Trisomy 5: A Rare Isolated Finding in Pediatric B-lymphoblastic Leukemia

Background and Objectives: In acute leukemia, all diagnostic criteria and treatment protocols are based on cytogenetic and molecular genetic findings. Despite recent advances in molecular biology, cytogenetic studies still play a pivotal role in the sub-classification of B-lymphoblastic leukemia (B-ALL). B-ALL is characterized by clonal cytogenetic abnormalities with numerical chromosomal aberrations being more common. An extra copy of chromosome 5 is common to see in cases with hyper diploidy. However, a gain of chromosome 5 as a sole anomaly is exceptionally rare in B-ALL. To date, trisomy 5 as a sole abnormality is reported in few cases only. We aimed to report the clinicopathologic profile of this rare finding to increase knowledge and highlight the disease course of these patients.

Methods: We report a case of a 14-year boy presented with fever, lethargy and episodes of nasal bleeding for two weeks. He was admitted to the pediatric oncology unit at Indus hospital and health network, Karachi. Flowcytometry performed on peripheral blood using 8-color flowcytometry. Conventional karyotyping was performed by GTG banding. FISH panel was comprised of dual color dual fusion probes for BCR::ABL1 and ETV6::RUNX1 whereas break apart probe for KMT2A (Metasystem, Germany). Digital image analysis for karyotyping and FISH was done on Leica Biosystems, Cytovision MB8.

Results: Flowcytometry results were consistent with B-ALL. Cytogenetic analysis on his bone marrow aspirate revealed trisomy 5 as a sole abnormality with no evidence of any other clonal cytogenetic abnormality. FISH studies for BCR::ABL1, ETV6::RUNX1 and KMT2A showed no evidence of gene rearrangements.

Conclusion: Trisomy 5 is a very rare cytogenetic aberration. Only few cases reported in children. Inferior outcome is reported in both children and adults. The increasing number of reported cases raises the possibility of a distinct cytogenetic entity. Its prognostic and therapeutic implications are yet to be explored.