Contributions
Abstract: PB1829
Type: Publication Only
Background
Detection of BCR-ABL1 e13a2 or e14a2 transcripts (major breakpoint, M-BCR) of translocation t(9;22) (also known as the Philadelphia chromosome) is important in CML monitoring tumor burden. The International Scale (IS) was established to standardize reporting relative to a common baseline. As newer TKI therapies create deeper responses, analytical sensitivity has become a critical topic in investigations into TKI discontinuation, where researchers require a clinically validated assay that calls a molecular reduction (MR) of ≥4.5 logs below baseline (i.e. MR4.5 or 0.0032%IS).
Aims
To clinically validate the QuantideX qPCR BCR-ABL1 IS Kit and to reaffirm the clinical utility of BCR-ABL1 RT-qPCR monitoring in patients with t(9;22) positive CML, a correlation between molecular response (MR) values and long-term outcome was determined.
Methods
The QuantideX qPCR BCR-ABL IS Kit uses standard TaqMan chemistry to quantitate BCR-ABL1 and the ABL1 reference gene. Associated software reports an international scale BCR-ABL1 value and a log-transformed MR value, with a 3 log-reduction from pre-treatment baseline represented as 0.1%IS or MR3.0. Three laboratories performed BCR-ABL1 testing on banked RNA specimens from 96 chronic phase CML patients from 2 hospitals drawn 12-18 months after starting TKI therapy. Clinical events (TKI therapy change, loss of complete hematologic or cytogenetic response, progression to accelerated phase or blast crisis, kinase domain mutation, or death) were recorded through 36±4 months after starting TKI. Two operators per site also tested serially-diluted reproducibility samples (range MR1.0 to MR4.0) in multiple replicates over 5 days. The 95% LOD for the assay was defined as the median measured %IS value of 4 analogous serially-diluted specimens.
Results
51 patients had MR<3.0 at 12-18 months post-TKI. Of these 51 patients who did not achieve a major molecular response (MMR), 20 had a subsequent clinical event, 17 had no event, and 14 were lost to follow-up (LFU). 45 patients had MR≥3 at 12-18 months post-TKI. Of these 45 patients who did achieve MMR, 8 had an event, 28 had no event, and 9 were LFU. Kaplan-Meier survival curves demonstrated a 22% prolongation of event-free survival (95% CI 2%>42%) at 3 years between the two MR groups [p=0.028; 58% (95% CI 44%>75%) for MR<3 vs 80% (95% CI 68%>93%) for MR≥3)]. Specimens with MR values ranging from MR1 to MR4 showed an average %CV of 2.6%. Day to day agreement was high with MR SD by operator ranging from 0.000 to 0.060. Site to site agreement was high with MR SD by site ranging from 0.000 to 0.069. The 95% LOD for both transcripts (e13a2 & e14a2) was MR4.7 (0.002%IS), allowing sensitive detection of the MR4.5 cutoff that defines “complete molecular response” in ongoing treatment-free remission clinical trials.
Conclusion
The QuantideX qPCR BCR-ABL IS Kit has excellent reproducibility and analytical sensitivity, and the achievement of MR>3 (major molecular response) by this assay predicts prolonged event-free survival in TKI-treated CML patients.
Session topic: 8. Chronic myeloid leukemia - Clinical
Keyword(s): Chronic myeloid leukemia, RT-PCR, Monitor, Clinical Trial
Abstract: PB1829
Type: Publication Only
Background
Detection of BCR-ABL1 e13a2 or e14a2 transcripts (major breakpoint, M-BCR) of translocation t(9;22) (also known as the Philadelphia chromosome) is important in CML monitoring tumor burden. The International Scale (IS) was established to standardize reporting relative to a common baseline. As newer TKI therapies create deeper responses, analytical sensitivity has become a critical topic in investigations into TKI discontinuation, where researchers require a clinically validated assay that calls a molecular reduction (MR) of ≥4.5 logs below baseline (i.e. MR4.5 or 0.0032%IS).
Aims
To clinically validate the QuantideX qPCR BCR-ABL1 IS Kit and to reaffirm the clinical utility of BCR-ABL1 RT-qPCR monitoring in patients with t(9;22) positive CML, a correlation between molecular response (MR) values and long-term outcome was determined.
Methods
The QuantideX qPCR BCR-ABL IS Kit uses standard TaqMan chemistry to quantitate BCR-ABL1 and the ABL1 reference gene. Associated software reports an international scale BCR-ABL1 value and a log-transformed MR value, with a 3 log-reduction from pre-treatment baseline represented as 0.1%IS or MR3.0. Three laboratories performed BCR-ABL1 testing on banked RNA specimens from 96 chronic phase CML patients from 2 hospitals drawn 12-18 months after starting TKI therapy. Clinical events (TKI therapy change, loss of complete hematologic or cytogenetic response, progression to accelerated phase or blast crisis, kinase domain mutation, or death) were recorded through 36±4 months after starting TKI. Two operators per site also tested serially-diluted reproducibility samples (range MR1.0 to MR4.0) in multiple replicates over 5 days. The 95% LOD for the assay was defined as the median measured %IS value of 4 analogous serially-diluted specimens.
Results
51 patients had MR<3.0 at 12-18 months post-TKI. Of these 51 patients who did not achieve a major molecular response (MMR), 20 had a subsequent clinical event, 17 had no event, and 14 were lost to follow-up (LFU). 45 patients had MR≥3 at 12-18 months post-TKI. Of these 45 patients who did achieve MMR, 8 had an event, 28 had no event, and 9 were LFU. Kaplan-Meier survival curves demonstrated a 22% prolongation of event-free survival (95% CI 2%>42%) at 3 years between the two MR groups [p=0.028; 58% (95% CI 44%>75%) for MR<3 vs 80% (95% CI 68%>93%) for MR≥3)]. Specimens with MR values ranging from MR1 to MR4 showed an average %CV of 2.6%. Day to day agreement was high with MR SD by operator ranging from 0.000 to 0.060. Site to site agreement was high with MR SD by site ranging from 0.000 to 0.069. The 95% LOD for both transcripts (e13a2 & e14a2) was MR4.7 (0.002%IS), allowing sensitive detection of the MR4.5 cutoff that defines “complete molecular response” in ongoing treatment-free remission clinical trials.
Conclusion
The QuantideX qPCR BCR-ABL IS Kit has excellent reproducibility and analytical sensitivity, and the achievement of MR>3 (major molecular response) by this assay predicts prolonged event-free survival in TKI-treated CML patients.
Session topic: 8. Chronic myeloid leukemia - Clinical
Keyword(s): Chronic myeloid leukemia, RT-PCR, Monitor, Clinical Trial