Standardization of the BCR-ABL1 Quantification in CML
When using molecular tests to quantify BCR-ABL1 in CML patients, it is recommended that the test be performed in a standardized laboratory. Standardization ensures that results comply with the ELN (European LeukemiaNet; Baccarani et al., Blood 2013) guidelines, enables comparisons to be made between laboratories and serves as quality assurance. MLL has been determining the standard value of BCR-ABLIS (IS = International Scale) since 2011.
Thanks to improved therapeutic options and the availability of specific targeted tyrosine kinase inhibitors (TKI) of BCR-ABL1 , the survival rate of patients' is increasing, which necessitates a more precise follow-up to detect any residual disease. That is why quantitative real-time PCR, which provides a sensitivity of up to 10-5 (1 in 100,000), is used in molecular genetics.
The molecular responses of TKI therapy have been defined by Cross et al. (Leukemia 2015) and expand on existing criteria. This publication, clearly defines the criteria for attributing individual Molecular Response (MR) stages (MR4, MR4.5, MR5) based on the quantification result. The prerequisite for this is the measurement of BCR-ABLIS. This value is calculated by multiplying the percentage value of BCR-ABL1/ABL1 (measurable BCR/ABL1 copies relative to the ABL1 reference gene) by the laboratory-specific conversion factor. This conversion factor is re-determined each year during the quality assurance round.
In the last 9 years, MLL has taken part in various laboratory comparisons for quality assurance and for determining the conversion factor for BCR-ABL1 quantification. Since 2015, the tests for selected laboratories have been performed by the EUTOS association (European Treatment and Outcome Study). The objective is to make CML diagnostics more reliable by standardizing them across Europe. To do this, a network of 48 laboratories have been established in 27 European countries (Cross et al., Leukemia 2016). The MLL is one of these laboratory, and the result of its annual quality comparison is indicated on the issued certificate. There are currently five EUTOS certified laboratories in Germany.
Good to know: Standardization is currently limited to the most common BCR-ABL1 transcript variants e13a2 and e14a2 (approx. 98% of all CML patients). The transcript variant should therefore be determined at diagnosis in order to ensure sound monitoring of minimal residual disease during therapy and to provide a BCR-ABLIS value.
References
Baccarani M et al. European LeukemiaNet recommendations for the management of chronic myeloid leukemia: 2013. Blood. 2013 Aug 8;122(6):872-84.
Cross NC et al. Laboratory recommendations for scoring deep molecular responses following treatment for chronic myeloid leukemia. Leukemia 2015 ;29(5):999-1003.
Cross NC et al. Development and evaluation of a secondary reference panel for BCR-ABL1 quantification on the International Scale. Leukemia. 2016 Sep;30(9):1844-52.