Oglio, Franca

Breast cancer is the most common cancer in women, causing more than 600,000 deaths every year. The human microbiome is increasingly recognized as a key regulator of cancer initiation, progression, and therapeutic response. Postbiotics—defined as non-viable microbial cells and/or their structural components and metabolites that confer health benefits—are emerging as promising and safer alternatives to live probiotics in oncology. This review provides a comprehensive mechanistic overview of the potential role of postbiotics against cancer, with a specific focus on breast cancer. Preclinical evidence demonstrates that selected postbiotics exert dose- and time-dependent anticancer effects against multiple breast cancer subtypes by modulating key oncogenic pathways (such as PI3K/AKT and NF-κB) and inducing epigenetic regulation through histone deacetylase inhibition. Beyond direct effects on tumor cell proliferation and apoptosis, postbiotics influence the breast cancer microenvironment by reshaping cytokine networks, suppressing pro-metastatic inflammation, and enhancing antitumor immune responses through the activation of NK cells and T cells. We also provide emerging links between microbiome composition, estrobolome activity, and breast cancer subtype-specific biology. Despite these encouraging findings, the clinical translation of postbiotics in oncology remains limited. Currently, only one registered clinical trial investigates postbiotics in the oncology setting (melanoma), and no clinical trials have specifically evaluated postbiotics in breast cancer patients. This highlights a substantial translational gap between preclinical evidence and clinical application. Accordingly, well-designed, tumor-specific clinical trials are urgently needed to validate the safety, efficacy, and therapeutic potential of postbiotics as novel strategies in personalized breast cancer management.

Abstract Backgroud. Breast cancer (BC) is the most common and deadly cancer in women worldwide. Emerging evidence highlights the role of gut microbiota in modulating breast cancer risk, treatment response, and recurrence through various mechanisms, including the production of biologically active compounds and metabolites. These non-viable microbial products and metabolic byproducts from probiotic fermentation, known as postbiotics, exert beneficial effects on the host without the need for live microorganisms. Postbiotics derived from Lacticaseibacillus species represent a novel class of therapeutics with potential anti-cancer properties. In this study, we investigated the therapeutic effects of an innovative postbiotic product (iPB), developed through sequential fermentation of L.paracasei NPB01 and L.rhamnosus GG, in BC experimental models. Methods. The following cell lines were used to represent main BC subtypes: MCF7 cells (ER+/HER2), MDA-MB-231 (triple negative breast cancer), SKBR3 (HER2+). MCF-10A (normal breast epithelial cells), Caco-2 (enterocytes), and peripheral mononuclear blood cells (PBMC) were used as control. Cell viability was assessed by colony formation assay. Apoptosis was evaluated using Annexin V/7-AAD staining, HLA class I surface expression by flow cytometry, and cancer cells migration by wound healing assay. Results. iPB exposure resulted in >50% colony formation reduction in MCF7, >30% in MDA-MB-231 and >40% in SKBR3 cells starting from 0.5 mg/ml for 72 h (p<0.01). iPB increased early and late apoptotic cell rate in all BC cell lines starting from 0.5 mg/ml for 72 h. On the contrary, iPB exposure up to 5 mg/ml for 120 h did not affect cell viability in control cells (MCF-10A, Caco-2, PBMC). 1.20 to 1.30 fold increase in HLA class I expression was observed in all BC cell lines after the exposure with iPB starting from the dose of 0.5 mg/ml for 72 h. A less intense HLA class I expression increase was observed in control cells after the iPB exposure. Cell migration process and inflammatory cytokines response were inhibited by the iPB exposure in all BC cell models. Conclusions. iPB reduces cell viability and cell migration in all main BC phenotypes. These effects parallel with HLA class I surface expression increase in all BC cell phenotypes, potentially enhancing immunogenicity. These findings suggest that iPB may represent a promising novel agent in BC treatment and prevention. Citation Format: Roberto Berni Canani, Chiara Luongo, Laura Pisapia, Franca Oglio, Roberta Di Santillo, Alessia Gaeta, Chiara Scocco, Marco Michelini, Vittoria Mauriello, Alessia Cadavere, Camilla Messuri, Saranya Chumsri, Dawn Mussallem. Postbiotic based on sequential fermentation of L.paracasei NPB01 and L.rhamnosus GG exerts antitumor activities against breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 312.