Chronic Lymphocytic Leukemia Facts

April 19, 2024 
This page was reviewed under our medical and editorial policy by Guido Marcucci, M.D., Chair, Department of Hematologic Malignancies Translational Science, City of Hope Duarte

Chronic lymphocytic leukemia, also known as CLL, is a type of blood cancer. CLL accounts for an estimated 33% of all new leukemia cases in the United States.

About 22,720 new cases of CLL are estimated to be diagnosed in 2026.

This guide to chronic lymphocytic leukemia causes, risk factors and statistics is designed to help patients and their families learn more about CLL.

What Is Chronic Lymphocytic Leukemia?

CLL is a type of chronic leukemia that begins in the lymphocytes, a type of white blood cell found in the bone marrow — the spongy tissue in bones — which is part of the immune system. With CLL, the lymphocytes become abnormal, which makes it harder for the body to fight infections. The abnormal cells leave less room for healthy blood cells.

This type of cancer is considered chronic because it grows and worsens slowly, in contrast to acute leukemias, which get worse more quickly without treatment.

While this cancer type mainly impacts the blood and bone marrow cells, it may spread to other areas of the body.

What Causes Chronic Lymphocytic Leukemia?

While the exact cause of leukemia is not fully understood, researchers do know that chronic lymphocytic leukemia is the result of genetic mutations. These may be inherited or result from environmental exposures.

When chromosome changes lead to genetic changes that impact cell growth and the ability to suppress tumors, CLL may occur.

CLL Risk Factors

Certain factors may increase a patient’s risk for developing CLL. Some are inherited and out of a person’s control, while others are linked to lifestyle or environmental exposures. It’s important to remember, however, that having one or more risk factors doesn’t mean a person will go on to develop CLL.

The risk factors listed below have been linked to CLL.

Chemicals and radiation: Exposure to the radioactive gas radon is associated with an increased risk. Some research also points to links between CLL and farming pesticides as well as Agent Orange, a chemical defoliant used during the Vietnam War.

Family history: Patients who have a first-degree relative with CLL have more than double the risk compared to someone without a family history of this cancer.

Age and gender: Men have a slightly higher risk for developing CLL. Risk also increases with age.

Ethnicity: CLL is more commonly seen within Europe and North America and is less commonly seen in Asia.

Is CLL Hereditary?

While a family history of the disease is considered a risk factor for CLL, chronic lymphocytic leukemia is not necessarily a hereditary type of cancer. Inherited DNA mutations rarely cause CLL, as this disease is more closely linked to genetic changes that occur during a person’s life.