Microbiome Modulation for the Treatment of Solid Neoplasms

The interplay between the human gut microbiome and the immune system has sparked growing interest in microbiome modulation as a therapeutic strategy in oncology. Preclinical studies have identified specific bacterial species linked to improved responses to immune checkpoint inhibitors (ICIs), leading to clinical investigations in melanoma, renal cell carcinoma (RCC), and non-small cell lung cancer (NSCLC). The stool bacterial abundance of Ruminococcaceae, Akkermansia, and Bifidobacterium correlates with favorable clinical outcomes, whereas the disruption of the gut microbiome through antibiotics before or during ICI initiation is associated with higher rates of primary resistance and shorter survival. Biomarkers such as TOPOSCORE have been developed to better predict ICI benefits and estimate dysbiosis and treatment responses. Several microbiome-modulating strategies have shown potential in patients receiving treatment with ICIs-for instance, high dietary fiber intake may be linked to improved outcomes. As a separate strategy, certain probiotics appear to enhance clinical activity in early trials when incorporated into ICI-based regimens. Finally, fecal microbiota transplantation has shown safety and efficacy in ICI-refractory melanoma and yielded encouraging results in treatment-naïve patients with melanoma, NSCLC, and RCC. Although several compelling signals have been observed to date with microbiome manipulation, the field is lacking large, definitive randomized trials-these are indeed a prerequisite for any of the highlighted strategies to become a standard of care.