BCR/ABL Quantitative PCR

Function

The BCR-ABL1 quantitative test measures the amount of the BCR-ABL1 fusion transcript in the blood or bone marrow. This transcript is the product of the 'Philadelphia Chromosome,' a translocation between chromosomes 9 and 22, which is the hallmark of Chronic Myeloid Leukemia (CML) and some cases of Acute Lymphoblastic Leukemia (ALL).

Why it is Ordered

This test is primarily used to monitor the response to treatment with Tyrosine Kinase Inhibitors (TKIs), such as imatinib, dasatinib, or nilotinib. It is the most sensitive tool for measuring 'Minimal Residual Disease' (MRD).

Interpreting the International Scale (IS)

Results are expressed as a percentage on the International Scale (IS).

• Major Molecular Response (MMR): Defined as a BCR-ABL1/ABL ratio of ≤ 0.1% on the IS.
• Deep Molecular Response (DMR): Ratios of ≤ 0.01% (MR4.0) or ≤ 0.0032% (MR4.5). Achieving DMR is a prerequisite for considering treatment-free remission (TFR).

Clinical Utility

Monitoring occurs every 3 months during initial treatment. A rising level of BCR-ABL1 transcripts can indicate a loss of response, poor medication adherence, or the development of kinase domain mutations that cause drug resistance.