Abstract 6534: Bacterial infection as a modulator of tumor growth in ovarian cancer

Abstract Ovarian cancer exhibits the lowest survival rate among gynecologic malignancies, emphasizing the critical need for more effective treatment strategies and a comprehensive understanding of its progression mechanisms. Recent studies have suggested that certain microorganisms may contribute to the development and progression of various cancers. Our previous research identified specific microbiota in the uterus and ovaries, which were considered to be sterile. This finding raises the possibility that microbiota within the female reproductive organs may influence the progression of gynecologic cancers. In this study, we investigated whether bacterial communities contribute to the proliferation of ovarian cancer. To confirm the presence of bacteria in ovarian cancer tissues, we performed DNA fluorescence in situ hybridization (DNA FISH) using 16S rRNA probes specific to bacteria on ovarian cancer specimens. Approximately 60% of the tissue samples were found to harbor specific bacteria, predominantly located in the stroma. To evaluate the impact of these bacteria on tumor growth, we developed an in vivo mouse model by introducing bacteria found in ovarian cancer tissues via intraperitoneal injection, followed by intraperitoneal transplantation of mouse ovarian cancer cells. Tumor growth was significantly enhanced in the bacteria-exposed group compared to the control group, indicating that bacterial infection promotes tumor progression. Bacterial infection in the stromal area may induce chronic inflammation conducive to tumor growth, modulate the immune microenvironment, reprogram fibroblasts, and promote angiogenesis. We aim to further discuss these multifaceted roles and their implications in tumor biology and potential therapeutic strategies. Citation Format: Shinya Nakano, Ryosuke Sonobe, Miho Suzuki, Keiko Shinjo, Yutaka Kondo. Bacterial infection as a modulator of tumor growth in ovarian cancer [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 6534.