Abstract 4927: Tumor tissue microbiome in the high-grade serous ovarian cancer: a pilot investigation within the African American Cancer Epidemiology Study

Abstract Background: High-grade serous ovarian cancer (HGSOC) is the most common histological subtype of ovarian cancer. Notably, Black and African American (AA) women face a ∼40% higher mortality risk from this disease compared to White women. Recent studies have suggested that intratumor microbes may play a key role in shaping the tumor microenvironment and influencing the prognosis of ovarian cancer. However, to date, no studies have investigated the tumor microbiome in Black/AA women diagnosed with HGSOC using formalin-fixed paraffin-embedded (FFPE) samples and a whole metagenome sequencing approach. Methods: We analyzed tumor FFPE samples from 20 HGSOC cases who self-identified as Black/AA and participated in the African American Cancer Epidemiology Study (AACES). Tumor DNA was extracted using a standardized protocol, and microbial profiling was performed using 2bRAD sequencing for microbiome (2bRAD-M), a high-precision, reduced-metagenome sequencing technique that enables species-level resolution. To assess tumor microbial differences by cancer stage and age at diagnosis, we compared tumor tissue microbial diversity, taxonomic composition, and functional pathways. Conventional statistical analyses (two-sample t-test and analysis of variance) were employed to evaluate significant differences across groups. Results: 2bRAD-M sequencing successfully detected tumor microbial DNA in all 20 participants of this pilot study. A total of 285 microbial species were identified, including 160 genera and 11 phyla, from results that passed quality control assessments. The mean alpha diversity, as measured by the Shannon index, was 2.41, and the Chao1 index was 15. Compared to women with localized (stage 1 and 2, n=8) HGSOC, those with stage 3 HGSOC (n=12) exhibited higher Shannon (mean 2.45 vs. 1.57, p=0.12) and Chao1 indices (mean 21 vs. 13, p < 0.001). Stage 3 tumors also showed a higher relative abundance of microbial species from the phyla Pseudomonadota, Bacteroidetes, and Bacillota, compared to localized stage tumors (p < 0.001). Pathway analysis identified secondary bile acid biosynthesis as the most significantly enriched pathway in stage 3 tumors, with over 1.5-fold higher abundance of this pathway (p < 0.0001) than stage 1 and 2 tumors. Age at diagnosis was also associated with microbiome composition; women diagnosed at a younger age (<50) had higher Shannon and Chao1 indices compared to older women. Additionally, women with younger age at diagnosis vs. ≥50) were more likely to have a lower relative abundance of Bacteroidetes and a higher abundance of the prolactin signaling pathway. Conclusion: Our pilot findings suggest that HGSOC tumor microbiome features measured among Black/AA women differ by stage and age at diagnosis, and thereby may influence the progression of HGSOC. Further studies with larger sample size are warranted as the next step. Citation Format: Tengteng Wang, Lauren C. Peres, Jeffrey R. Marks, Courtney E. Johnson, Elisa V. Bandera, Joellen M. Schildkrau. Tumor tissue microbiome in the high-grade serous ovarian cancer: a pilot investigation within the African American Cancer Epidemiology Study [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 4927.