Brachial plexus chloroma as a presenting feature of relapse in a child with KMT2A-rearranged acute lymphoblastic leukemia, a case report

Approximately 30–40% of relapses in pediatric acute lymphoblastic leukemia (ALL) are extra-medullary. KMT2A gene rearrangements are common in patients with infantile ALL. Chloromas are rare tumors composed of collections of acute leukemic cells that typically involve the bone or skin. Exceptionally uncommon, chloromas invade the peripheral nervous system, a phenomenon termed “neuroleukemiosis.” We describe A 6-year-old girl with a history of pre-B ALL with CNS involvement and KMT2A rearrangement diagnosed initially at 4 months of age. During continuation therapy she developed a scalp mass that was confirmed to be a leukemic relapse. She underwent re-induction chemotherapy followed by blinatumomab with subsequent remission and proceeded to allogeneic hematopoietic cell transplant (HCT). Three years following HCT, she presented with brachial plexus palsy and was found to have a lymphoblastic chloroma invading the brachial plexus. Review of existing literature shows relapse in pediatric ALL patients presenting as brachial plexus chloroma has only been documented once before. It has long been suggested that KMT2A gene rearrangements play a role in development of chloromas in patients with AML, however it is still unclear what role KMT2A has in ALL. Here we report a rare case of ALL relapse that presented as a left arm palsy secondary to a leukemic chloroma invading the brachial plexus and aim to explore the potential role of KMT2A in the formation of ALL chloromas.