• Bin Wu, Rachel Jug, Catherine Luedke, Pu Su, Catherine Rehder, Chad McCall, Anand S Lagoo, and Endi Wang.
• Division of Hematology, Department of Medicine, Shengjing Hospital affiliated with China Medical University, Shenyang, People's Republic of China.
• Am. J. Clin. Pathol. 2017 Aug 1; 148 (2): 136-147.

ObjectivesLineage switch occurs in rare leukemias, and the mechanism is unclear. We report two cases of B-lymphoblastic leukemia (B-ALL) relapsed as acute myeloid leukemia (AML).MethodsRetrospective review of clinical and laboratory data.ResultsComplex cytogenetic abnormalities were detected in B-ALL for both cases with subclone heterogeneity. Postchemotherapy marrow biopsies showed trilineage hematopoiesis without detectable B-ALL. Cytogenetics in both showed stemline abnormalities. The cases were considered "occult" myelodysplastic syndrome (MDS) preceding B-ALL. The patients relapsed 6.5 and 9 months following induction, respectively. Case 1 relapsed as AML-M5 initially, was treated as such, and then relapsed again as B-ALL. Case 2 relapsed as AML-M6. Cytogenetics demonstrated persistent abnormalities. Both patients died soon after relapse.ConclusionsLineage switch between B-ALL and AML could be intermediated by occult MDS. A pluripotent progenitor likely undergoes neoplastic transformation, resulting in a genomically unstable clone. This leads to a repertoire of heterogeneous subclones that may be selected by chemotherapy. Lineage switch heralds a dismal clinical outcome.© American Society for Clinical Pathology, 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com

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