Acute leukemia with PICALM–MLLT10 fusion gene: diagnostic and treatment struggle

Patients with various hematologic malignancies, including acute lymphoblastic leukemia (ALL), acute myeloblastic leukemia (AML), diffuse histiocytic lymphoma, and granulocytic sarcoma, have sometimes been shown to carry the PICALM–MLLT10 fusion gene (alias CALM–AF10) by various cytogenetic methodologies. Cases with the PICALM–MLLT10 fusion gene can involve a diagnostic dilemma for the following reasons: (1) the fusion gene occurs very rarely, (2) the cases do not have a distinct myeloid or lymphoid morphology and cells often appear immature, (3) cases usually have a mixed T-cell and myeloid phenotype, and (4) cases often have a mixed clinical presentation (e.g., mediastinal mass in a patient with AML). A 27-year-old woman was diagnosed with AML with the PICALM–MLLT10 fusion gene. The patient was treated on an AML regimen and achieved a complete remission. Although the reported treatment of these patients varies greatly, outcome remains very poor in the vast majority. Furthermore, central nervous system involvement at diagnosis and relapse are reported in pediatric populations. Routine acute leukemia fluorescence in situ hybridization panels do not include a probe for the PICALM–MLLT10 fusion gene, and therefore diagnosis can be made only when karyotyping is available; that delay can result in initial misdiagnosis and mistreatment. The case report and literature review here (including discussion of the poor prognosis and of management, including CNS prophylaxis) are intended to raise awareness and to inform about PICALM–MLLT10 in acute leukemia.