Abstract SY45-01: Characterizing the effects of the tumor microbiome on the response to immunotherapy

Abstract The presence of bacteria in solid human tumors has been documented for over 100 years. Still, it has only been in recent years that a more thorough characterization of this low biomass microbiome and its effects has been pursued. We have studied tumor biopsies that were taken before the initiation of treatment with checkpoint inhibitors (CPIs) and compared the tumor microbiome within these samples with the tumor immune landscape and the response to immune therapy. We found a few bacterial taxa and bacteria functions that were highly correlated with the response to CPIs. In my talk, I will present our main findings as well as our follow-up studies to validate the main results and dissect the mechanisms that underlie the effects of intra-tumor bacteria on the response to CPIs. Citation Format: Stephan Spahn, Yaara Zwang, Nancy Gavert, Michal Lotem, Mark Lythgoe, Ayelet Shai, Iris Barshack, Noam Shental, Simon Heidegger, Talia Golan, Jonathan Krell, Ravid Straussman. Characterizing the effects of the tumor microbiome on the response to immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr SY45-01.