# BCR::ABL1 transcript (Philadelphia chromosome, quantitative PCR)

Source: https://onco.cc/biomarkers/bcr-abl1-transcript/  
OnCo record `bcr-abl1-transcript` (Biomarker). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The BCR::ABL1 fusion is the Philadelphia chromosome that defines chronic myeloid leukaemia and some acute lymphoblastic leukaemia. Its transcript level in blood, on the international scale, is how response to tyrosine kinase inhibitors is measured and when treatment can be stopped.

## Summary

The t(9;22) translocation is confirmed at diagnosis by karyotype, FISH or PCR; thereafter quantitative RT-PCR of BCR::ABL1 mRNA on the International Scale defines response milestones (early molecular response <= 10 percent at 3 months, major molecular response <= 0.1 percent, MR4 <= 0.01 percent, MR4.5 <= 0.0032 percent) under ELN and NCCN. Imatinib, dasatinib, nilotinib, bosutinib, ponatinib and asciminib are labelled for Ph+ CML; the MRDx BCR-ABL Test (MolecularMD) is on the FDA list as the companion for nilotinib's treatment-free remission labelling (K173492, 2017), which requires sustained deep molecular response before stopping.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: BCR-ABL1; BCR::ABL1; BCR-ABL; Philadelphia chromosome positive; Ph+; Ph-positive; BCR-ABL1 IS; BCR-ABL1 international scale; MMR; MR4; MR4.5; major molecular response
- Tags: biomarker; cml

## Sources

- Gleevec prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=211ef2da-2868-4a77-8055-1cb2cd78e24b
- FDA: List of FDA-Authorized Companion Diagnostic Devices: https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools

## Connected records

- biomarkers: [BCR::ABL1 T315I](https://onco.cc/biomarkers/bcr-abl1-t315i/)
- cancers: [Acute lymphoblastic leukaemia](https://onco.cc/cancers/all-leukemia/), [Chronic myeloid leukaemia (CML)](https://onco.cc/cancers/cml/), [Chronic myeloid leukaemia, accelerated and blast phase](https://onco.cc/cancers/cml-advanced-phase/), [Chronic myeloid leukaemia, chronic phase](https://onco.cc/cancers/cml-chronic-phase/), [Philadelphia chromosome-positive acute lymphoblastic leukaemia in children (Ph-positive ALL)](https://onco.cc/cancers/all-paediatric-ph-positive/)
- drugs: [Asciminib](https://onco.cc/drugs/asciminib/), [Bosutinib](https://onco.cc/drugs/bosutinib/), [Dasatinib](https://onco.cc/drugs/dasatinib/), [Imatinib](https://onco.cc/drugs/imatinib/), [Nilotinib](https://onco.cc/drugs/nilotinib/), [Ponatinib](https://onco.cc/drugs/ponatinib/)
- terms: [Minimal / molecular residual disease (MRD)](https://onco.cc/terms/mrd/), [Molecular response (MMR, MR4, treatment-free remission)](https://onco.cc/terms/molecular-response/), [Philadelphia chromosome (Ph+, BCR::ABL1)](https://onco.cc/terms/philadelphia-chromosome/)
- targets: [BCR::ABL1 (Philadelphia chromosome)](https://onco.cc/targets/bcr-abl/)

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