The prognostic impact of peripheral blood eosinophil counts in metastatic renal cell carcinoma patients treated with nivolumab.

Although immune checkpoint inhibitors (ICIs) have gained approval for metastatic renal cell carcinoma (mRCC), the response rate is still limited. Therefore, it is urgent to explore novel markers of responses to ICIs that can help assess clinical benefits. Recently, it has been noted that peripheral blood eosinophil counts are an independent factor correlated with clinical outcome of ICIs in some types of cancer. We investigated peripheral blood absolute eosinophil counts (AECs) at baseline and 4 weeks after the initiation of nivolumab for mRCC patients between February 2016 and May 2022. In addition, we examined clinicopathological features including irAEs and analyzed the correlation between AECs and clinical efficacy of nivolumab. The median progression-free survival (PFS) and overall survival (OS) for all patients were 5.7 and 25.5 months, respectively. The median AECs in patients with irAEs were significantly higher at baseline and 4 weeks after the treatment compared to those without irAEs (p < 0.001 and p = 0.001). With the cutoff value of AECs of 329 cells/µL at 4 weeks after the treatment for prediction of irAEs, high-AECs groups had significantly higher number of responders compared with that in low-AECs group (p < 0.001). Accordingly, the PFS and OS were significantly better in patients with high-AECs group than those in low-AECs group (p = 0.03 and p = 0.009). High-AECs at 4 weeks after the treatment serve as the prominent surrogate marker associated with the incidence of irAEs and better clinical outcome in mRCC patients receiving nivolumab.