What Is Chronic Lymphocytic Leukemia?

“Chronic lymphocytic leukemia is the most common type of leukemia in the United States,” says Sangmin Lee, MD, hematologist-oncologist at Weill Cornell Medicine and NewYork-Presbyterian. Like other types of leukemia, chronic lymphocytic leukemia (CLL) begins in the stem cells of the bone marrow.

Let’s put this into context: The types of leukemia depend on which early blood cells are affected (the myeloids or the lymphocytes) and how quickly the cancer is progressing (acute or chronic). The four main types of leukemia include:

• Acute lymphocytic leukemia

• Chronic lymphocytic leukemia

• Acute myeloid leukemia

• Chronic myeloid leukemia

The lymphocytes are a type of white blood cell, and as the name suggests, they also affect the lymph nodes. “Your lymphoid [stem cells] originate from your bone marrow, and then mature and migrate into the lymph nodes,” says Dr. Lee. That’s why a common symptom of CLL is enlarged lymph nodes.

Compared to an acute type of leukemia, CLL progresses more slowly, is less likely to cause symptoms, and is less likely to require immediate and aggressive treatment. Learn more about the differences between acute and chronic leukemia.

Lymphocytes are part of the immune system. Like all blood cells, they’re made in the bone marrow, and once mature, they enter the bloodstream, where they help make antibodies, fight pathogens, and help control the immune response, according to the National Cancer Institute.

There are two types of lymphocytes: B cell lymphocytes and T cell lymphocytes. In most cases, CLL specifically affects the B cell lymphocytes (which help produce antibodies to defend against illness).

However, in an individual with CLL, the leukemia cells multiply faster than normal and healthy lymphocytes. Leukemia cells cannot fully mature, and they cannot perform the same functions as healthy lymphocytes. As a result, the leukemia cells begin to crowd out the healthy cells and inhibit the role of B lymphocytes in the body.

Once leukemia cells enter the bloodstream, they commonly spread to other organs, such as the lymph nodes and the spleen. The lymph nodes are small, bean-shaped organs throughout the body that contain lymphocytes to fight infections and illnesses. Lymph nodes are located in clusters in the neck, underarm, chest, abdomen, and groin, according to the National Cancer Institute.

“Sometimes, the only presenting symptom can be an elevated white blood cell [count] in your blood report,” says Dr. Lee. In fact, most of those are leukemia cells that are ineffective against diseases. This can make individuals with CLL vulnerable to infections.

According to Dr. Lee, other symptoms may include:

• Enlarged lymph nodes

• Fever

• Chills

• Unintended weight loss

• Enlarged spleen

• A sense of fullness

CLL vs. small lymphocytic lymphoma

Leukemia and lymphoma are different types of blood cancer, but there are so many similarities between chronic lymphocytic leukemia and small lymphocytic lymphoma (SLL) that they are often considered the same disease.

Both CLL and SLL affect the B cell lymphocytes, so once they progress, they often present the same problems and are treated similarly. There’s one key difference: When the bulk of the cancer cells are in the bloodstream and bone marrow, doctors diagnose it as CLL; when they’re mostly in the lymph nodes — and hardly in the bloodstream — it’s diagnosed as SLL, according to the Lymphoma Research Foundation.

“Knowing exactly what kind of leukemia you have is extremely important for treatment purposes and for prognosis,” says Dr. Lee.