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Types of Cancer > Leukemia > Chronic Lymphocytic Leukemia (CLL) > Overview

Chronic Lymphocytic Leukemia (CLL)

Carolyn Vachani, RN, MSN, AOCN
Affiliation: Abramson Cancer Center of the University of Pennsylvania
Last Modified: August 22, 2007

This article is a more specific discussion of CLL. Please be sure to read Leukemia: The Basics first, so you have a basic understanding of leukemia.

What is CLL?

CLL is a chronic blood cancer that affects the lymphocytes, of which there are two types, B and T lymphocytes. These white blood cells are an important component of the immune system, helping to fight infection. More than 90% of CLL cases affect the B cells. In acute leukemia, one cell begins rapidly reproducing, leaving little room for healthy cells, causing symptoms to quickly develop. In CLL, the abnormal B cells accumulate over time, but the rate they are reproducing is not abnormal. Rather than overgrowth, CLL is caused by a loss of apoptosis, or programmed cell death. The B cells should die once they reach a certain number, but cancerous B cells have lost the ability to self destruct in this situation.

CLL accounts for a little over 30% of all adult leukemia cases in the United States, with an estimated 15,340 new cases diagnosed in 2007. The Leukemia & Lymphoma Society estimates that over 95,000 people are living with CLL. The average age at diagnosis is 55-60 and it is more common as age increases, but can develop as early as age 18. It is more common in men and much less common in Asian populations, compared with U.S. or European populations.

What causes CLL?

No one really knows what causes CLL. Exposure to radiation and a chemical called benzene can lead to other types of leukemia, but this is not a cause of CLL. The Veteran's Administration has concluded that exposure to Agent Orange is associated with CLL. In rare cases, more than one person in a family may have CLL, but in the large majority of cases it is not familial in nature.