6 Real-world Adherence and Persistence With Palbociclib Treatment Among Insured Patients With HR+/HER2– Metastatic Breast Cancer in the United States

Background/Significance

Palbociclib (Ibrance), the first oral cyclin-dependent kinase inhibitor, is standard care for hormone receptor–positive (HR+), HER2- advanced or metastatic breast cancer (mBC). Palbociclib adherence and persistence are necessary to achieve optimal clinical outcomes in patients treated in
real-world settings.

Materials and Methods

This was a retrospective cohort study of insured adults in the Optum Research Database, an administrative health care claims database capturing about 20% of commercial and Medicare Advantage Part D enrollees in the United States. Adults diagnosed with mBC between February 2015 and December 2019 who initiated palbociclib in the first-line (1L) setting were selected for analysis. The index date was the first fill date of palbociclib before or anytime after the mBC diagnosis. Continuous enrollment 12 or more months pre- and 1 or more months post index was required. Palbociclib treatment was evaluated over the variable follow-up period. Medication possession ratio (MPR) was calculated as palbociclib days’ supply between the first and last fill divided by the total time treated. MPR of 80% or more was considered adherent. Palbociclib discontinuation was defined by the occurrence of a 60- or 90-day gap in days’ supply, adjusted for inpatient stays during which time medication was assumed to be supplied by the facility. Persistence was calculated as the time to palbociclib discontinuation using Kaplan-Meier methods over variable follow-up.

Results

One thousand sixty-six patients initiated 1L palbociclib, with 811 patients receiving palbociclib with aromatase inhibitors (P+AI) and 255 patients receiving palbociclib with fulvestrant (P+F). Mean follow-up time was 17 (P+AI) and 16 months (P+F). Mean age was 67 years for P+F and 66 years for P+AI. Overall, 79.9% of patients were adherent; mean MPR was 0.88 (median, 0.94) within each group. During the variable follow-up period, 41.3% of patients receiving P+AI and 45.9% receiving P+F discontinued palbociclib. Among those who discontinued, 23.9% and 21.4% discontinued within the first 3 months, respectively. Median time to discontinuation was 19.9 months (P+AI) and
15.2 months (P+F); 59.1% receiving P+F and 68.7% receiving P+AI remained on palbociclib at 12 months post index (90-day gap).

Conclusions

This analysis suggests most patients are well adherent with 1L palbociclib and persist on therapy. Further research is needed to understand reasons for early discontinuation in real-world practice.

Author Affiliations:

Nicole M. Engel-Nitz,¹ Samantha M. Kurosky,² Mary Grace Johnson,¹ Michael P. Johnson, Xianchen Liu

¹Optum, Inc

²Pfizer Inc