Within the cartridge, RNA is extracted and converted to complementary DNA (cDNA). All subsequent reactions are performed within the cartridge and the results are processed and calculated by the instrument. Four mL of whole blood is processed, added to an individual sample cartridge and loaded onto the GeneXpert machine. The assay is performed using an automated platform, GeneXpert (Cepheid). The majority of CML patients show similar BCR/ABL1 mRNA levels in blood and bone marrow drawn at the same time, although occasional, patients may exhibit a difference in concurrent blood and marrow levels for technical or biological reasons, requiring follow-up testing to resolve. Because a single fusion DNA allele can produce many mRNA transcripts, the values are not directly comparable and FISH results are not applicable to the IS or to disease monitoring.īlood is the specimen of choice for monitoring CML patients. FISH measures DNA alleles and RT-PCR-based assays measure mRNA transcripts. The results of this assay cannot be directly compared with BCR/ABL1 results obtained using FISH technology. Monitoring should be performed using the same method and laboratory for each subsequent specimen. In general, the results of this assay cannot be directly compared with results generated from other PCR assays, including identical assays performed in other laboratories. If the results are being used to make major therapeutic decisions, significant changes during monitoring should be verified with a subsequent specimen. For example, if a result is given as 0.1% BCR/ABL1:ABL1, then any result between 0.05% and 0.5% should be considered essentially equivalent. Only level changes above 0.5 log should be considered clinically significant. The precision of this assay at low BCR/ABL1 levels is more variable, such that inter-run variation can be as high as + or - 0.5 log. This test should not be used to screen for BCR/ABL1 fusions at the time of diagnosis if a diagnostic screen for BCR-ABL1 transcripts is desired, the test BADX / BCR/ ABL1, Qualitative, Diagnostic Assay, which is designed to detect all reported common and rare BCR-ABL1 mRNA fusion variants, should be ordered for this purpose. If the patient is known to carry an e1/a2 (p190) fusion form, the test BA190 / BCR/ ABL, p190, mRNA Detection, Reverse Transcription-PCR (RT-PCR), Quantitative, Monitoring Assay should be used for monitoring. Other fusion forms are not detected, including those containing the BCR e1 exon, which codes for the p190 protein commonly found in acute lymphoblastic leukemia (ALL). This test detects only the e13/a2 and e14/a2 fusion forms, which code for the p210 protein. This test detects the BCR/ABL1 mRNA fusion forms found in CML (e13/a2 and e14/a2). Quantitative reverse-transcription PCR (qRT-PCR) is the most sensitive method for monitoring BCR-ABL1 levels during treatment. Monitoring the level of BCR/ABL1 mRNA in CML patients during treatment is helpful for both prognosis and management of therapy.(1-3) Rising BCR/ABL1 mRNA levels following attainment of critical therapeutic milestones (see Clinical References) can be indicative of acquired resistance mutations involving the ABL1 portion of the BCR/ABL1 fusion gene. The p210 fusion protein is an abnormal tyrosine kinase known to be critical for the clinical and pathologic features of CML, and agents that block the tyrosine kinase activity (ie, tyrosine kinase inhibitors or TKI, such as imatinib mesylate) have been used successfully for treatment. The e13/a2 and e14/a2 fusion forms produce a 210-kDa protein (p210). This fusion is designated BCR/ABL1 and may be seen on routine karyotype as the Philadelphia chromosome.Īlthough various breakpoints within the BCR and ABL1 genes have been described, more than 95% of CMLs contain a consistent mRNA transcript in which either the BCR exon 13 (e13) or BCR exon 14 (e14) is fused to the ABL1 exon 2 (a2), yielding fusion forms e13/a2 and e14/a2, respectively. CML is consistently associated with fusion of the breakpoint cluster region gene ( BCR) at chromosome 22q11 to the Abelson gene ( ABL1) at chromosome 9q23. Chronic myeloid leukemia (CML) is a hematopoietic stem cell neoplasm included in the broader diagnostic category of myeloproliferative neoplasms.
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