Chronic Myeloid Leukemia (CML): Key Information for Patients

Based on NCCN Guidelines for Patients® — Chronic Myeloid Leukemia, 2026 (NCCN Clinical Practice Guidelines in Oncology, Version 1.2026 — July 16, 2025)

What Is CML

Chronic myeloid leukemia (CML) is a blood cancer caused by a single, specific genetic change: a piece of chromosome 9 and a piece of chromosome 22 break off and switch places. This creates an abnormal shortened chromosome 22 known as the Philadelphia (Ph) chromosome, which contains a fusion gene called BCR::ABL1.

The BCR::ABL1 gene produces an abnormal protein — a tyrosine kinase — that drives uncontrolled production of white blood cells (mainly granulocytes). This genetic change is not inherited and is not passed to children.

CML has three phases, defined by the percentage of immature white blood cells (blasts) in blood and bone marrow:

Chronic phase (CP): <15% blasts — most common at diagnosis; slowly progressive; responds well to treatment
Accelerated phase (AP): 15–29% myeloblasts, or basophils ≥20%, or persistently low platelets due to disease, or new chromosomal mutations in Ph+ cells — intermediate severity
Blast phase (BP / blast crisis): ≥30% myeloblasts (myeloid), or any increase in lymphoblasts (lymphoid) — life-threatening; most difficult to treat

The central goal of therapy is to prevent progression from chronic to blast phase.

Symptoms

Many patients with chronic phase CML have no symptoms; the disease is often found incidentally on a routine blood test. When symptoms occur, they may include:

Fatigue and weakness
Fullness or discomfort in the upper left abdomen (enlarged spleen)
Night sweats
Fever without infection
Unexplained weight loss
Easy bruising or bleeding
Bone or joint pain

In accelerated or blast phase, symptoms are more pronounced and may include rapidly enlarging spleen, bone pain, and signs of severe infection.

Diagnostic Workup

Confirming diagnosis and phase requires:

Complete blood count (CBC) with differential — typically shows markedly elevated white blood cells and/or platelets
Chemistry profile including uric acid and creatinine
Hepatitis B and C screening (before treatment)
Bone marrow aspirate and biopsy — mandatory to fully stage CML; determines phase from blast percentage and cytogenetics; must be reviewed by a hematopathologist
Karyotype — detects the Philadelphia chromosome t(9;22) and any additional chromosomal changes
FISH — sensitive confirmation of the BCR::ABL1 translocation
qPCR (IS) — quantitative PCR using the International Scale; measures the proportion of BCR::ABL1-positive cells in peripheral blood; the gold standard for both diagnosis and treatment monitoring; must be performed at an IS-certified laboratory
Mutation testing / NGS — detects BCR::ABL1 kinase domain mutations (especially T315I); required when resistance is suspected and before switching TKIs
Cardiac evaluation (ECG / echocardiogram) — relevant before starting nilotinib, dasatinib, or ponatinib
HLA typing — if allogeneic transplant is being considered

Risk Groups (Chronic Phase)

At diagnosis in chronic phase, a risk score is calculated from age, spleen size, and blood counts using one of three systems: Sokal, Hasford (EURO), or EUTOS long-term survival (ELTS). All three classify patients as low, intermediate, or high risk, which guides the initial TKI choice.

Treatment

CML is highly treatable — and in chronic phase, often manageable as a chronic condition. With appropriate therapy and strict adherence, most patients can expect near-normal life expectancy. Most require lifelong treatment.

Tyrosine kinase inhibitors (TKIs)

TKIs block the BCR::ABL1 protein and stop abnormal cell growth. All are oral medications. Six TKIs are approved for CML:

TKI	Generation	Key notes
Imatinib (Gleevec)	1st	First approved TKI; well-studied; generic available; preferred for older patients, low-risk, or significant comorbidities
Dasatinib (Sprycel)	2nd	Avoid in pulmonary disease; risk of pleural effusion; generic available
Nilotinib (Tasigna)	2nd	Avoid in cardiac disease, QT prolongation, diabetes risk; sudden deaths reported; generic available; food-unrestricted formulation available
Bosutinib (Bosulif)	2nd	Avoid in liver or GI disease; generic available
Ponatinib (Iclusig)	3rd	Preferred for T315I mutation; serious cardiovascular side effects; not first-line; requires cardiology monitoring
Asciminib (Scemblix)	STAMP inhibitor	Targets a unique site on BCR::ABL1; approved for newly diagnosed CP-CML and for T315I at higher dose; avoid in history of pancreatitis

First-line treatment by risk group:

Low risk: imatinib or generic, OR second-generation TKI (bosutinib, dasatinib, nilotinib), OR asciminib, OR clinical trial
Intermediate or high risk: preferred — second-generation TKI or asciminib; other recommended — imatinib; clinical trial always an option

Critical: drug and food interactions. Avoid grapefruit, pomegranate, star fruit, green tea extract, turmeric (curcumin), St. John's Wort, ginkgo biloba, and high-dose antioxidants. Antacids, certain cardiac/antihypertensive drugs, and antidepressants may also interact. Bring a complete list of all medications and supplements to every visit.

Never stop or skip TKI doses without your doctor's guidance. Missing doses allows CML cells to proliferate and may cause permanent drug resistance.

Monitoring — qPCR milestones

Response is measured by qPCR (IS) at 3, 6, and 12 months. Specific milestones must be reached within defined timeframes:

Milestone	Definition	Target timepoint
Early molecular response (EMR)	BCR::ABL1 (IS) ≤10%	By 3 and 6 months
Complete cytogenetic response (CCyR)	BCR::ABL1 (IS) ≤1% (no Ph+ cells)	By 12 months
Major molecular response (MMR)	BCR::ABL1 (IS) ≤0.1%	Goal after CCyR
Deep molecular response (DMR)	BCR::ABL1 (IS) ≤0.01% (MR4.0) or ≤0.0032% (MR4.5)	Prerequisite for TFR

If milestones are not met, first assess adherence and drug/food interactions. If compliance is confirmed, perform mutation testing and consider switching TKIs. Any 1-log increase in BCR::ABL1 during treatment requires prompt re-evaluation.

Treatment-free remission (TFR)

For patients who achieve a sustained deep molecular response (DMR maintained for ≥2 years on TKI), stopping TKI therapy under close monitoring is possible. This requires CML specialist consultation and patient consent. BCR::ABL1 is monitored monthly for 1 year, every 6 weeks for 1 year, then every 3 months. If BCR::ABL1 rises above 0.1%, TKI must be restarted. Most patients who restart achieve remission again.

Second-line therapy

If the first TKI fails, switch to a different TKI (not back to imatinib if imatinib failed). Mutation testing guides the choice:

T315I mutation: only ponatinib or high-dose asciminib are effective — no other TKI works against T315I
Other kinase domain mutations have varying sensitivities to different TKIs
Allogeneic transplant consultation should be initiated after two or more TKI failures

Advanced phase CML

Accelerated phase: preferred TKIs — bosutinib, dasatinib, nilotinib, or ponatinib. Goal: achieve deep remission and proceed to allogeneic HCT for long-term disease control. Clinical trial is always preferred if available.

Blast phase: a medical emergency requiring immediate treatment:

Myeloid blast phase: TKI + AML-type induction chemotherapy → allogeneic HCT in remission
Lymphoid blast phase: TKI + ALL-type induction chemotherapy → allogeneic HCT in remission
Clinical trial is always the preferred first option

Allogeneic hematopoietic cell transplant (allo-HCT)

Most chronic phase CML patients do not need a transplant. Allo-HCT is reserved for advanced phase disease, multiple TKI failures, or T315I not responding to available TKIs. Requires a matched donor; performed at specialized centers; carries serious risks including graft-versus-host disease (GVHD).

After allo-HCT, qPCR is performed every 3 months for 2 years, then every 3–6 months. If BCR::ABL1 remains detectable or rises, treatment with TKI ± donor lymphocyte infusion (DLI) is given.

Supportive Care

Common TKI side effects: fatigue, nausea, diarrhea, musculoskeletal pain, rash, fluid retention (edema), headache, low blood counts (anemia, neutropenia, thrombocytopenia). Side effects vary by drug and dose.

Drug-specific concerns:

Nilotinib: QT prolongation, cardiovascular risk, elevated blood glucose, peripheral vascular disease — ECG monitoring required
Dasatinib: pulmonary arterial hypertension, pleural effusion — pulmonary monitoring required
Ponatinib: serious arterial occlusion and thrombosis risk — ongoing cardiology involvement required
All TKIs: contraindicated in pregnancy and breastfeeding; discuss fertility preservation before starting therapy

Febrile neutropenia (fever + low white blood cells) is a medical emergency requiring immediate IV antibiotics. Patients must know in advance who to contact and where to go.

Uric acid elevation at treatment start (due to rapid cell death) can cause gout or kidney stones — allopurinol is often prescribed briefly at initiation.

Long-term cardiac surveillance: consider a cardio-oncologist, especially for patients on nilotinib or ponatinib, or those with cardiovascular risk factors.

Insurance continuity is critical: any gap in TKI supply can lead to loss of response. Notify your care team immediately if coverage issues arise.

Key Messages for Patients

CML is caused by a single specific genetic mutation (BCR::ABL1). It is not inherited and not caused by anything you did.
With appropriate targeted therapy and adherence, chronic phase CML carries near-normal life expectancy for most patients.
Taking your TKI every single day as prescribed is the single most important factor in treatment success — missed doses allow leukemia cells to grow and can cause permanent resistance.
Regular qPCR monitoring at 3, 6, and 12 months is not optional — it is how your doctor knows whether the treatment is working.
Some patients who achieve a sustained deep remission may stop therapy under monitoring (treatment-free remission) — ask your doctor if you qualify.
Never stop your TKI without your doctor's guidance, even if you feel completely well.
The T315I mutation makes most TKIs ineffective — always test for mutations before switching drugs.
Seek care at a center with CML expertise, particularly for advanced phase disease or multiple TKI failures.

Source: NCCN Guidelines for Patients® — Chronic Myeloid Leukemia, 2026 (based on NCCN Clinical Practice Guidelines in Oncology, Version 1.2026 — July 16, 2025). National Comprehensive Cancer Network® (NCCN®).

Full original document available free of charge: NCCN.org/patientguidelines

This material is for informational purposes only and does not replace consultation with a treating physician.