Evaluation of Cepheid Xpert® BCR-ABL Monitor Assay in Three Italian Reference Centers for Monitoring of BCR-ABL Transcript Levels in CML Patients

Effective management of tyrosine kinase inhibitor (TKI) therapy for patients with CML requires frequent patient testing to monitor patient disease status. The gold standard for this testing is a PCR measurement of the BCR-ABL/ABL transcript ratio. Hence, standardized, accurate and reproducible molecular analyses are fundamental for clinicians in order to correctly address therapeutic decision and to achieve a better patient management. Based on these clinical needs, it is widely recognized that inter-laboratory reproducibility is a crucial issue that requires standardization and strict alignment of BCR-ABL values on the international scale (IS), as established by the International Randomized Study of Interferon and STI571 (IRIS) laboratories. In addition to this, another important aspect in terms of patient management is the availability of a rapid response, improving patient quality of life by reducing anxiety linked to delay in results delivery.

Xpert® BCR-ABL Monitor, developed and manufactured by Cepheid (Sunnyvale, CA), is a cartridge-based automated assay for quantification of BCR-ABL1 mRNA, reporting results in International Scale (IS). Alignment to the IS, based upon the quality control standards derived from the WHO BCR-ABL Standards, is performed lot to lot automatically by the software of the Cepheid GeneXpert® DX Instrument.

Xpert® BCR-ABL Monitor automates and integrates sample processing, nucleic acids extraction and amplification and target sequence detection in peripheral blood specimens collected either in EDTA or PAXgene tubes using real-time RT-PCR. The cartridge includes reagents to detect BCR-ABL fusion genes resulting from two major breakpoints, translocation e13a2 (b2a2) and e14a2 (b3a2) and the ABL transcript as an endogenous control.

In the following study, Xpert® BCR-ABL Monitor was independently evaluated in the three Italian reference centers for BCR-ABL mRNA monitoring of the LabNet project. A total of 150 peripheral blood samples from CML patients, equally divided between centers, were analyzed both with the standard laboratory method and with Xpert® BCR-ABL Monitor Assay, in order to compare the results expressed in International Scale. BCR-ABL mRNA of the specimens covered a broad IS range, allowing to compare data also at low levels of disease (MR 4.5, 0.00316% BCR-ABL/ABL).

Overall, linear regression demonstrated that there was a good correlation between Xpert® BCR-ABL Monitor and reference centers data (R²= 0.92). Correlation slightly increased when the data produced with Xpert® BCR-ABL Monitor were refined using a correction tool not automatically adopted by the current version of the assay software (R²= 0.93). Moreover, using assay comparison criteria proposed by Müller et al. (Leukemia 2009), Xpert® BCR-ABL Monitor was considered comparable to the standard laboratory methods of the reference centers, considering that all the three acceptance criteria were satisfied (58% of the samples between 0.5 and 2-fold variation, 78% of the samples between 0.33 and 3-fold variation, 91% of the samples between 0.2 and 5-fold variation).

In conclusion, Xpert® BCR-ABL Monitor demonstrated to be a rapid, reliable and accurate test for monitoring of BCR-ABL mRNA transcript levels. Results were available within approximately 2 hours, potentially allowing clinicians to report results to patient the same day of the visit. From the technical point of view, cartridge-based automated system significantly reduced operator hands-on time from several hours to approximately 15 minutes.

Concerning the assay comparative performance, Xpert® BCR-ABL showed to have a good inter-laboratory reproducibility, with no significant differences between the three reference centers standard methods.

Acknowledgments: ELN, AIL, AIRC, PRIN, progetto Regione-Università 2010-12 (L. Bolondi), FP7 NGS-PTL project.