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The aim of this study is to study the two cases of acute lymphoblastic leukemia (ALL) who relapsed as acute myeloid leukemia (AML). Presented here are reports of two cases of pediatric ALL who developed change of lineage to AML at relapse. This change in phenotype, which involves the conversion of one phenotype to other phenotype during the course of disease or at relapse is a rare phenomenon rarely described in literature. The immunophenotypic and molecular findings are described. The present study emphasizes the need of immunophenotyping and molecular workup at relapse. Also adds to the repertoire of the published literature on this rare entity.

Acute promyelocytic leukemia (APL) has defined biology and clinical course that is, distinct from the other forms of acute myelogenous leukemia. It may present with potentially devastating coagulopathy and the sensitivity to retinoid differentiating agents, including all-trans retinoic acid and arsenic trioxide, hence a fast and definite diagnosis is imperative. Reciprocal 15, 17 translocation creates a PML/RARA fusion gene on the derivative chromosome 15, which can be detected by various molecular tests such as cytogenetics, fluroscence in-situ hybridization (FISH), reverse transcriptase-polymerase chain reaction. We present here a diagnostically challenging case, both morphologically and immunophenotypically proven to be APL, which was negative for the PML/RARA by FISH.