HLH and TET2 Mutation Presenting after First Cycle of CLL Treatment.

Here we report development of hemophagocytic lymphohistiocytosis (HLH), along with unmasking of a TET2-mutated myeloid neoplasm, after initial doses of bendamustine and rituximab for longstanding chronic lymphocytic leukemia (CLL). After many years of CLL showing minimally progressive lymphocytosis, the patient's white blood cell count began to decline in parallel with neutrophil count, hemoglobin, and platelet count. Bone marrow biopsy showed partial CLL involvement; bendamustine+rituximab therapy was augmented with granulocyte colony-stimulating factor (g-CSF) and romiplostim to mitigate worsening pancytopenia, without response. Laboratory evaluation revealed a pattern supportive of the clinical impression of HLH, while bone marrow biopsy showed persistent CLL, new reticulin fibrosis, megakaryocytic proliferation, and 32% mutated TET2, but no compelling morphologic evidence of hemophagocytosis. The patient recovered with dexamethasone and g-CSF support.