Langerhans Cell Histiocytosis Associated With Chronic Myeloid Leukemia: A Pediatric Case Report

Langerhans cell histiocytosis (LCH) is a rare clonal neoplasm driven by activating mutations in the MAPK pathway, leading to accumulation of pathological Langerhans cells in various tissues. LCH is increasingly associated with secondary malignancies, including leukemias, lymphomas, and solid tumors. However, chronic myeloid leukemia (CML) has not previously been reported in association with LCH. Here, we describe a rare case of CML arising in the setting of active LCH in a pediatric patient.

A 15-year-old boy was initially diagnosed at age 11 with single-system multifocal skeletal LCH. He received 12 months of vinblastine and prednisolone per the LCH-III protocol but failed to achieve remission and was lost to follow-up. Two years later, he re-presented with fever, bone pain, leukocytosis, anemia, and thrombocytosis. Bone marrow analysis was consistent with CML and PCR confirmed BCR::ABL1 p210-positive CML. PET and MRI demonstrated concurrent active LCH lesions. The patient was treated with imatinib and cladribine, achieving complete hematologic and molecular remission of both diseases within 7 months.

This rare association of CML with LCH expands the recognized spectrum of LCH-associated malignancies. It underscores the importance of long-term surveillance in LCH patients, with particular vigilance for secondary malignancies. It also highlights the need for further research into possible biological relationships between histiocytic and myeloid neoplasms.