Chronic Myeloid Leukemia (CML)

CML is a blood cancer arising from a bone marrow stem cell that acquires the Philadelphia chromosome — a translocation between chromosomes 9 and 22 that creates the BCR-ABL1 fusion gene. BCR-ABL1 produces a constitutively active tyrosine kinase that drives unchecked myeloid cell proliferation. It accounts for approximately 15% of all leukaemias in adults, with a median age at diagnosis of around 55 years. Unlike many cancers, CML has no significant hereditary predisposition; the Philadelphia chromosome arises as a somatic (non-inherited) event. Ionising radiation is the only well-established environmental risk factor.

CML and CLL are entirely different diseases. CML arises from a myeloid stem cell and is defined by the Philadelphia chromosome BCR-ABL1 fusion gene; it is a myeloproliferative neoplasm progressing through chronic, accelerated, and blast phases. CLL arises from a mature B-lymphocyte clone and is a lymphoid malignancy driven by different molecular events (del(17p)/TP53, IGHV status, BTK pathway). Treatment is completely different: CML uses BCR-ABL1 tyrosine kinase inhibitors (imatinib, dasatinib, asciminib); CLL uses BTK inhibitors and venetoclax. They are unrelated conditions that happen to share the 'chronic leukaemia' label.

BCR-ABL1 quantitative RT-PCR measures the level of abnormal BCR-ABL1 mRNA transcripts in peripheral blood relative to a reference control gene. The result is expressed as a percentage on the International Scale (IS) — for example, 10% IS at diagnosis, 0.1% IS at Major Molecular Response (MMR). The IS allows results from different laboratories worldwide to be compared on a standardised scale. A lower percentage means less disease is detectable: below 0.1% IS is MMR; below 0.01% IS is MR4.0; below 0.0032% IS is MR4.5 — the deep response required for treatment-free remission attempts.

The T315I mutation is a substitution at position 315 in the BCR-ABL1 kinase domain — the 'gatekeeper' residue that imatinib, dasatinib, nilotinib, and bosutinib all require to bind effectively. T315I changes this residue so that all first- and second-generation TKIs can no longer bind and inhibit BCR-ABL1. Only two agents retain meaningful activity against T315I: ponatinib (a third-generation TKI) and asciminib at its higher 200 mg twice-daily dose (which binds a completely different site on BCR-ABL1). T315I testing by ABL1 mutation analysis at TKI failure is therefore essential before selecting the next treatment.

CML is not considered cured by TKI therapy alone in conventional terms, but treatment-free remission (TFR) — stopping TKI and maintaining undetectable disease — is achievable in approximately 50% of patients who sustain deep molecular response (MR4.0/MR4.5) for at least two years on TKI. Patients who successfully achieve TFR can potentially live without medication for many years. Allogeneic stem cell transplantation remains the only therapy considered potentially curative at a biological level, but it is reserved for blast crisis and multi-TKI-resistant disease given its associated morbidity and mortality.

Treatment-free remission (TFR) refers to safely stopping TKI therapy after achieving and sustaining a deep molecular response. ELN 2020 eligibility criteria include: chronic phase CML only; at least 3 years on TKI therapy; sustained MR4 (BCR-ABL1 ≤0.01% IS) or deeper for at least 2 consecutive years; access to monthly BCR-ABL1 IS monitoring during TFR; and a shared decision-making conversation about the approximately 40–50% risk of molecular relapse requiring TKI restart. Blast or accelerated phase, T315I mutation, and prior allo-SCT are among factors that affect TFR candidacy. All TFR attempts should be managed at or in close coordination with a specialist CML centre.

Blast crisis (≥20% blasts in blood or bone marrow) is the most serious complication of CML, where the disease transforms to behave like acute leukaemia. It requires immediate specialist haematology evaluation. Management depends on blast lineage: myeloid blast crisis is treated with AML-type induction combined with a TKI active against the resistance mutation present; lymphoid blast crisis is treated with ALL-type regimens (TKI + steroids + vincristine) given the B-lymphoid immunophenotype. The goal is to re-achieve chronic phase, followed by allogeneic stem cell transplantation in eligible patients who have a donor and adequate performance status.

Yes — active CML clinical trials include first-line asciminib (ASC4FIRST), low-dose ponatinib optimisation for T315I disease (OPTIC), TKI + pegylated interferon-alpha for deeper TFR rates (TIGER), and BCL2 inhibitor venetoclax combinations targeting CML stem cells. For multi-TKI-resistant and compound-mutation CML, investigational BCR-ABL1 PROTACs and bi-allosteric inhibitors are entering Phase 1/2 trials. Patients with T315I disease, blast crisis, or compound mutations who have exhausted standard options are the strongest candidates for clinical trial enrolment.

Yes. CancerFax supports CML patients by reviewing BCR-ABL1 IS results, cytogenetics, and ABL1 kinase domain mutation reports, coordinating specialist CML haematology second opinions, and identifying access pathways to second- and third-generation TKIs including asciminib and ponatinib for T315I-mutated and multi-resistant CML.

For patients facing blast crisis or requiring allogenic SCT, CancerFax can help identify specialist transplant centres and assist with coordination of the complex multi-step pathway. For patients in regions where asciminib or ponatinib are not accessible locally, CancerFax coordinates access to specialist haematology centres in China and internationally.