On-treatment derived neutrophil-to-lymphocyte ratio and response to palbociclib and letrozole: Analysis of a multicenter retrospective cohort and the PALOMA-2 study.

Abstract

1066Background: Relevant predictive biomarkers for cyclin dependent kinase 4 and 6 (CDK4/6) inhibitors have not been identified in hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC). We investigated whether dynamic changes in the peripheral immune cells can predict therapeutic response to CDK4/6 inhibitors in ABC with translational relevance. Methods: Postmenopausal women who received palbociclib and letrozole for HR-positive, HER2-negative ABC from tertiary referral centers were analyzed (n = 221; exploratory cohort). Pre- and on-treatment leucocyte, neutrophil, lymphocytes counts, neutrophil-to-lymphocyte ratio (NLR), and derived NLR (dNLR; neutrophil/[leucocyte-neutrophil]) were correlated with survival outcomes. Patients from the PALOMA-2 study (NCT01740427) treated with letrozole with or without palbociclib (n = 410 and 209, respectively) were analyzed for validation (validation cohort). Prospectively enrolled patients were subjected to immunophenotyping with flow cytometry to explore the immune cell dynamics after CDK4/6 inhibitor treatment. Results: In the exploratory cohort, palbociclib administration significantly reduced leucocyte, neutrophil, and lymphocyte counts on cycle 2 day 1. Not baseline, but on-treatment neutrophil and lymphocyte counts were associated with superior and inferior outcomes, providing predictive significance to on-treatment NLR and dNLR for progression-free survival (PFS; HR = 1.64 and 2.52; all P< 0.001). In the validation cohort, higher on-treatment dNLR was associated with inferior PFS in patients treated with palbociclib and letrozole (HR = 1.50 and P= 0.009 with 1.04 cut-off), whereas not correlated with outcome in placebo and letrozole-administered patients. Exploratory analysis revealed that CDK4/6 inhibitor prevented T cell exhaustion and diminished relative frequencies of myeloid-derived suppressor cells, both of which trigger antitumor immunity. Conclusions: On-treatment dNLR significantly predicted treatment outcome in HR-positive, HER2-negative ABC treated with palbociclib and letrozole, allowing early prediction of treatment response with mechanistic insights. Clinical trial information: NCT01740427 .