B-388 Clinical Performance of Xpert BCR-ABL Ultra Assay for Isoform p210 Quantitation

Abstract

Abstract Background Chronic myelogenous leukemia (CML) is one of the most common hematologic neoplasms. More than 95% of patients with CML have the distinctive Philadelphia chromosome (Ph1) that results from a translocation between the chromosomes 9 and 22, and consequently in the BCR::ABL1 fusion gene. This fusion gene produces a tyrosine kinase with deregulated activity that plays a key role in the development of CML. Monitoring BCR::ABL transcript levels in patients on tyrosine kinase inhibitor (TKI) therapy using real-time quantitative PCR is standard of care in the management of CML patients. The test utilizes a quantitative, real-time reverse transcription polymerase chain reaction (RT-qPCR) to measure BCR::ABL1 to ABL1 percent ratios on the International Scale (%IS), in t(9;22) positive CML patients during monitoring of treatment with TKIs. In this context, this study evaluated clinical performance of the Xpert® BCR-ABL Ultra assay for quantitation of BCR::ABL1 p210 transcripts. Methods The clinical performance of assay was evaluated by comparison to an RT-qPCR assay routinely used in our institution, which also detects and quantifies the mRNA transcripts for the p210 translocation types and uses the ABL gene as an endogenous control. In total, 30 fresh peripheral blood samples of CML patients with the level of BCR::ABL1 transcripts (international scale, IS) between >50% and undetectable were enrolled in this study. All steps of protocols were performed according to manufacturer ́s instructions. Results The comparison of two assay revealed consistente molecular response (MR) level. Linear regression analysis showed high correlation between the assays (R2 = 0.974, P < 0.0001) The slope of regression curve were not significantly different from the value of 1 (1.003; 95% CI, range 0.943–1.069). The evaluation of MR level was identical in 21/28 (75%) samples. Two samples were excluded from the study due to failure to control ABL1 (Ct > 18). The median of ABL1 copies per sample was 66 011 copies (range 20 010–236 171) for conventional RT-qPCR assay. Xpert BCR-ABL Ultra reports %IS (MR), but this test does not report ABL1 copy numbers. If the Xpert BCR-ABL Ultra test reports a positive or negative result and the ABL1 Ct value is below 18, a minimum of 32 000 ABL1 copy numbers is guaranteed in the reaction. The BCR::ABL1 negativity was concordant in 2/8 samples. Conclusion We showed that the results Xpert® BCR-ABL Ultra assay (MR) are in good correlation with the results of RT-qPCR conventional method.The Xpert® BCR-ABL Ultra assay simplifies the generation of results by integrating nucleic acid extraction, amplification, and quantification of the BCR::ABL1 p210 transcripts in peripheral blood specimens. The assay turn-around-time is approximately 3 h. This does not differentiate between b2a2 or b3a2 fusion transcripts.This assay is unable to detect BCR::ABL1 p190 or other rarer translocations.