CHIP, ICUS, CCUS and other four-letter words

Clonal hematopoiesis can be identified by the presence of somatic mutations in blood or bone marrow even in individuals without a myeloid malignancy. Advances in DNA sequencing have led to the discovery that clonal hematopoiesis is remarkably common and occurs in a wide variety of settings, each often described by unique acronym. These distinctions can be useful as the implications of clonal hematopoiesis depend almost entirely on the clinical context in which it is identified. However, some generalizations can be made. The prevalence of clonal hematopoiesis increases with age, particularly after the fifth decade of life. Clonal hematopoiesis in normal individuals with very small clones is typically benign, while patients with clinically abnormal hematopoiesis, larger clones and more driver gene mutations appear to be at much greater risk. Understanding the significance of clonal hematopoiesis in the various contexts in which it occurs can influence how physicians assess risk, select therapies and counsel their patients. This concise review examines the implications of clonal hematopoiesis in several settings, including normal aging, aplastic anemia, unexplained cytopenias and patients receiving cytotoxic chemotherapy.