Impact of baseline serum IL-8 on metastatic hormone-sensitive (mHSPC) prostate cancer outcomes in the phase III CHAARTED trial (E3805).

Abstract

171 Background: IL-8 (CXCL-8) is a cytokine produced by leukocytes and tumor cells, which promotes inflammation, angiogenesis, anti-apoptosis, and metastasis. Our published training set identified serum IL-8 levels drawn within 28 days of androgen deprivation therapy (ADT) initiation as prognostic for shorter overall survival (OS). We sought to validate this finding using samples from CHAARTED patients treated with ADT +/- docetaxel for mHSPC. Methods: We assayed serum samples drawn ≤28 days from ADT initiation from 233 patients using the same Mesoscale multiplex ELISA assay as the training set. Multivariable Cox proportional hazards models adjusted for ECOG performance status, disease volume, and prior local therapy (radiation/prostatectomy vs. none) with IL-8 as continuous and binary variables. The training median 9.3 pg/mL was the a priori binary cutpoint. Fixed-effects meta-analysis of the training and validation sets was performed. Results: Higher IL-8 levels were prognostic for shorter OS and time to CRPC for ADT alone and ADT + docetaxel (Table) and were independent of disease volume or docetaxel use. Meta-analysis of binary IL-8 levels >9.3pg/mL from patients treated with ADT alone (training + validation cohorts) was prognostic for poorer OS (HR 1.8, 95% CI: 1.2-2.7, p= 0.007) and shorter time to CRPC (HR: 1.4, 95%CI: 0.99-1.9, p=0.057). The validation cohort’s baseline median IL-8 level was similar at 10 pg/mL. Conclusions: Higher IL-8 is prognostic for shorter time to CRPC and OS independent of docetaxel use, disease volume and presentation with metachronous or de novo metastatic disease. These findings support targeting IL-8 as a strategy to improve mHSPC outcomes.[Table: see text]