The lung immune prognostic index (LIPI) was first reported to predict the effectiveness of immune checkpoint inhibitors in patients with metastatic non-small cell lung cancer and there are no studies investigating the predictive value of LIPI for patients with PCa. This study explores the prognostic value of the LIPI in patients with metastatic hormone-sensitive prostate cancer (mHSPC) and metastatic castration-resistant prostate cancer (mCRPC).Data from 502 patients with mHSPC primarily treated with maximal androgen blockade (MAB; 89% of patients received MAB) and 158 patients with mCRPC who received abiraterone were retrospectively analyzed. All cases were classified into LIPI-good, LIPI-intermediate, and LIPI-poor groups based on their LIPI score as calculated with the derived neutrophil-to-lymphocyte ratio and lactate dehydrogenase level. The potential for LIPI to be used in predicting mCRPC-free survival (CFS), prostate-specific antigen (PSA) response, PSA-progression-free survival (PSA-PFS), and overall survival (OS) was analyzed. A propensity score matching (PSM) methodology was performed to balance the baseline factors of the different groups.In the mHSPC cohort, patients of the LIPI-good (mCFS: 25.7 months; mOS: 93.3 months), LIPI-intermediate (mCFS: 14.8 months; mOS: 51.9 months), and LIPI-poor group (mCFS: 6.8 months; mOS: 18.5 months) had sequentially worse clinical outcomes (P<0.001 for all pairwise comparisons). The results remained consistent after PSM. Multivariate Cox regression further confirmed that LIPI was an independent predictor of survival outcomes. Subgroup analysis verified that LIPI was associated with an unfavorable prognosis in all subgroups except for cases with visceral metastases or those receiving abiraterone or docetaxel. As for patients with mCRPC receiving abiraterone, LIPI was also an indicator of poor prognosis. Specifically, cases in the LIPI-good, LIPI-intermediate, and LIPI-poor groups had a ladder-shaped worse PSA response [71.4% (50/70) vs. 56.5% (39/69) vs. 36.8% (7/19); P=0.015], PSA-PFS (14.9 vs. 9.3 vs. 3.1 months; P<0.001), and OS (14.6 vs. 32.3 vs. 53.4 months; P<0.001). The results were robust even after PSM. Multivariate Cox regression confirmed that LIPI was an independent prognosticator of PSA-PFS and OS in patients with mCRPC treated with abiraterone.This study demonstrated that the baseline LIPI was a significant prognostic biomarker for patients with both mHSPC and mCRPC and could potentially facilitate risk classification and clinical decision-making.2023 Annals of Translational Medicine. All rights reserved.