Clonal Hematopoiesis: Role in Hematologic and Non-Hematologic Malignancies

FLT3 Mutated Acute Myeloid Leukemia after CD19 CAR-t Cells

Chimeric Antigen Receptor T-cells have improved the life expectancy of severely pretreated patients with aggressive hematological cancers; for this reason, therapy-related myeloid leukemias are becoming of great concern in this field, despite their clonal phylogenesis and mutational landscape have not been fully explored yet. This case discusses a 33-year-old man with refractory large B-cell lymphoma, treated with Chimeric Antigen Receptor T-cell (CAR-T) therapy as the 7th line of treatment. Despite a persistent partial response, the patient developed therapy-related acute myeloid leukemia (t-AML) six months post-CAR-T, revealing pre-existing clonal hematopoiesis. The myeloid malignancy exhibited an unusual hypocellular/dysplastic pattern, progressing to an established blast phase with cytopenia. Treatment with demethylating agents and BCL2 inhibitors proved ineffective, leading to t-AML with hyperleukocytosis and FLT3-ITD gain, resulting in the patient's death. This case underscores the impact of severe pretreatment and bone marrow impairment in CAR-T-associated t-AML, emphasizing their role over insertional mutagenesis. Furthermore, it highlights the retention of classic therapy-related leukemia characteristics, including the potential for acquiring FLT3 mutations and displaying dysplastic morphology in these secondary leukemias.