Abstract 2702: Prostate stromal transcriptome as biomarker of aggressive prostate cancer

Background: Prostate cancer has a heterogeneous prognosis. Discovery of molecular biomarkers that improve identification of potentially lethal prostate cancer could enhance the ability to determine which patients would benefit most from immediate treatment. Most prognostic biomarkers have focused on those in prostate tumors. However, it is increasingly recognized that the tumor microenvironment contributes to cancer aggressiveness and progression. We therefore examined whole transcriptome expression of the prostate stroma and associations with clinically significant, high-grade prostate cancer. Methods: We performed RNA-sequencing (Illumina TruSeq RNA Exome library preparation) of macrodissected stromal samples (adjacent to and distant from tumor) from 363 radical prostatectomy specimens from Health Professionals Follow-up Study and Physicians' Health Study participants. We performed a differential expression analysis comparing the gene expression and pathways of stroma adjacent to and distant from tumor. We also performed a cluster analysis and computed a single sample gene set enrichment analysis (ssGSEA) score to assess the association of our previously reported 25 stromal signature genes (Tyekucheva et al. 2017) to determine the association with Gleason score. Results: Eighty-eight genes as well as eight Gene Ontology pathways and fourteen Canonical pathways were differentially expressed (FDR<0.05) between tumor adjacent to and distant from tumor. Pathways included cell-substrate adhesion, muscle development, and cardiomyopathy. 30% of men had high-grade (Gleason score 8-10) tumors. We observed higher expression of the individual signature genes in the cluster enriched for high Gleason score tumors, and a higher stromal signature ssGSEA score was associated with high Gleason score (p=0.04). Conclusions: Pathways differentially expressed between stroma adjacent to and distant from tumor suggest known differences in cell types by location or a potential field effect. We observed that the direction of the association of the stromal signature with Gleason score agreed with our previous report. We are currently analyzing the full expression dataset to identify additional stromal genes associated with Gleason score and lethal prostate cancer, and performing multi-plex immunohistochemistry to assess stromal cell-type heterogeneity in regions of tumor and normal prostate across tissue microarrays. Citation Format: Yinglu Zhou, Chaoran Ma, Giuseppe Nicoló Fanelli, Lavinia Stefanizzi, Elizaveta Gazeeva, Lorelei A. Mucci, Massimo Loda, Svitlana Tyekucheva, Kathryn L. Penney. Prostate stromal transcriptome as biomarker of aggressive prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2702.