What Is CLL?

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What Is Chronic Lymphocytic Leukemia (CLL)?

CLL is a type of cancer of the blood and bone marrow. CLL cells are found primarily in the bloodstream, the bone marrow, the lymph nodes, and the spleen. It typically progresses slowly, usually affecting older adults. Treatment for CLL isn’t always needed right after diagnosis.1,2

Small lymphocytic lymphoma (SLL) is a similar disease to CLL, but with one key difference: SLL cancer cells are found mostly in the lymph nodes instead of in the blood and bone marrow.3

What Causes CLL?

To understand CLL better, it may be helpful to review some basics about blood and how CLL can interfere with the important function of your blood cells.4-10

Parts of Blood

Blood is made up of plasma and blood cells. Plasma is the liquid part of the blood in which the solid parts—white blood cells, red blood cells, and platelets—are suspended.

B Cells

B cells are a type of white blood cell that produces antibodies that attack harmful invading cells such as the common cold virus and the flu.

B Cells and CLL

CLL begins when a single B cell becomes cancerous. This cancerous cell then copies itself, creating more cells that don’t fight infection as well as normal disease-fighting white blood cells.

B-Cell Takeover

In people with CLL, cancerous B cells take up room in the bone marrow that’s needed for healthy cells. That means there won’t be enough red blood cells and platelets, which can lead to getting sick easily, feeling tired, and losing weight.

What Are the Signs and Symptoms of CLL?

Some people with CLL don’t have symptoms. When they do occur, symptoms often develop gradually, with those who are affected seeing little to no changes in their health for years.

Some signs and symptoms of CLL include4:

Getting tired more easily

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Shortness of breath

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Swollen lymph nodes or spleen

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Repeated infections

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Unexplained weight loss

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People with CLL may also experience aches, fever, and night sweats.

CLL Quick Facts

If you have CLL, you are not alone.11


new cases

Estimated number of new cases of CLL in the United States in 2020

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65 to 74 years

Age range in which CLL is most often diagnosed

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of leukemia cases

CLL is the most common type of leukemia in adults over 19 years of age

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What Are the Risk Factors for CLL?

There are a few known risk factors for CLL, including11-13:


CLL is almost twice as common in men as in women.


About 90% of people diagnosed with CLL are over 50 years old, and the median age of diagnosis is 70.

Family history

Most people living with CLL do not have a family history of CLL, although 5% have a relative who has had some kind of leukemia.


In the US, CLL is more common among Caucasians as compared to African American and Asian populations. The risk of CLL is also higher for people of Ashkenazi Jewish descent.

Exposure to certain hazards

Exposure to large amounts of radiation and certain chemicals (Agent Orange, for example) has been linked to CLL.

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How Is CLL Diagnosed?

Your primary doctor may recognize the signs and symptoms of CLL but may refer you to a specialist doctor called a hematologist-oncologist for diagnosis. This type of doctor specializes in the diagnosis and treatment of blood cancers.9

An orange circle containing a large blood droplet and a magnifying glass showing blood cells

CLL is often discovered from the results of a routine blood test and suspected when the white blood cell count is high. Additional blood tests are needed to confirm a diagnosis of CLL. For some people, a biopsy of lymph nodes is done if the blood tests are inconclusive.9

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Blood and tissue samples are examined in laboratories using tests such as flow cytometry that can count your B cells to see if the number is too high.9

Navigating Your CLL Diagnosis

It’s important to ask your doctor about the types of tests you’ll need and how often you’ll need to have them. This may include genetic testing, which can provide critical information about your specific CLL type and help your doctor create a personalized treatment plan for you.9

The results of diagnostic testing can help your doctor “stage” your CLL or SLL. Staging is a rating that provides your doctor with a way to understand the expected outcome of your cancer. It may also help your doctor decide when it’s time to start discussing treatment.9,14

Rai Staging System for CLL

The Rai (pronounced “rye”) staging system is commonly used for CLL. It includes 5 stages, with the chance of cancer getting worse as the number increases from Stage 0 to Stage 4.


High white blood cell count but a low likelihood of cancer getting worse


Stage 0 and enlarged lymph nodes with a medium chance of the cancer getting worse


Stage 0-1 and an enlarged spleen, liver, or sometimes both, with a medium chance of the cancer getting worse


Stage 0-2 and low hemoglobin level (a protein in red blood cells) or low hematocrit (a measurement of red blood cell volume) with a high probability of the cancer getting worse


Stage 0-3 and low platelet count with a high probability of the cancer getting worse

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SLL staging follows the Lugano classification system. In this system, there are 4 stages that are based on where SLL cells are found in the body.


SLL cells are found in 1 group of lymph nodes

There is also a Stage 1E, in which SLL cells are found in an organ outside of the lymph system


SLL cells are found in 2 or more groups of lymph nodes—all above, or all below the diaphragm (the thin band of muscle that separates the chest and abdomen)

There is also a Stage 2E, in which SLL cells are found in 1 or 2 groups of lymph nodes and  in 1 nearby organ

Sometimes, in Stage 2 or later, SLL can be considered “bulky disease.” This term is often used to describe large tumors in the chest


SLL cells are found in groups of lymph nodes both above and below the diaphragm or in lymph nodes above the diaphragm and in the spleen


SLL cells have spread widely and are found in at least 1 organ outside the lymph system, such as the bone marrow, liver, or lung

Learning From Genetic Markers for CLL

We have many genetic markers on each of our 46 chromosomes. A genetic marker is a specific sequence of DNA that is identifiable at a known spot on a chromosome.16

Through genetic lab tests, your doctor can further understand the type of CLL you have. Several types exist, such as17,18

Deletion 17p

Deletion 13q 

Deletion 11q

Trisomy 12

Mutated or
Unmutated IgHV

Once your doctor knows your type of CLL, potential treatment options may become clearer. Certain treatments have been shown to work better than others based on the type of CLL. Talk to your doctor to understand how genetic testing fits into your unique CLL care plan.9,18

Staying Connected to Your Care

If coping with CLL seems like a lot to bear, remember that you are not alone.

can go a long way in helping you feel supported and confident in the steps you take to manage your CLL.9

Set your CLL therapy goals with your healthcare team

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