Absolute eosinophil count as predictive biomarker of irAEs in patients with metastatic renal cell carcinoma (mRCC) treated with immune checkpoint inhibitors (ICIs).

Abstract

345 Background: Nivolumab and ipilimumab are associated with immune-related adverse events (irAEs) and, to date, few biomarkers predictive of ICIs toxicity are reported in mRCC. Methods: We conducted a single-center, observational, retrospective study at Clinical Oncology Unit, Careggi University Hospital, Florence, Italy. We evaluated 43 patients (pts) with mRCC treated with ICIs from April 2013 to May 2020. Absolute Eosinophil Counts (AEC, N°/μL) were registered at baseline and at time of occurrence of irAEs. This study aims to evaluate whether the AEC could be a predictive biomarker of irAEs in patients with mRCC treated with ICIs. Results: Median age was 65 years and males were 81.4%. 10 pts received Nivolumab+Ipilimumab, while 33 pts received Nivolumab single agent. 74.4% pts (32/43) developed at least 1 irAE, 11.6% with G3-G4 irAEs. The most frequent first irAE was endocrine event (40.6% pts; 37.5% with hypo-/hyper-thyroidism). The baseline mean AEC was 163.1/μL in our cohort, in particular 132.2/μL in pts who did not develop irAEs and 176.7/μL in pts who developed irAEs (p=0.134). Among the pts who developed irAEs, the mean AEC was lower in pts with G1-G2 (153.1/μL) than in those with G3-G4 (330/μL; p=0.0013) irAEs. At the time of onset of the first irAE, the mean AEC increased to 247/μL (Δ 140.1%). Analyzing the trend of AEC from baseline to time of occurrence of irAE for the 32 pts who had developed at least one irAE, 53.1% (17 pts) showed an increasing trend; among these pts, the most frequent irAEs were endocrine occurring in 4/17 pts (23.6%). An increasing trend was also observed in the majority of pts who developed G1-2 (14/27, 51.9%) and G3-4 (3/5, 60.0%) irAEs. Additional analyzes are ongoing to identify appropriate cut-offs of AEC to better stratify patients. Conclusions: There is little evidence in the literature about the potential role of absolute eosinophil counts as a predictive biomarker of irAEs in patients with solid tumors treated with ICIs, and most refer to patients with melanoma. In this study we observed that the baseline AEC values in patients that will develop irAEs are higher than in those without irAEs and, among the former, the values are lower for patients with toxicity G1-G2 vs G3-G4. We also found an increase of the mean AEC from baseline to the onset of the first irAE. Of the patients who experience toxicity, most have an upward trend in AEC at the onset of the first irAE. Compatibly with all the limitations of a retrospective analysis, our is the first experience exploring the role of the eosinophil count in the development of irAEs in mRCC patients treated with ICIs, and a prospective study is ongoing in our Unit to confirm the role of the eosinophil count in patients treated with ICIs.