Abstract 250P
Background
Early palbociclib-related neutropenia has been associated with prolonged PFS (progression-free survival). However, there is limited real-world information. The aim of the study was to determine whether early neutropenia in our cohort of patients is associated with disease response to palbociclib combined with fulvestrant or aromatase inhibitor.
Methods
Retrospective study including all patients who started treatment with palbociclib between December 2016 and January 2021. Demographic and clinical data were obtained from the electronic clinical records. Primary endpoints included both PFS and OS (overall survival). Early neutropenia was defined as the nadir absolute neutrophil count (ANC) during the first 2 cycles of treatment. PFS and OS were analyzed through Kaplan–Meier survival curves comparing neutropenia grades using log-rank test to check differences between survival curves. Multivariate Cox proportional hazard regression model was also used to predict OS.
Results
A total of 78 patients were included. Demographic and clinical characteristics are shown in the table. Table: 250P
| Total patients (n=78) | |
| Age in years, mean±SD | 62±12.7 |
| Female, N(%) | 77(98.7%) |
| Weight in kg, mean±SD | 67.2±14.8 |
| Baseline ECOG PS 0-1, N(%) | 71(91.0%) |
| Line of therapy, N(%) 1 2 ≥3 | 55(70.5%) 16(20.5%) 7(9.0%) |
| Concomitant drug, N(%) Fulvestrant Aromatase inhibitor | 29(37.2%) 49(62.8%) |
| Baseline ANC, mean±SD | 4.7±2.4 |
Thirty-six patients (46.2%) stopped the treatment and 31 (86.1%) discontinued due to progression. Thirty-four patients (43.6%) required ≥ 1 dose reduction. In the first two cycles, 69 patients (88.5%) experienced grade 1–4 neutropenia. Patients who experience grade 2-4 neutropenia in the first two cycles were associated with significantly prolonged median OS (log-rank p=0.020). However, there was no significantly association with prolonged median PFS (log-rank p=0.228). After adjusting for potential cofounders (baseline ACN, age and weight), grade 2-4 neutropenia remained significantly and independently associated with prolonged OS (HR 0.30, 95% CI 0.11–0.81, p=0.018).
Conclusions
Early treatment-related neutropenia was significantly associated with a prolonged OS, supporting the suggestion that neutropenia could be a pharmacodynamic marker for palbociclib dosing.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.