B-Lymphoblastic Leukemia Presenting with an Isoderivative Philadelphia Chromosome—A Rare Case Report and Review of Literature

Abstract The Philadelphia chromosome is seen in 5% of pediatric and 25 to 50% of adult cases of acute lymphoblastic leukemia (ALL). It is linked to aggressive illness with a dismal prognosis. Additional chromosomal abnormalities are not prevalent with translocation 9;22; nevertheless, isochromosome derivative [ider(22)] with this translocation is rarely recorded in the literature. This is the third instance of ider(22) in pediatric B-cell acute lymphoblastic leukemia (B-ALL). Bone marrow chromosome analysis by G-banding showed 46,XX,t(9;22)(q34;q11.2)[6]/46,XX,ider(22)(q10)t(9;22)(q34;q11.2)[14]. Fluorescence in situ hybridization (FISH) analysis for BCR::ABL1 fusion showed 40% of interphase cells with two and 35% with three fusion signals that were in concordance with the karyotype. The patient was categorized as National Cancer Institute (NCI) high-risk (HR) and started with HR chemotherapy according to Children's Oncology Group (COG) protocol. Postinduction remission assessment by flow cytometry showed 2.6% measurable residual disease. The case highlights significance of cytogenetic analysis despite availability of advanced techniques like FISH. The prognostic significance of concurrent ider22(q10) with t(9;22) is yet to be explored.