Abstract 3899: Genetic insights into clonal evolution from normal prostate epithelium to cancer via HGPIN

Backgrounds: Prostate cancer (PC) is one of the most prevalent cancers in the developed world, where its incidence is still increasing. Most PCs are thought to arise from high-grade prostatic intraepithelial neoplasia (HGPIN), a well-recognized precursor lesion. However, the genetic landscape of HGPIN and its relationship with normal prostate epithelium (NPE) and PC remains to be fully explored. Methods: To address these issues, we collected prostate tissue samples from five patients who underwent radical prostatectomy. Prostate tissue sections (3 mm thick) were fixed with an alcohol-based solution and prepared for dual immunostaining using AMACR/p63, in addition to hematoxylin-eosin staining, and subjected to laser-capture microdissection (LMD). Then, PC (n = 35), HGPIN (n = 71), and normal epithelium (n =244) samples were dissected and subjected to whole-exome sequencing (WES). Variant pathogenicity was assessed based on COSMIC and ClinVar databases. Furthermore, to investigate the mutation acquisition rate in the prostate epithelium, single cell-derived prostatic organoids established from three patients were analyzed using WES. Somatic single nucleotide variants (SNVs), indels, and copy number variations (CNVs) were identified. Results: A total of 10,047 somatic SNVs and indels were detected. The mutation rate was estimated to be 0.28 mutations/year/exon. Shared mutations were observed between NPE and HGPIN as well as between HGPIN and PC in some cases, suggesting a common clonal origin. Pathogenic FOXA1 mutations were frequently identified in both HGPIN and PC. While pathogenic FOXA1 mutations were also observed in NPE, none of these mutations were shared with HGPIN or PC, indicating that they likely represent independent mutational events. In one case, spatially separated multifocal cancers exhibited distinct FOXA1 mutations, each of which was shared with the adjacent HGPIN. In other cases, mutations were also shared between PCa, HGPIN, and NPE samples, although no known driver mutations were detected therein. These observations suggest that these cancers were derived from their precancer lesions with apparently normal histology, which progressed through HGPIN and PC. Phylogenetic analysis of these samples revealed that HGPIN and PCa diverged recently from a common ancestor. Conclusions: We successfully characterized somatic mutations and CNVs in apparently normal prostate epithelium, which were shared between HGPIN and adjacent PC in some cases. These findings provide new insights into the early genetic events driving PC development. Further studies are needed to fully elucidate the clonal evolution from NPE to PC, which may offer novel targets for early detection and intervention. Citation Format: Kohsuke Hishiki, Nobuyuki Kakiuchi, Yuki Teramoto, Koichi Watanabe, Kosuke Ieiri, Hirona Maeda, Tomonori Hirano, Yuki Kita, Takashi Kobayashi, Seishi Ogawa. Genetic insights into clonal evolution from normal prostate epithelium to cancer via HGPIN [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3899.