Contributions
Abstract: EP661
Type: E-Poster Presentation
Session title: Chronic myeloid leukemia - Biology & Translational Research
Background
Tyrosine kinase inhibitors (TKI) cessation in patients with chronic myeloid leukemia (CML) can be currently managed in clinical practice. However, only patients with major transcript types are eligible for TKI cessation according to European LeukemiaNet recommendation as BCR-ABL1 quantification for monitoring of measured residual disease (MRD) is standardized for e13a2/e14a2 transcripts only.
Aims
The collaborative EUTOS work aimed 1) to compare DNA and mRNA data measured by qPCR and ddPCR in CML patients with atypical BCR-ABL1 transcripts and 2) to evaluate DNA/mRNA pattern in the patients in deep molecular response (DMR) and their potential eligibility for TKI stopping.
Methods
Paired peripheral blood samples from 9 patients (e19a2=5; e13a3=2; e1a2=1; e6a2=1) with median follow-up 90 months (range 20-225 months) were measured by qPCR (n=223) and ddPCR (n=188). Four patients with e19a2, 1=e13a3 and 1=e6a2 responded to TKI with sustained DMR. Patient-specific genomic BCR-ABL1 fusions were characterized by NGS. The sensitivity of DNA and mRNA analysis varied between 10-4 – 10-5. The deterministic model was applied to evaluate MRD pattern.
Results
The amount of mRNA and DNA BCR-ABL1RelDG (the quantity of BCR-ABL1 was determined in relation to the corresponding quantity in the diagnostic sample defined as 100%) highly correlated in samples collected from the start of TKI until achievement of DMR (defined as MRD at levels 10-4-10-5). Differences were found at DMR levels in 75/223 samples measured by qPCR and in 62/188 samples by ddPCR. Out of the 75 samples measured by qPCR, 60 samples were DNA quantifiable and mRNA POQR (positive outside of quantifiable range) or negative, 13 samples were DNA POQR and mRNA negative. Only 2 samples were quantifiable and POQR on mRNA and POQR and negative on DNA, respectively. By ddPCR, BCR-ABL1 was DNA quantifiable and mRNA POQR or negative in all 62 samples with discrepant levels.
A total of 203 samples were available for comparison of mRNA analysis by qPCR and ddPCR. Of these, 39 results were discordant at levels below 10-4. Of these samples, 33 were quantifiable or POQR by ddPCR and were either POQR or negative by qPCR. Six samples were negative by ddPCR while positive by qPCR. DNA BCR-ABL1 levels were concordant by both techniques in 184 of 220 samples. Of the 36 discordant samples, 27 were BCR-ABL1 quantifiable by ddPCR, while POQR or negative by qPCR.
MRD pattern of the 6 patients in DMR was double negative in 1 patient with e19a2, DNA positive/RNA negative in 3 patients (e19a2, e13a3, e6a2) and double positive in 2 patients with e19a2.
Conclusion
The observed data on BCR-ABL1 atypical transcripts are highly similar to the published data with major BCR-ABL1. DNA and mRNA BCR-ABL1 quantity in CML patients with atypical transcripts were highly concordant at levels above 10-4. The discrepancy was found at DMR levels, where majority of samples were DNA quantifiable or POQR, while POQR or negative on mRNA. ddPCR showed higher precision in DNA and mRNA detection/quantification compared to qPCR at DMR levels. According to the previously proposed traffic light stratification model of probability of treatment free remission (TFR) after TKI stop, 1 patient has high probability of TFR, 3 patients have intermediate probability and 2 patients have low probability of TFR.
We assume that TKI stopping protocols may be safe also for CML patients with atypical BCR-ABL1 transcripts, especially if precision of MRD monitoring is enhanced by using ddPCR and optionally by DNA analysis.
Support: EUTOS2018, MZCR 00023736
Keyword(s): BCR-ABL
Abstract: EP661
Type: E-Poster Presentation
Session title: Chronic myeloid leukemia - Biology & Translational Research
Background
Tyrosine kinase inhibitors (TKI) cessation in patients with chronic myeloid leukemia (CML) can be currently managed in clinical practice. However, only patients with major transcript types are eligible for TKI cessation according to European LeukemiaNet recommendation as BCR-ABL1 quantification for monitoring of measured residual disease (MRD) is standardized for e13a2/e14a2 transcripts only.
Aims
The collaborative EUTOS work aimed 1) to compare DNA and mRNA data measured by qPCR and ddPCR in CML patients with atypical BCR-ABL1 transcripts and 2) to evaluate DNA/mRNA pattern in the patients in deep molecular response (DMR) and their potential eligibility for TKI stopping.
Methods
Paired peripheral blood samples from 9 patients (e19a2=5; e13a3=2; e1a2=1; e6a2=1) with median follow-up 90 months (range 20-225 months) were measured by qPCR (n=223) and ddPCR (n=188). Four patients with e19a2, 1=e13a3 and 1=e6a2 responded to TKI with sustained DMR. Patient-specific genomic BCR-ABL1 fusions were characterized by NGS. The sensitivity of DNA and mRNA analysis varied between 10-4 – 10-5. The deterministic model was applied to evaluate MRD pattern.
Results
The amount of mRNA and DNA BCR-ABL1RelDG (the quantity of BCR-ABL1 was determined in relation to the corresponding quantity in the diagnostic sample defined as 100%) highly correlated in samples collected from the start of TKI until achievement of DMR (defined as MRD at levels 10-4-10-5). Differences were found at DMR levels in 75/223 samples measured by qPCR and in 62/188 samples by ddPCR. Out of the 75 samples measured by qPCR, 60 samples were DNA quantifiable and mRNA POQR (positive outside of quantifiable range) or negative, 13 samples were DNA POQR and mRNA negative. Only 2 samples were quantifiable and POQR on mRNA and POQR and negative on DNA, respectively. By ddPCR, BCR-ABL1 was DNA quantifiable and mRNA POQR or negative in all 62 samples with discrepant levels.
A total of 203 samples were available for comparison of mRNA analysis by qPCR and ddPCR. Of these, 39 results were discordant at levels below 10-4. Of these samples, 33 were quantifiable or POQR by ddPCR and were either POQR or negative by qPCR. Six samples were negative by ddPCR while positive by qPCR. DNA BCR-ABL1 levels were concordant by both techniques in 184 of 220 samples. Of the 36 discordant samples, 27 were BCR-ABL1 quantifiable by ddPCR, while POQR or negative by qPCR.
MRD pattern of the 6 patients in DMR was double negative in 1 patient with e19a2, DNA positive/RNA negative in 3 patients (e19a2, e13a3, e6a2) and double positive in 2 patients with e19a2.
Conclusion
The observed data on BCR-ABL1 atypical transcripts are highly similar to the published data with major BCR-ABL1. DNA and mRNA BCR-ABL1 quantity in CML patients with atypical transcripts were highly concordant at levels above 10-4. The discrepancy was found at DMR levels, where majority of samples were DNA quantifiable or POQR, while POQR or negative on mRNA. ddPCR showed higher precision in DNA and mRNA detection/quantification compared to qPCR at DMR levels. According to the previously proposed traffic light stratification model of probability of treatment free remission (TFR) after TKI stop, 1 patient has high probability of TFR, 3 patients have intermediate probability and 2 patients have low probability of TFR.
We assume that TKI stopping protocols may be safe also for CML patients with atypical BCR-ABL1 transcripts, especially if precision of MRD monitoring is enhanced by using ddPCR and optionally by DNA analysis.
Support: EUTOS2018, MZCR 00023736
Keyword(s): BCR-ABL