CML Symptoms: Common Signs, and Why Many People Have None

Chronic myeloid leukemia can arrive with no symptoms at all. NCI's health-professional summary puts it plainly: CML may present without symptoms. Treatment usually starts at diagnosis. And that diagnosis rests on four things. An elevated white blood cell count. An enlarged spleen. A high platelet count. And identification of the BCR::ABL1 translocation.

Notice what is not on that list. No symptom is required. A person can feel entirely well and still have a blood count that tells the story.

CML is not rare, but it is not common either. For 2026 the American Cancer Society projects 9,650 new US cases and 1,170 deaths; SEER Stat Facts publishes that projection, and NCI's PDQ summary is still carrying the 2025 version of it. The median age of people with Philadelphia chromosome-positive CML is 67 years.

Splenomegaly means an enlarged spleen. It is the most common finding on physical examination at the time of diagnosis. The range is remarkable. The PDQ describes a spleen that may be enormous, filling most of the abdomen. That causes pain or a feeling of fullness, and is a real clinical problem in itself. Or the spleen may be only slightly enlarged.

And in about 10% of patients, the spleen cannot be felt at all, and is not enlarged on a CT scan. So a normal-feeling belly rules nothing in or out.

That is why spleen size gets measured and recorded rather than described loosely. It is one of the few physical signs that tracks the disease.

Beyond the spleen, the PDQ lists four presenting symptoms:

• Fatigue
• Unexplained weight loss
• Drenching night sweats
• Fever

Every one of those has more common explanations. Fatigue and night sweats belong to dozens of ordinary conditions. What separates CML is not the symptom pattern. It is the blood count. No symptom list substitutes for a complete blood count with differential.

CML is a disease of overproduction, and the bone marrow shows it. The marrow is hypercellular, meaning packed with cells. The myeloid series shifts toward immature forms. Eosinophils or basophils are often increased. So are megakaryocytes, the cells that make platelets. When the platelet count is very high, fragments of their nuclei can turn up in the blood. The myeloid-to-erythroid ratio is usually greatly raised, and the percentage of lymphocytes is reduced. One lab quirk is distinctive. The leukocyte alkaline phosphatase enzyme is absent, or markedly reduced, in CML neutrophils.

The shift toward immature cells is the bridge to symptoms. A high total white count does not mean a working immune system. And as the marrow fills with the wrong cells, red cells and platelets can fall. That produces tiredness from anemia, and easy bruising from a low platelet count.

CML has three phases. Each has a numeric definition, based on the share of blasts in the blood or marrow. Blasts are immature cells.

• Chronic phase: under 10% blasts and promyelocytes in the peripheral blood and bone marrow.
• Accelerated phase: 10% to 19% blasts in the peripheral blood or bone marrow.
• Blastic phase: 20% or more blasts in the peripheral blood or bone marrow.

Blast crisis is a further step: 20% or more blasts together with fever, malaise, and progressive splenomegaly.

The move between phases may happen gradually over a year or more. It may also happen abruptly. Rates matter here. Progression from chronic phase to blast crisis runs 5% to 10% in the first 2 years, and 20% in later years. Four factors predict a shorter chronic phase on tyrosine kinase inhibitor treatment. Older age. Cytogenetic abnormalities in addition to the Philadelphia chromosome. A higher share of blasts in blood or marrow. And anemia.

Our page on CML phases covers how those categories are tracked over time.

This is the part worth remembering. It is the one thing symptoms are genuinely good for. The PDQ names specific signs of progression.

Signs that indicate a change to accelerated-phase CML:

• Progressive splenomegaly — a spleen that keeps getting bigger.
• Increased leukocytosis, or thrombocytosis, or both — rising white cell or platelet counts.
• Progressive anemia.

Signs that indicate a change to blast crisis, on top of the accelerated-phase signs:

• Thrombocytopenia — a falling platelet count.
• Increasing and painful splenomegaly, or an enlarging liver.
• Fever.
• Bone pain.
• Development of destructive bone lesions.

Note where bone pain sits on that list. It is not a typical first symptom of chronic-phase CML. The PDQ places it among the blast-crisis signs. So new bone pain in someone with known CML is worth reporting promptly, rather than filing under aches and pains.

Fever changes the picture in two directions at once. It appears as a first symptom and as a blast-crisis sign. It can also mean infection. For anyone in treatment, a fever alongside a known low neutrophil count is urgent on its own. See neutropenic fever during cancer treatment for what that pathway looks like.

Most people with CML do not need a bone marrow examination. The PDQ is direct about this. In routine presentations, it calls the value of aspiration and biopsy for every newly diagnosed patient questionable outside a clinical trial.

Marrow testing earns its place when symptoms suggest progression. In one section, the summary lists fever, malaise, rapidly enlarging splenomegaly, and more than 10% circulating blasts as reasons. In another section, the trigger is fever, enlarged spleen, or more than 20% blasts in the peripheral blood. That gap is worth asking about rather than glossing over. 10% and 20% are the accelerated and blastic thresholds. When marrow is sampled, it is checked for cellularity, fibrosis, and cytogenetics.

The molecular test does not require marrow. Reverse transcription-polymerase chain reaction, or RT-PCR, is the most sensitive method available. It can find BCR::ABL1 in peripheral blood. FISH testing can also be run on blood or marrow. For what those results mean, see what BCR-ABL means.

The Philadelphia chromosome is present in the leukemic cells of more than 95% of people with CML. It is a swap between the long arms of chromosomes 9 and 22. That swap moves the ABL1 oncogene next to the breakpoint cluster region of the BCR gene. The resulting BCR::ABL1 fusion gene makes an abnormal tyrosine kinase protein. That protein drives the disordered blood-cell production behind the symptoms.

Oral tyrosine kinase inhibitors block that protein. Imatinib mesylate has been studied most extensively. Newer TKIs with greater potency and selectivity for BCR::ABL1 have also been evaluated. With these drugs, the PDQ states that median survival is projected to approach normal life expectancy for most patients. The summary flags one practical caution. Bariatric surgery may interfere with absorption of oral TKIs, producing a weaker response.

For the wider picture, see chronic myeloid leukemia.

• NCI PDQ — Chronic Myeloid Leukemia Treatment, health professional version
• SEER Stat Facts: chronic myeloid leukemia (2026 counts projected by the American Cancer Society)