Q&A: Real-World Considerations of CDK4/6 Inhibitor Therapy in Breast Cancer

As treatment strategies for hormone receptor–positive (HR+) breast cancer continue to evolve, the role of the pharmacist has become increasingly integral in helping translate clinical trial data into real-world patient care. In this interview with Pharmacy Times, Julia Ziegengeist, PharmD, BCOP, a clinical pharmacist coordinator, breast medical oncology at Atrium Health Levine Cancer Institute, shared her perspective on how pharmacists navigate the complexities of CDK4/6 inhibitor therapy beyond what is outlined in clinical trials. From assessing comorbidities and prior treatment tolerance to managing drug interactions and financial barriers, Ziegengeist highlighted the nuanced, patient-centered considerations that shape therapeutic decision-making in everyday practice.

Ziegengeist also emphasized the pharmacist’s critical role within the multidisciplinary care team, particularly in coordinating monitoring, managing toxicities, and ensuring seamless communication between providers, nurses, and patients. Proactive follow-up and detailed care coordination to prevent gaps in treatment are crucial, especially when dose modifications or lab monitoring are required. Additionally, she addressed ongoing uncertainties in the field, including how to better define “high-risk” patients and apply emerging clinical trial data—such as findings from the monarchE (NCT03155997) and NATALEE (NCT03701334) trials—to broader patient populations.

Pharmacy Times: Beyond clinical trial eligibility criteria, what real-world patient factors—such as comorbidities, medication burden, or social determinants of health—most influence how pharmacists approach CDK4/6 inhibitor therapy in practice?

Julia Ziegengeist, PharmD, BCOP: Certainly, those comorbidities are going to play a huge role, and that’s not only what the patient’s currently experiencing, but also how they tolerated their prior treatment if they have received chemotherapy in the past. So, that’s going to enlighten us [regarding] how we expect patients may tolerate some of these CDK4/6 inhibitors and what we may need to potentially prevent for them. Also, drug interactions, because we know that ribociclib (Kisqali; Novartis Pharmaceuticals Corporation) is going to be more responsible for those than abemaciclib (Verzenio; Eli Lilly and Company)…. And then also just kind of thinking about the cost perspective. So if they need patient assistance, there may be one [drug] they qualify for over another.

Pharmacy Times: As a pharmacist coordinator, how do you work with multidisciplinary teams to streamline monitoring and follow-up for patients receiving CDK4/6 inhibitors, particularly when managing toxicity or dose modifications?

Ziegengeist: It definitely requires the full team, so everybody has to be on the same page about when the patient is starting, because we need to coordinate labs and sometimes EKG appointments. We have to know which day is cycle 1, day 1. Also, we have a hold for something like neutropenia, and you maybe want to hold for a week and then get labs again. That requires communication for the whole team to get them scheduled for something like that. Also, somebody needs to communicate…with the patient to tell them, “OK, your labs looked better, and you can restart,” so that that doesn’t fall through the cracks.

So I think we as pharmacists can follow up on those things. We can remind other members of the team about what needs to happen if it’s not clear. Because obviously…providers have a lot of patients. These nurses have a lot of patients that they’re following, and so making sure that those things happen [is] very key for us.

Pharmacy Times: Looking at the long-term data emerging from trials such as monarchE and NATALEE, what do you see as the most important remaining knowledge gaps for clinicians treating HR+ breast cancer?

Ziegengeist: I think we do need to have some of those nuances related to those lower- but still high-risk patients to try and help providers and patients feel more comfortable continuing with using those in those…lower- but still high-risk patients. Also, defining exactly what is high risk...we think that we have some idea. Clearly a grade 3, having positive lymph nodes, especially if you have a lot of positive lymph nodes, those are very clear-cut, straightforward risk factors. But there [are] probably some other things that we can take into consideration that can help us determine who really is a high-risk patient.