The Gut Microbiota in Hematologic Malignancies: Mechanisms, Clinical Associations, and Translational Opportunities

: Hematologic malignancies arise and progress within a systemic ecosystem in which the gut microbiota is an increasingly recognized, partially modifiable component. Across acute leukemias, chronic lymphocytic leukemia, plasma cell disorders, lymphomas, and clonal myeloid neoplasms, human studies consistently report reduced microbial diversity, depletion of barrier-supportive, short-chain fatty acid-producing commensals, and enrichment of Gram-negative, pro-inflammatory, or hospital-adapted taxa. These alterations are associated with pre-leukemic clonal expansion, adverse genetic and immunological features, progression from precursor conditions, and inferior outcomes after chemotherapy, immunochemotherapy, chimeric antigen receptor T-cell therapy, and allogeneic hematopoietic stem cell transplantation. Mechanistic work in animal models and ex vivo systems demonstrates that microbiota-derived signals and metabolites-including Th17/IL-17-skewing consortia and the lipopolysaccharide intermediate ADP heptose sensed by the cytosolic receptor ALPK1-can actively modulate hematopoietic stem and progenitor cell fitness, inflammatory circuits, and malignant cell survival, supporting a causal role in disease biology. At the same time, major knowledge gaps remain because most human cohorts are small, single-center, and cross-sectional, frequently rely on 16S rRNA profiling, and are vulnerable to dietary, geographic, and treatment-related confounding. Within this context, three translational domains appear particularly promising: pharmaco-microbiomics, microbiome-informed risk stratification, and rational microbiota-targeted interventions, particularly diet-based strategies and antimicrobial stewardship. Here, we provide an integrated, disease-spanning synthesis of these data, emphasizing clonal hematopoiesis and myeloid neoplasms as emerging examples of microbiota-marrow crosstalk and outlining practical priorities for embedding microbiome science into future hematologic trials. Routine microbiome profiling or empiric microbiota-directed therapies cannot yet be recommended in everyday hematology practice, but integrating microbiome science into prospective therapeutic and transplant trials offers a realistic path to improved disease modeling, biomarker development, and rational adjunctive strategies to enhance outcomes for patients with hematologic malignancies.