Clinical Implications of Clonal Hematopoiesis

Clonal hematopoiesis (CH)-an expansion of blood cells derived from a single hematopoietic stem cell-is a defining feature of hematologic cancers, but recently CH was also found to be a frequent consequence of aging. When aging-associated CH results from acquisition of a somatic mutation in a driver gene associated with leukemia, and this mutation is present at a variant allele frequency of at least 0.02 (2%) yet the patient does not meet World Health Organization diagnostic criteria for a hematologic neoplasm, this state is termed clonal hematopoiesis of indeterminate potential (CHIP). CHIP is present in approximately 10% to 15% of people older than 70 years and more than 30% by age 85 years and represents a precursor state for neoplasia akin to monoclonal gammopathy of undetermined significance. Recently, CHIP was unexpectedly found to be an important risk factor for cardiovascular events, with accumulating evidence supporting a mechanism of accelerated atherogenesis as a result of vascular inflammation driven by clonally derived monocytes/macrophages. Risk factors for CHIP include aging, male sex, cigarette smoking, and a common germline variant in the telomere-associated gene TERT. Clonal hematopoiesis can also occur after cytotoxic chemotherapy or radiotherapy for a solid tumor, after hematopoietic stem cell transplant, in the context of aplastic anemia, or after induction chemotherapy for acute leukemia; in each setting, CH has distinct clinical implications. This review summarizes recent studies of CH and CHIP and outlines challenges in clinical management of affected patients.