Molecular Heterogeneity in Acute Promyelocytic Leukemia - a Single Center Experience from India

Atypical breakpoints and variant APL cases involving alternative chromosomal aberrations are seen in a small subset of acute promyelocytic leukemia (APL) patients. Over 7 different partner genes for RARA have been described. Although rare, these variants prove to be a diagnostic challenge and require combination of advanced cytogenetic and molecular techniques for accurate characterization. Heterogeneity occurs not only at the molecular level but also at clinico-pathological level influencing treatment response and outcome. In this case series we describe the molecular heterogeneity of APL seen in a single tertiary referral centre with a focus on seven variant APL cases from a single tertiary cancer center in India over a period of two and a half years. We discuss five cases with PLZF-RARA fusion and two novel PML-RARA variants, including a Bcr3 variant involving fusion of PML exon4 and RARA exon3 with an additional 40 nucleotides originating from RARA intron2, another involving exon 6 of PML and exon 3 of RARA with addition of 126 nucleotides, which mapped to the central portion of RARA intron 2 To the best of our knowledge this is the first of kind case series from India