Impact of adding palbociclib on treatment adherence to ongoing adjuvant endocrine treatment in the global randomized PALLAS randomized trial in patients with early breast cancer.

Using patient-reported outcomes (PROs) and more objective measures, we evaluated adherence to adjuvant palbociclib and ET in the PALLAS trial, and the impact of palbociclib on ET adherence.The open-label, global, phase 3 PALLAS trial randomized patients with hormone receptor-positive (HR+), HER2-negative stage II-III breast cancer (1:1) to either 26 cycles of palbociclib (125 mg/day for 21 days and then 7 days off) plus adjuvant ET, versus ET alone. After 23.7 months median follow-up, palbociclib was stopped due to futility of the intervention and patients were moved to follow-up. For each cycle, daily adherence to ET was measured with study diaries; for palbociclib, study diaries and pill counts. At cycles 2, 3, 6, 12, 18 and 24, patients completed the Morisky Medication Adherence Scale-4 plus an additional item and the McHorney Adherence Questionnaire. Mean persistence was defined in months from treatment initiation to cessation.Four thousand six hundred eighty-eight of 5796 total PALLAS participants were included. Across all cycles, mean daily ET adherence values measured by study diary were > 98.0% and did not differ between treatment arms. Mean persistence to ET was similar between arms (19.2 months for palbociclib + ET vs. 19.6 months for ET alone). However, patient-reported maximal ET adherence was higher across time for palbociclib + ET compared to ET alone (p ≤ 0.0001, modified MMAS-4; p = 0.05, McHorney).In the PALLAS trial, addition of palbociclib did not decrease adherence to adjuvant ET. Though numbers declined over time, daily adherence for palbociclib and ET remained relatively high at each cycle.The trial is registered with ClinicalTrials.gov (NCT02513394; 07-31-2015) and EudraCT (2014-005181-30).