Recent studies have revealed that clonal hematopoiesis of indeterminate potential (CHIP) is an important risk factor for therapy-related myeloid neoplasms (t-MNs). CHIP is currently defined as a clonal hematopoietic population carrying somatic point mutations in 1 of the leukemia-associated genes. Patients with t-MNs often present with chromosomal abnormalities in addition to somatic point mutations. It remains unclear whether chromosomal abnormalities can cooccur with point mutations as part of CHIP. Here we report that 3 of 14 patients with t-MNs had low amplitude but detectable chromosome arm-level copy number alterations (CNAs) in the peripheral blood samples that were taken at the time of their primary cancer diagnosis and before exposure to therapy. These CNAs were the same CNAs seen in t-MN bone marrow samples and affected the same allele, suggesting the same clonal origin. These data suggest that not only somatic point mutations but also chromosome arm-level CNAs are detectable as CHIP and preexist before patients' exposure to chemotherapy and/or radiation therapy. These data suggest that screening of both somatic point mutations and CNAs might allow more complete ascertainment of CHIP.