Lineage Switch Between B-Lymphoblastic Leukemia and Acute Myeloid Leukemia Intermediated by "Occult" Myelodysplastic Neoplasm: Two Cases of Adult Patients With Evidence of Genomic Instability and Clonal Selection by Chemotherapy.

OBJECTIVES

Lineage 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).

METHODS

Retrospective review of clinical and laboratory data.

RESULTS

Complex 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.

CONCLUSIONS

Lineage 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.