Comparison of molecular responses based on BCR-ABL1% (IS) results from an in-house TaqMan-based qPCR versus Xpert(®) assay in CML patients on tyrosine kinase inhibitor therapy.

OBJECTIVES

Tyrosine kinase inhibitors (TKIs) have drastically changed the prospects for chronic myeloid leukemia (CML) patients. The European LeukemiaNet (ELN) recommends molecular monitoring of BCR-ABL1 mRNA levels at distinct time points to define an optimal response, warning, or failure of treatment.

METHODS

Sixty-four follow-up peripheral blood samples from CML patients on TKI were tested by two methods. Molecular responses based on BCR-ABL1% (IS) from an Xpert(®) BCR-ABL1 Monitor assay were compared with TaqMan-based qPCR.

RESULTS

Seven samples showed 'molecularly undetectable leukaemia' by both methods (11%). In-house qPCR showed 57 BCR-ABL1+ samples; 45/57 samples (79%) were concordant for 'major molecular response' (MMR, n = 32) and 'no MMR' (n = 13) by both assays, whereas nine were BCR-ABL1 negative by Xpert(®). Identical molecular responses (i.e. 'optimal') were defined in 41 samples. Discordances seen in patients < 10 months on TKI (n = 2) had no impact on clinical management, whereas for patients >12 months on TKI, a different molecular response was defined ('warning' versus 'optimal'). Thirteen samples had 'no MMR' by both methods. 10/13 showed identical intervals (>10%(IS), 1-10%(IS) or 0·1-1%(IS)), corresponding to seven 'failures' and three 'warnings'. Discordant intervals were seen in 3/13 samples (all defined as 'failures'). Deep molecular responses (MR(4·0) or MR(5·0)) with detectable BCR-ABL1 showed some fluctuations between both methods, nevertheless, all had 'optimal' responses. 'Molecularly undetectable leukaemia' was observed more frequently by Xpert(®) (n = 16) as by our in-house assay (n = 7).

DISCUSSION

Based on current ELN recommendations, Xpert(®) BCR-ABL1 assay defines identical molecular responses as TaqMan-based qPCR BCR-ABL1% (IS) data in 98% (63/64) of samples.