Association of Erythrocyte-Related Indices with Immune-Related Adverse Events and Survival of Lung Cancer Patients Receiving Immune Checkpoint Inhibitors

<b>Background</b>: Lung cancer has the highest lethality rate among malignancies worldwide. Immunotherapy is one of the common treatments for lung cancer patients. There are two main types of immunotherapies: one targets programmed cell death 1 (PD-1), and the other targets programmed cell death ligand 1 (PD-L1). These two belong to the class of immune checkpoint inhibitors (ICIs). However, immune-related adverse reactions (irAEs) were the main reasons affecting its clinical therapeutic effect. <b>Methods</b>: This retrospective cohort study analyzed red blood cell count (RBC), hematocrit (HCT), erythrocyte mean corpuscular volume (MCV) and immunotherapy outcomes in 920 lung cancer patients receiving immunotherapy from April 2019 to May 2023. <b>Results</b>: We found that high levels of RBC (>4.105 × 10⁹, <i>p</i> = 0.007, OR = 0.467, 95%CI: 0.268~0.812) and MCV (>86.35, <i>p</i> = 0.017, OR = 0.0.441, 95%CI: 0.224~0.865) were significantly related to the better response of ICIs immunotherapy in patients. Patients with high levels of HCT (>39.75%, <i>p</i> = 0.035, OR = 0.737, 95%CI: 0.555~0.979) may have a lower rate of irAEs occurrence. Meanwhile, patients with a low level of RBCs (≤4.635 × 10⁹, <i>p</i> < 0.001, OR = 1.636, 95%CI: 1.365~1.960) may have a longer period of PFS (progression-free survival), and patients with RBC (≤4.43 × 10⁹, <i>p</i> = 0.033, OR = 0.480, 95%CI: 0.244~0.941) may have a longer time of OS (overall survival). <b>Conclusions</b>: The findings indicate that the levels of RBC, MCV and HCT were significantly associated with the response and irAEs of ICIs in lung cancer patients. The levels of RBC might act as a possible biomarker for predicting the survival of lung cancer patients who are receiving ICI therapy.