The short answer
Chronic myeloid leukemia is sorted first by phase, using the share of blasts in blood and marrow. Most people are in chronic phase and start a daily tablet at home. After that, a single blood test called BCR::ABL1 tracks how well it is working.
Phase comes first. Chronic phase means under 10 percent blasts and promyelocytes, accelerated phase 10 to 19 percent, and blastic phase 20 percent or more.
NCI says the 10-year event-free and overall survival rates exceed 90 percent with any of the approved first-line tyrosine kinase inhibitors.
Response is tracked by BCR::ABL1 in the blood. A major molecular response means a level of 0.1 percent or less.
Most people do not need a bone marrow test at diagnosis, and drug choice often turns on side effects, other health problems, and cost.
Choose how you want to understand this
The full explanation.
Phase comes before everything else
CML is not staged the way a solid tumour is. It is placed in one of three phases, and the dividing line is the share of blasts, meaning immature cells, in the blood or marrow.
- Chronic phase: under 10 percent blasts and promyelocytes.
- Accelerated phase: 10 to 19 percent blasts.
- Blastic phase: 20 percent or more blasts.
NCI adds one more term. When 20 percent or more blasts appear alongside fever, malaise, and a spleen that keeps growing, that is blast crisis.
Most people are found in chronic phase. Ask for your exact percentage, because the whole plan follows from it.
The 2026 figures of 9,650 new US cases and 1,170 deaths are American Cancer Society projections, carried on SEER's stat facts page rather than counted by SEER. SEER's own measured numbers are a median age at diagnosis of 67 and five-year relative survival of 71.1 percent for 2016 through 2022.
What the first workup does and does not include
An enlarged spleen is the most common finding on examination. It can be huge, filling much of the abdomen, or barely noticeable. In about 10 percent of people the spleen is neither felt nor enlarged on a scan.
Other early symptoms are fatigue, unexplained weight loss, drenching night sweats, and fever.
The core tests are a blood count with differential, blood chemistry, chromosome analysis, and a look for the BCR::ABL1 rearrangement using FISH or PCR. PCR is the most sensitive method available, and a small group of people only show the rearrangement that way.
A bone marrow test is not automatic. NCI says most people do not need one. It becomes appropriate with fever, malaise, a rapidly enlarging spleen, or more than 10 percent blasts in the blood.
A daily tablet, and why the choice is not obvious
Treatment for chronic-phase CML uses a drug that blocks the BCR::ABL1 protein. NCI lists five that can be used first: asciminib, nilotinib, dasatinib, bosutinib, and imatinib. With any of them, the 10-year event-free and overall survival rates exceed 90 percent. That figure comes from people enrolled in trials, which is why it sits well above the SEER population number.
So the choice is rarely about which one works. It is about which one suits you.
Nilotinib carries a boxed warning for QT prolongation and sudden deaths, so heart rhythm and blood minerals are checked before and during treatment. Dasatinib can cause fluid around the lungs, and a trial found that halving the usual daily amount worked about as well while cutting these effusions from 21 percent to 5 percent. If that applies to you, your haematologist decides it — never halve a tablet on your own. Asciminib works at a different spot on the protein and reached a major molecular response at 48 weeks in 67.7 percent of people, against 49 percent for the comparison group. Its first-line approval is an accelerated one, based on that response rate rather than on survival.
Cost is a real part of this conversation, and NCI says so plainly. It puts asciminib at about $260,000 a year in 2024 and imatinib at about $500. Ask what your plan actually covers.
One practical point is easy to miss. Weight-loss surgery can interfere with absorbing these tablets, which may weaken the response.
The number you will live by
Response is measured by how much BCR::ABL1 is left in your blood, reported as a percentage.
A level of 10 percent or less at three months predicts the best outcome. NCI cautions against switching drugs on that number alone, since 75 percent of people with a slower start still do well. After a year, the preferred target is a major molecular response, meaning 0.1 percent or less. A deep molecular response is 0.01 percent or less.
Untreated, chronic phase does not stay chronic. NCI puts the rate of progression to blast crisis at 5 to 10 percent in the first two years and 20 percent in later years. That is the reason for taking the tablet daily and keeping the blood tests.
Can you ever stop?
Sometimes, and it is a genuine question to raise, not a fantasy.
NCI describes the best candidates as people who have taken a tyrosine kinase inhibitor for more than 3 to 5 years and reached a deep molecular response. About half of those who stop will relapse. Among people who held a deep response for five years or more, one analysis found a relapse rate near 10 percent.
Almost everyone who relapses responds again to the same drug. Stopping still requires close monitoring, at least every three months, because relapses have appeared two to three years later. Some people get muscle and joint pain after stopping.
When to get help sooner
- Call 911 or go to an emergency department if you faint, feel your heart thumping irregularly, or get chest discomfort while taking nilotinib. Its label carries a boxed warning for QT prolongation and sudden deaths, so this is not a symptom to sit on.
- Call 911 or go to an emergency department if breathing becomes difficult at rest, or pain under your left ribs turns severe and sudden. A very large spleen can bleed.
- Call your care team straight away, day or night, if your temperature passes 100.4°F (38°C), or chills start. A fever while on treatment is handled as an emergency, so if you cannot reach the team quickly, get to an emergency department and tell them you are being treated for leukaemia. On dasatinib, breathlessness may instead be fluid gathering around a lung, so mention which drug you are on.
- Call your care team the same day if you have new bone pain, bruising you cannot account for, or bleeding that keeps going.
- Call your care team within a day or two if vomiting or diarrhoea stops you keeping your tablet down. Missed doses matter here, because response is measured by how far the BCR::ABL1 level falls.
- Call your care team within a day or two if fullness on the left side under the ribs is growing week by week, or night sweats and unplanned weight loss return.
Related pages
Chronic Myeloid Leukemia (CML), What Does BCR-ABL Mean on a Report?, What Does FISH Test Mean in Cancer?, and What Is Targeted Therapy?.
Sources
Words to know
Tap any term to see what it means.
Common questions
Do I need a bone marrow biopsy?
Often not. NCI says most people with CML do not require a bone marrow examination. It is appropriate when there is fever, malaise, a rapidly enlarging spleen, or more than 10 percent blasts in the blood.
Which tyrosine kinase inhibitor is best?
NCI says the preferred first treatment could be any of asciminib, nilotinib, dasatinib, bosutinib, or imatinib. The newer drugs reach a major molecular response sooner, but it is not yet clear that this changes long-term results.
Will I take this forever?
Maybe not. NCI describes stopping as an option for people who have taken a tyrosine kinase inhibitor for more than 3 to 5 years and reached a deep molecular response. About half relapse after stopping, and almost all of them respond again to the same drug.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Your next step
Turn this topic into questions for your next appointment.
Speak With Trained Specialists & Human Navigators
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Immediate emergency guidance for fever (>100.4°F during chemo), severe pain, or shortness of breath.
Help Us Improve This Guide
Did this explanation answer your question and help you determine your next step?
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Knowledge Check
0 of 3 answered
This self-assessment checks understanding of educational content only. It is not medical advice.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Sources last checked: 2026-08-13 what this meansLast updated: 2026-08-19Next planned review: 2027-07-20
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source checked. This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.
Related articles
Still have questions?
Educational answers, plain language
Free to print and share