CLL vs CML
How to tell CLL and CML apart when a board question makes them look alike.
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BCR-ABL positivity on molecular testing is the defining discriminator for CML.
Side by side
Older patient with persistent absolute monoclonal B-cell lymphocytosis and smudge cells suggests chronic lymphocytic leukemia.
Marked leukocytosis with left-shifted myeloid precursors, basophilia, and BCR-ABL positivity suggests chronic myelogenous leukemia.
CLL is a clonal mature B-cell neoplasm with accumulation of apoptosis-resistant lymphocytes.
CML is a myeloproliferative neoplasm driven by constitutive BCR-ABL tyrosine kinase activity.
CLL diagnosis requires clonal B-lymphocytes >=5000/uL for at least 3 months with flow cytometry showing CD5+, CD19+, CD23+ phenotype and often smudge cells.
CML shows high WBC often >25,000/uL with myelocyte bulge, absolute basophilia, low leukocyte alkaline phosphatase score, and Philadelphia chromosome t(9;22) with BCR-ABL PCR positivity.
The trap
A very high white count can be misread as CML in both diseases. The resolving clue is lineage and genetics: clonal CD5+ B-cell lymphocytosis supports CLL, while myeloid left shift with basophilia and BCR-ABL confirms CML.
The repair move
Next best step: confirm lineage and driver mutation before treatment decisions. Send peripheral blood flow cytometry when lymphoid disease is suspected, and send BCR-ABL PCR or FISH when myeloid left shift or basophilia is present. Start targeted therapy such as imatinib 400 mg orally daily for confirmed chronic-phase CML, while asymptomatic early CLL is commonly observed with close follow-up.
Try a free question
CoreA 64-year-old man has WBC 98,000/uL, splenomegaly, basophilia, and left-shifted myeloid cells on smear. What is the next best step in management?
Show answer and explanation
Answer: A. Order BCR-ABL molecular testing. When CML is suspected, confirming BCR-ABL is the key immediate step that directs targeted therapy.
Why the other choices are tempting
- B. Rituximab targets B-cell disease and is not first-line empiric therapy for suspected CML.
- C. No infection syndrome is described, and antibiotics do not address myeloproliferative disease.
- D. Leukocytosis alone cannot distinguish CML from other leukemias.
- E. Splenectomy is not first-line initial management for suspected CML.
Flashcards
Tap a card to flip it.
Which molecular finding immediately identifies chronic myelogenous leukemia?
Detection of BCR-ABL from the Philadelphia chromosome identifies CML.
What flow cytometry pattern supports chronic lymphocytic leukemia?
Clonal B cells coexpressing CD5, CD19, and CD23 support CLL.
Quick answers
What is the fastest way to tell CLL from CML?
BCR-ABL positivity on molecular testing is the defining discriminator for CML.
What is the key clue for CLL?
Older patient with persistent absolute monoclonal B-cell lymphocytosis and smudge cells suggests chronic lymphocytic leukemia.
What is the key clue for CML?
Marked leukocytosis with left-shifted myeloid precursors, basophilia, and BCR-ABL positivity suggests chronic myelogenous leukemia.
What is the common trap with CLL vs CML?
A very high white count can be misread as CML in both diseases. The resolving clue is lineage and genetics: clonal CD5+ B-cell lymphocytosis supports CLL, while myeloid left shift with basophilia and BCR-ABL confirms CML.