What is chronic lymphocytic leukemia (CLL)?

Chronic lymphocytic leukemia (CLL) is a cancer of lymphocytes. Lymphocytes are white blood cells that help fight infection. CLL starts in a kind of lymphocyte called a B cell. The cancer cells build up in the blood, bone marrow, lymph nodes, and spleen. Bone marrow is the soft, spongy tissue inside your bones where blood cells are made. "Chronic" means it usually grows slowly. The CLL cells look grown-up, but they do not work the way healthy B cells do. Over time, they can crowd out healthy blood cells. This can lead to anemia (low red blood cells), low platelets, and a weaker immune system.

When should I call my care team?

Fever of 100.4 F (38 C) or higher, or shaking chills; Cough with fever, trouble breathing, or chest pain; A painful rash with blisters on one side of the body (possible shingles); Bleeding that will not stop, black or bloody stools, blood in your urine, or a severe headache (especially if you take a BTK inhibitor); A racing, pounding, or irregular heartbeat, fainting, or chest pain; Passing much less urine than usual, muscle cramps, or a fast heartbeat in the first weeks of venetoclax (possible tumor lysis syndrome); Yellow skin or eyes, dark urine, or sudden severe tiredness (possible breakdown of red blood cells); Many new bruises or tiny red or purple spots on the skin; A lymph node that grows quickly, new high fevers, or drenching night sweats and weight loss; Vomiting or diarrhea that will not stop, or you cannot keep down your pills or fluids.

Chronic lymphocytic leukemia (CLL)

CLL is a slow-growing blood cancer. Many people do not need treatment for years, and today's pills and fixed-length treatments help most people live well for a long time.

Hi, I'm Rosa. Today we'll go through chronic lymphocytic leukemia, or CLL, together, one step at a time. I'll keep it simple, and you can pause me, go back, or skip ahead whenever you like. Just so you know, this is for learning only. It is not medical advice, so please check everything with your own doctor and care team. Okay, let's get started.

What CLL is

Let's start with the basics. CLL stands for chronic lymphocytic leukemia. It is a cancer of white blood cells called B cells. These cells normally help fight infection. In CLL, too many of them build up in the blood, bone marrow, and lymph nodes. Chronic means it usually grows slowly. Many people feel fine. CLL is often found by chance on a routine blood test. It is the most common leukemia in adults. It usually cannot be cured, but it is very treatable. Many people live well with it for many years.

Types and related conditions

Let's talk briefly about the types. When the cells are mostly in the blood, it is called CLL. When they are mostly in the lymph nodes, it is called small lymphocytic lymphoma, or SLL. It is the same disease and is treated the same way. Some people have just a few CLL-like cells in the blood. That is not cancer. It is only checked with blood tests. Rarely, CLL can change into a faster-growing lymphoma. Your care team will tell you which one you have.

Tests you may have

Now let's talk about tests. Good news, CLL can usually be found with blood tests alone. A blood count measures your white cells, red cells, and platelets. A special test looks at markers on the cells to confirm it is CLL. Gene tests on the blood help your team pick the best treatment. Your doctor will also feel your neck, armpits, and belly for swollen glands. A bone marrow test or scans are only needed for some people. Before some treatments, you will be tested for hepatitis B.

Stages and when to treat

Next up, the stage. CLL is staged with a blood count and a physical exam. Doctors check for swollen glands, a big spleen, and low red cells or platelets. Here is the important part. Many people with CLL do not need treatment right away. Doctors call this watch and wait. You have regular checkups and blood tests. Studies show starting early does not help people live longer. Treatment starts when CLL causes problems. That could be low blood counts, big glands, or fevers and night sweats.

Gene tests and risk

Before we move to treatment, there are some things to know. Gene tests on your CLL cells help predict how fast it may grow. They also help pick the treatment that will work best. One key test looks for a change in chromosome 17, or in a gene called TP53. If you have it, chemotherapy works poorly, and targeted pills work much better. Another test looks at a gene called IGHV. Some tests are repeated before each new treatment. Your doctor will tell you what your results mean. The Questions to ask page can help you prepare.

Main treatments

Now let's talk about treatment. Most people today get targeted medicines, not chemotherapy. There are two main ways. One is a daily pill that blocks a protein called BTK. You keep taking it as long as it works. The other is a set course, often about one year, and then you stop. A common one is the pill venetoclax with an antibody given by IV. Both ways work very well. Your team will help you choose. If CLL comes back, there are more good options. Clinical trials may offer new ones too.

Infections and side effects

Let's look at side effects. CLL weakens the immune system, even without treatment. So infections are the biggest worry. Vaccines and hand washing really matter. Do not get live vaccines. Call right away for a fever. The daily BTK pills can cause easy bruising, high blood pressure, or an uneven heartbeat. Tell every doctor and dentist you take one. Venetoclax starts at a low dose to protect your kidneys. You will drink lots of water and have blood tests. Some foods, like grapefruit, can affect your pills. We have a whole side effects guide on this site.

Living well with CLL

Now let's talk about living well. For most people, CLL is a long-term condition. Many people work, travel, and enjoy family life. Watch and wait can feel worrying. That is normal. Remember, your blood tests will catch changes. Keep up with your vaccines, and ask your family to get theirs too. Protect your skin from the sun, and get a skin check each year. Call your care team for a fever or trouble breathing. If it feels very bad, call 911. Also visit our Screening, prevention and survivorship section.

You did great today. Thank you for learning with me. Write down your questions and bring them to your next visit. You can call your care team any time, day or night. CLL is often a long road, and many people walk it well for years. You are not alone.

Call your care team right away if you have

Fever of 100.4 F (38 C) or higher, or shaking chills
Cough with fever, trouble breathing, or chest pain
A painful rash with blisters on one side of the body (possible shingles)
Bleeding that will not stop, black or bloody stools, blood in your urine, or a severe headache (especially if you take a BTK inhibitor)
A racing, pounding, or irregular heartbeat, fainting, or chest pain
Passing much less urine than usual, muscle cramps, or a fast heartbeat in the first weeks of venetoclax (possible tumor lysis syndrome)
Yellow skin or eyes, dark urine, or sudden severe tiredness (possible breakdown of red blood cells)
Many new bruises or tiny red or purple spots on the skin
A lymph node that grows quickly, new high fevers, or drenching night sweats and weight loss
Vomiting or diarrhea that will not stop, or you cannot keep down your pills or fluids

Side effects: what helps

Sources

Quick answers

What is chronic lymphocytic leukemia (CLL)?: Chronic lymphocytic leukemia (CLL) is a cancer of lymphocytes. Lymphocytes are white blood cells that help fight infection. CLL starts in a kind of lymphocyte called a B cell. The cancer cells build up in the blood, bone marrow, lymph nodes, and spleen. Bone marrow is the soft, spongy tissue inside your bones where blood cells are made. "Chronic" means it usually grows slowly. The CLL cells look grown-up, but they do not work the way healthy B cells do. Over time, they can crowd out healthy blood cells. This can lead to anemia (low red blood cells), low platelets, and a weaker immune system.
When should I call my care team?: Fever of 100.4 F (38 C) or higher, or shaking chills; Cough with fever, trouble breathing, or chest pain; A painful rash with blisters on one side of the body (possible shingles); Bleeding that will not stop, black or bloody stools, blood in your urine, or a severe headache (especially if you take a BTK inhibitor); A racing, pounding, or irregular heartbeat, fainting, or chest pain; Passing much less urine than usual, muscle cramps, or a fast heartbeat in the first weeks of venetoclax (possible tumor lysis syndrome); Yellow skin or eyes, dark urine, or sudden severe tiredness (possible breakdown of red blood cells); Many new bruises or tiny red or purple spots on the skin; A lymph node that grows quickly, new high fevers, or drenching night sweats and weight loss; Vomiting or diarrhea that will not stop, or you cannot keep down your pills or fluids.

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.