Multiplex Reverse Transcription-Polymerase Chain Reaction as Diagnostic Molecular Screening of 4 Common Fusion Chimeric Genes in Taiwanese Children With Acute Lymphoblastic Leukemia

Background: The classification of B-lineage acute lymphoblastic leukemia (ALL) by specific chromosomal translocations has prognostic implications for risk-directed therapy. Reverse transcription-polymerase chain reaction (RT-PCR) assay is a useful tool for detecting fusion transcripts from common chromosomal translocations of ALL cells. Methods: Multiplex RT-PCR and nested-PCR assays were used to detect ALL-type BCR-ABL1 transcripts of the t(9; 22), TCF-PBX1 transcripts of t(1; 19), the MLL-AF4 transcripts of t(4; 11), and 2 variants of ETV6-RUNX1 of the cryptic t(12; 21) in 148 leukemic samples upon diagnosis. The patients received risk-directed protocols of the Taiwan Pediatric Oncology Group-ALL-2002 that consisted of multiple chemotherapeutic agents of different intensities. Event-free survival (EFS) and overall survival (OS) rates were analyzed for genetic abnormalities detected by multiplex PCR and conventional cytogenetic analysis by the Kaplan-Meier method, and compared with the Mantel-Haenszel test. The Cox proportional hazards model was implemented to identify independent prognostic factors for EFS and OS. Results: In this cohort of Taiwanese children, the relative frequencies of the 4 translocations of B-lineage ALL were 8% with ALL-type t(9; 22)/BCR-ABL1, 4% with (1; 19)/TCF-PBX1, 2% with t(4; 11)/MLL-AF4, and 17.6% with t(12; 21)/ETV6-RUNX1. Patients with t(12; 21)/ETV6-RUNX1 fusion, hyperdiploidy, and t(1; 19)/TCF-PBX1 fusion had the most favorable outcomes, whereas those with the t(9; 22)/BCR-ABL1 fusion or t(4; 11) and other MLL gene rearrangement had poor prognosis (P<0.001 for EFS and OS). BCR-ABL1, MLL gene rearrangement, and very high-risk group were independent prognostic factors after Cox regression analysis. Conclusions: The biological factors of leukemia cells are associated with treatment outcomes in childhood ALL. Multiplex RT-PCR assay is an efficient and sensitive diagnostic tool that may improve the ability to accurately and rapidly risk-stratify children with ALL.