Retrospective Analysis Provides Insight into Treatment-Emergent Neutropenia Among Patients with Metastatic Breast Cancer Treated with Ribociclib or Palbociclib

Real-world data showed that patients with metastatic breast cancer receiving palbociclib had a numerically higher rate of neutropenia than patients receiving ribociclib.

After the administration of CDK4/6 inhibitors ribociclib and palbociclib for hormone receptor–positive metastatic breast cancer, neutropenia is the most common adverse event.

In patients receiving these therapies, data are lacking to compare the incidences of treatment-emergent neutropenia. Lee Schwartzberg, MD, FACP, Medical Oncologist, Breast Cancer, West Cancer Center & Research Institute, Germantown, TN, and colleagues presented real-world data exploring the incidence, duration, and severity of treatment-emergent neutropenia, based on a retrospective analysis of administrative claims and electronic health records.

Two mutually exclusive cohorts of patients with metastatic breast cancer were treated with ribociclib or palbociclib. Patients were matched 1:1 based on year of treatment start and age. Previous baseline activity was required for ≥6 months.

To evaluate incidence rates of treatment-emergent neutropenia from January 1, 2015, to December 31, 2018, in patients receiving ribociclib or palbociclib, the MarketScan claims databases were used. From the Optum deidentified Electronic Health Record Dataset, data on neutropenia severity and duration were acquired. Neutrophil counts from lab tests (grade 1/2, 1000-1500/µL; grade 3, 500-1000/µL; grade 4< 500/µL) within the first 180 days of treatment were used to grade neutropenia severity. Kaplan-Meier analysis was used to estimate the duration of neutropenia, characterized as the period of time between first aberrant laboratory result and those showing resolution. One hundred fifty-two patients from the MarketScan database were included in the ribociclib and palbociclib groups after 1:1 matching, and 168 matched patients from the Optum database were also included.

In 38 (25%) patients in the palbociclib group and 25 (17%) patients in the ribociclib group, neutropenia was reported. The rate of neutropenia per person-treatment year was higher in the palbociclib group at 0.5 (95% confidence interval [CI], 0.4-0.7) when compared with the ribociclib group at 0.4 (95% CI, 0.3-0.6).

Although statistical significance was not demonstrated due most likely to small sample size, neutropenia rate ratio between treatments (palbociclib vs ribociclib) was 1.4 (95% CI, 0.8-2.3). Whereas the severity of neutropenia with palbociclib and ribociclib was similar at 32% for grade 1/2 and 4% for grade 4, it differed at grade 3, which was 35% for palbociclib and 26% for ribociclib. For grade 3 or 4 neutropenia (palbociclib vs ribociclib), the rate ratio was 1.3 (95% CI, 0.9-1.8). For palbociclib compared with ribociclib, the median neutropenia duration was significant, at 29 days compared with 20 days (P <.01).

Considering best possible practices for the management of neutropenia is an integral component of the treatment of hormone receptor–positive metastatic breast cancer. Clinicians may want to consider the impact of treatment and real-world data regarding rates of neutropenia, especially a higher rate of grade 3 neutropenia and a longer duration of neutropenia in patients receiving palbociclib therapy.

Source: Schwartzberg LS, Zarate JP, Chandiwana D, et al. Real-world incidence, duration, and severity of treatment-emergent (TE) neutropenia among patients (pts) with metastatic breast cancer (MBC) treated with ribociclib (RIB) or palbociclib (PAL). J Clin Oncol. 2020;38(15_suppl). Abstract e13048.