The silent pharmacist: Harnessing the gut microbiome to improve therapy in hematologic malignancies

The gut microbiome, a complex ecosystem of microorganisms, is now recognized as a key determinant of drug efficacy and toxicity, giving rise to the field of pharmacomicrobiomics. This review decodes the profound influence of the gut microbiome on treatment outcomes for hematologic malignancies. We explore the tripartite mechanistic pathways through which gut microbes act: the direct enzymatic biotransformation of chemotherapeutic agents, the indirect immunomodulation of systemic and anti-tumor responses, and the preservation of mucosal barrier integrity to prevent devastating complications like graft-versus-host disease (GVHD). The manuscript details how the microbiome interacts with specific drug classes, from conventional chemotherapies like cyclophosphamide to cutting-edge immunotherapies like immune checkpoint inhibitors and CAR-T cells, shaping their clinical success. Furthermore, we discuss the translational potential of targeting this "silent pharmacist" through fecal microbiota transplantation, next-generation probiotics, and dietary interventions. Finally, we highlight the main translational opportunities, current limitations, and future clinical priorities for integrating microbiome science into hematology, paving the way for more personalized and improved cancer care.