Tumor Immune Microenvironment Clusters in Localized Prostate Adenocarcinoma: Prognostic Impact of Macrophage Enriched/Plasma Cell Non-enriched Subtypes

Background: Prostate cancer (PCa) is characterized by significant heterogeneity in its molecular, genomic, and immunologic characteristics. Methods: Whole transcriptome RNAseq data from The Cancer Genome Atlas of prostate adenocarcinomas (n=496) was utilized. The immune microenvironment was characterized using the CIBERSORTX tool to identify immune cell type composition. Unsupervised hierarchical clustering was performed based on immune cell type content. Analyses of progression-free survival (PFS), distant metastases, and overall survival (OS) were performed using Kaplan-Meier estimates and Cox-regression multivariable analyses. Results: Four immune clusters were identified, largely defined by plasma cell, CD4+ Memory Resting T Cells (CD4 MR), M0 and M2 macrophage content (CD4 MRHighPlasma CellHighM0LowM2Low, CD4 MRLowPlasma CellHighM0LowM2Low, CD4 MRHighPlasma CellLowM0HighM2Low, and CD4 MRHighPlasma CellLowM0LowM2High). The two macrophage-enriched/plasma cell non-enriched clusters (3&4) demonstrated worse PFS (HR 2.24, 95% CI 1.46–3.45, p=0.0002) than the clusters 1&2. No metastatic events occurred in the non-macrophage-enriched clusters. Comparing clusters 3 vs 4, in patients treated by surgery alone, cluster 3 had zero progression events (p<0.0001). However, cluster 3 patients had worse outcomes after post-operative radiotherapy (p=0.018). Conclusion: Distinct tumor immune clusters with a macrophage-enriched phenotype and reduced plasma cell enrichment independently characterize an aggressive phenotype in localized prostate cancer that may differentially respond to treatment.