Study Finds High Adherence Rates, Low Adverse Effects Among Breast Cancer Patients Taking CDK 4/6 Inhibitors


Although the average wholesale price of the agents is more than $13,000, the investigators found that 9% of patients had a 0% co-pay throughout the 6-month period.

A retrospective study of patients with metastatic breast cancer found that those receiving cyclin-dependent kinase (CDK) 4/6 inhibitors had high rates of adherence, relatively few adverse effects (AEs), and low rates of patients stopping their medication.

According to researchers at AllianceRx Walgreens Prime and the Duquesne University School of Pharmacy, breast cancer is the second most commonly diagnosed cancer in women, totaling approximately 30% of all newly diagnosed cancers among women in the United States. Furthermore, up to 60% of those diagnoses are hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative.

CDK 4/6 inhibitors, such as palbociclib, abemaciclib, and ribociclib, are frequently used in combination with aromatase inhibitors as a first-line therapy regimen in patients with HR-positive, HER2-negative advanced or metastatic breast cancer. The therapy functions by lowering estrogen levels to prevent the spread of the disease.

Although the regimen is effective, the authors noted that if disease progression continues, there are limited data regarding the efficacy of switching to another CDK 4/6-containing regimen.

In the study, the authors analyzed the records of 2906 patients receiving either palbociclib, abemaciclib, and ribociclib between January and October 2019. The patients were divided into several groups, including those receiving CDK 4/6 inhibitor monotherapy (400 patients), those receiving a CDK 4/6 inhibitor with another oncolytic agent (67 patients), and those receiving a CDK 4/6 inhibitor with both an oncolytic and a hormone therapy (341 patients). Nearly all of the patients (2098) were on a prescribed combination therapy with a CDK 4/6 inhibitor and a hormonal therapy agent.

The investigators also reviewed prescription fill history in order to determine whether patients were on the appropriate dual therapy and were adherent to their medications.

During the 6-month investigational period, patient adherence to oncolytic agents was higher than the average adherence rates reported in prior studies, according to a press release. Furthermore, lead author of the study Lakyn Husinka, PharmD, said more than 60% of the patients reported no AEs during the time period, and less than 5% discontinued their therapy.

Notably, although the average wholesale price of the agents is more than $13,000, the investigators found that 9% of patients had a 0% co-pay throughout the 6-month period.

According to Huskina, the adverse drug event (ADE) results and the average co-pays can influence prescribers’ decisions when initiating therapy.

“Since ADEs and high co-pay costs are barriers for patients to start or continue medications, having a better understanding of these attributes can help tailor agent choice to the patient,” she said in the statement. “Additionally, having a better understanding of ADEs and adherence barriers experienced by patients prescribed 1 of the study medications will aid clinicians during patient interactions to help address and decrease these patient challenges.”


AllianceRx Walgreens Prime studies the use of cyclin-dependent kinase 4/6 inhibitors in breast cancer patients [news release]. AllianceRx Walgreens Prime; May 11, 2020. Accessed May 13, 2020.

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