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What Is Chronic Lymphocytic Leukemia (CLL)?

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By Editorial Team

3 min read

Reviewed by: HU Medical Review Board | Last reviewed: December 2023

Chronic lymphocytic leukemia (CLL) is a type of cancer that affects the blood and bone marrow. It is characterized by the gradual increase of abnormal white blood cells called lymphocytes. These abnormal cells can crowd out normal blood cells, potentially leading to problems such as impacting the immune system's ability to fight infections.1-3

Most forms of CLL grow slowly, with the cancerous cells increasing over a long time. Many people do not have symptoms initially, but the cancerous cells can eventually spread to areas such as the lymph nodes, liver, or spleen. However, CLL can be more difficult to treat than acute leukemias.1

How common is CLL?

Compared to certain other types of cancer, CLL is relatively rare. But it is one of the most common types of leukemia in adults. Thousands of people are diagnosed with CLL each year. The incidence increases with age, and it is more common in men than in women. CLL rarely occurs in children.1-3

How does chronic lymphocytic leukemia develop?

The cells that make up the blood (such as red blood cells, white blood cells, and platelets) are made in the bone marrow, the spongy center inside your bones. Each type of blood cell has its own purpose:4,5

  • Red blood cells carry oxygen to tissues.
  • White blood cells are important for the immune system and help fight infections.
  • Platelets help stop bleeding by creating clots.

All blood cells begin as blood stem cells, which are immature cells that can become different types of cells in the body. These cells convert into myeloid cells or lymphoid cells. Lymphoid cells can become cells such as B cells, T cells, and natural killer cells.4,5

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CLL is a blood cancer that begins in lymphoid cells. The majority of CLL cases start in B cells. CLL that starts in T cells is much less common. Examples of rare forms of CLL include:1,2,6

  • Prolymphocytic leukemia (PLL)
  • Large granular lymphocyte (LGL) leukemia
  • Hairy cell leukemia

There are 2 main types of CLL:1-3,6

  • Slow-growing CLL – Here, the disease progresses slowly and patients may not experience symptoms for a long time.
  • Fast-growing CLL – Here, the disease advances more quickly and is more serious.

What are the risk factors?

The exact cause of CLL is not well understood, but certain risk factors may increase the likelihood of developing the disease. Risk factors may include:1,2

  • Having a family history of CLL
  • Increasing age
  • Exposure to certain chemicals, like pesticides and Agent Orange (a chemical used during the Vietnam War)
  • Being male

What are the symptoms of CLL?

CLL may be diagnosed before a person notices any symptoms. Often, routine blood work uncovers a CLL diagnosis. Symptoms that do occur may be vague or easily mistaken as resulting from another illness. Common CLL symptoms include:1-3,6

How is chronic lymphocytic leukemia staged?

Staging describes how much the cancer has spread and where it is in the body. CLL is often described as stage 0, 1, 2, 3, or 4. These range from lowest risk (stage 0) to highest risk (stage 4). Doctors use this information to decide how best to treat the cancer.1,3

How is CLL treated?

The approach to treating CLL depends on various factors, including the stage of the disease, the person’s overall health, and the presence of certain gene changes (genetic mutations). Common treatment options include:3,6

  • Watchful waiting – In the early stages or for people without symptoms, regular monitoring without immediate treatment may be appropriate.
  • Chemotherapy – Traditional chemotherapy drugs may be used to kill cancer cells.
  • Radiation therapy – Radiation may be used to kill cancer cells.
  • Targeted therapy – Medicines that target certain features of cancer cells, such as tyrosine kinase inhibitors, may be used.
  • Immunotherapy – Treatment that helps the body's own immune system attack cancer cells.

What is the prognosis for CLL?

The projected outcome of CLL for each person is based on many factors, including:6,7

  • Stage of the disease
  • Age
  • Overall health

Over the past few decades, the survival rate for all types of leukemia, including CLL, has steadily increased. Survival rates are based on the outcomes of people who have survived a certain amount of time after their diagnosis. In cancer estimates, experts typically use the 5-year survival rate as a marker.7

According to the National Cancer Institute (NCI), the 5-year survival rate for CLL is 88 percent. It is important to remember that many people live well past 5 years after diagnosis. Every case is different.7

Work with your healthcare team

CLL is serious, but there are treatment options. Work closely with your healthcare team to understand what stage your cancer is in, discuss treatment options, and actively participate in decisions regarding your care.