoughts on which subgroups of patients might benefit most from CDK4/6 adjuvant therapy?

Freedman: We don't really know which subgroups may or may not benefit the most from these agents. Although we anticipate the patients at highest risk for recurrence may derive the most benefit in absolute terms, patients in all subgroups analyzed across these studies seem to benefit.

With every patient, there needs to be an individualized discussion that takes into account preferences, risk of side effects, risk of recurrence, and even cost as decisions are made on whether to use these medications. For some patients, taking these medications is "worth" the downsides. For others, it may not be the case.

What advice did the panel offer on the use of abemaciclib versus ribociclib in patients who meet the criteria for both monarchE and NATALEE?

Freedman: At this point, because of the longer-term data/follow-up available for abemaciclib, the 2- vs 3-year duration of therapy required (with abemaciclib vs ribociclib), and the presence of FDA approval, our panel favored initial consideration of this agent over ribociclib for patients who have met the criteria for either/both studies.

However, there may be cases where ribociclib is the preferred agent, such as in the case for side effect concerns or intolerability of treatment. With time, this may change, as more data become available and we continue to see the longer-term impacts on survival.

Is there anything else you want to make sure oncologists understand about these updates?

Freedman: Making individualized decisions with patients is key -- there is not a one-size-fits-all approach for use of these agents.

Read the study here and expert commentary about it here.