Bolton, Kelly

ABSTRACT Condition Overview Clonal hematopoiesis (CH) refers to the presence of somatic variants in hematopoietic stem and progenitor cells (HSPC) that result in expansion over time. Diagnosis CH of indeterminate potential (CHIP) is operationally defined as pathogenic variants in oncogenic driver genes occurring in HSPCs at variant allele frequencies ≥ 2%. Clinical Associations CH is associated with increased risk for progressive cytopenias (also called clonal cytopenia of undetermined significance), hematological (predominantly myeloid but also lymphoid) neoplasms, cytosis (including monocytosis), and nonhematological conditions such as atherosclerotic cardiovascular and cerebrovascular disease. CH is linked to numerous other diseases including venous thromboembolism, type 2 diabetes mellitus, chronic obstructive pulmonary disease, osteoporosis, and gout, with a potential protective impact in Alzheimer's disease (AD). Management Recommendations CH detection is becoming increasingly common due to the ubiquitous use of somatic and germline sequencing in clinical practice, particularly, in oncology. The clinical implications of CH are most relevant in therapy‐related myeloid neoplasms (t‐MN), with antecedent CH clones in genes such as TP53, PPM1D, and/or CHEK2 having a clear selection advantage. Furthermore, genetic predisposition to CH has provided some clarity on the origin and evolution of CH. We are currently defining the role for CH assessment in individuals with persistent (≥ 4 months) unexplained cytopenias, in patients with malignancies prior to adjuvant cytotoxic chemotherapy and/or radiation or radionuclide therapy, screening prior to autologous hematopoietic stem cell transplantation or chimeric antigen receptor T cell (CAR‐T) therapy, and to work‐up potentially germline mosaic variants.