Abstract PO1-03-10: Differential microbial metabolic pathways associated with resistance to neoadjuvant immunotherapy in locally advanced triple negative breast cancer

Abstract Differential microbial metabolic pathways associated with resistance to neoadjuvant immunotherapy in locally advanced triple negative breast cancer Background: It has previously been shown that microbial metabolic pathways are differentially activated in immunotherapy resistance, hence can serve as potential targets for therapeutic intervention. With the advent of Immune Checkpoint Blockers in the neoadjuvant setting of locally advanced (LA) TNBC, we hypothesized that similar microbial metabolite mediated resistance may be at play. We are presenting the real world data for neoadjuvant treatment in early TNBC along with a subset of tumor metabolite analysis. Method: 35 patients who received neoadjuvant pembrolizumab and chemotherapy for LA TNBC were identified at Moffitt Cancer Center between July 2019 to January 2023. These included 22 Caucasian, 5 African American, 2 Hispanic and 6 patients with undisclosed race. The age range was 33-78 years. The weight and Body Mass Index range was 55.3 kg-127.3 kg and 20.96-45.43 kg/m2 respectively. Nine patients had stage III disease while 24 had stage II breast cancer. The response was assessed in 33 patients; 20 patients (60.6%) achieved pathological complete response (pCR) and 13 (39.4%) had residual disease (RD). 1 patient developed severe immune mediated toxicity with colitis, hepatitis, myasthenia gravis leading to death while 1 patient had disease progression leading to drug discontinuation. Six patients developed immune mediated adverse events. We conducted untargeted metabolomic profiling on 24 patients to identify differentially abundant metabolites associated with pCR (ypT0/is ypN0) vs RD; 16 vs 8 patients respectively. Formalin fixed paraffin embedded (FFPE) slides from tumor tissue vs tumor bed were retrieved and histopathological evaluation of tumor cells was performed. 20 μm sections of FFPE block were used for untargeted metabolomics via liquid chromatography/mass spectrometry. Among the 200 metabolites detected, 63 were differentially abundant between pCR and tumor samples with RD. After correcting for false discovery rate, we observed striking differential activation of two microbial metabolic pathways. Samples with RD had significantly elevated kynurenine (OR-3.64 X1034, P-1.94 X 10-74 and kynurenine/Tryptophan ratio). The tryptophan, kynurenine pathway has been known to be overexpressed in patients resistant to immunotherapy and modulated by the microbiome. Similarly, the purine metabolic pathway, specifically microbiota-derived immunostimulatory metabolites- inosine, hypoxanthine, uric acid were significantly depleted in patients with RD (Inosine OR-0.54, p-0.007, Hypoxanthine OR-0.5, p-0.00039, uric acid OR: 0.41, P-0.003). Previously Inosine has been shown to increase the anti-tumor effects of immune checkpoint blockade by enhancing CD8+ effector T-cell function. Hence depletion of inosine, hypoxanthine and uric acid signals lack of an effector CD8 T cell response. Conclusion: Despite being a small study, it corroborates pCR rates noted in KEYNOTE 522 in the real world setting but shows significant concern for serious immune mediated adverse effects. This highlights the importance of stratifying patients who might be resistant to ICB or develop significant toxicities, thus deriving little to no benefit from standard neoadjuvant treatment. This underscores the need to develop precision-based treatment algorithms. The study represents one of the first investigations of differential abundance of microbial metabolites with immunotherapy resistance in LA TNBC. Our results highlight two microbially mediated mechanisms that could be targeted to improve pCR rates in LA TNBC. We are working to identify microbial metabolic pathways associated with immune mediated toxicity. Citation Format: Humaira Sarfraz, Brian Czerniecki, Zena Jameel, Michael Jaglal, Mostafa Eysha, Turkan Ozkul, Jameel Muzaffar, Aditi Saha, Sara Sarfraz, Fatima Zahra, Min Liu, Khushali Jhaveri, Melissa Sur, Adrianna Bagos-Estevez, Shahla Bari. Differential microbial metabolic pathways associated with resistance to neoadjuvant immunotherapy in locally advanced triple negative breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-03-10.